Mild ovarian stimulation for IVF
1 Department of Reproductive Medicine and Gynaecology, University Medical Centre Utrecht, Heidelberglaan 100 3584 CS, Utrecht, The Netherlands 2 Academic Department of Obstetrics and Gynaecology, St George's Hospital Medical School, Cranmer Terrace, Tooting, London SW17 0RE, UK 3 Department of Obstetrics and Gynaecology and Reproductive Medicine, Hôpital Antoine Béclère, 157, rue de la Porte de Trivaux, 92141 Clamart, France 4 Centre for Reproductive Medicine, Dutch-Speaking Brussels Free University, Laarbeeklaan 101, 1090 Brussels, Belgium
5 Correspondence addressed. E-mail: m.f.g.verberg{at}umcutrecht.nl
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Abstract |
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 TOP Abstract IntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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BACKGROUND: Mild ovarian stimulation for in vitro fertilization (IVF) aims to achieve cost-effective, patient-friendly regimens which optimize the balance between outcomes and risks of treatment.
METHODS: Pubmed and Medline were searched up to end of January 2008 for papers on ovarian stimulation protocols for IVF. Additionally, references to related studies were selected wherever possible.
RESULTS: Studies show that mild interference with the decrease in follicle-stimulating hormone levels in the mid-follicular phase was sufficient to override the selection of a single dominant follicle. Gonadotrophin-releasing hormone antagonists compared with agonists reduce length and dosage of gonadotrophin treatment without a significant reduction in the probability of live birth (OR 0.86, 95% CI 0.72–1.02). Mild ovarian stimulation may be achieved with limited gonadotrophins or with alternatives such as anti-estrogens or aromatase inhibitors. Another option is luteinizing hormone or human chorionic gonadotrophin administration during the late follicular phase. Studies regarding these approaches are discussed individually; small sample size of single studies along with heterogeneity in patient inclusion criteria as well as outcomes analysed does not allow a meta-analysis to be performed. Additionally, the implications of mild ovarian stimulation for embryo quality, endometrial receptivity, cost and the psychological impact of IVF treatment are discussed.
CONCLUSIONS: Evidence in favour of mild ovarian stimulation for IVF is accumulating in recent literature. However, further, sufficiently powered prospective studies applying novel mild treatment regimens are required and structured reporting of the incidence and severity of complications, the number of treatment days, medication used, cost, patient discomfort and number of patient drop-outs in studies on IVF is encouraged.
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Introduction |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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Ovarian stimulation has become a key component of assisted reproductive technologies (ART). For 25 years, ovarian stimulation has been applied with the aim of increasing the number of oocytes in order to compensate for inefficiencies of the in vitro fertilization (IVF) procedure enabling the selection of one or more embryos for transfer (Fauser et al., 2005
). At the present time, a long gonadotrophin-releasing hormone (GnRH) agonist pituitary suppression regimen combined with relatively high doses of exogenous follicle-stimulating hormone (FSH) remains the most frequently used stimulation protocol (FIVNAT, 1997; Macklon et al., 2006). Gonadotrophin starting doses usually vary between 150 and 450 IU/day, although several randomized trials have failed to demonstrate improvements in outcome when higher doses are employed (van Hooff et al., 1993; Hoomans et al., 1999, 2002; Out et al., 2000, 2001; Latin-American Puregon IVF Study Group, 2001; Wikland et al., 2001; Yong et al., 2003).
Currently used medication regimens for ovarian stimulation are complex, expensive, may require weeks of daily injections and intense ovarian response monitoring is usually needed. Such regimens are associated with the risk of complications such as ovarian hyperstimulation syndrome (OHSS) (Fauser et al., 1999; Delvigne and Rozenberg, 2002; Aboulghar and Mansour, 2003). Other negative effects associated with ovarian stimulation include emotional stress, high drop-out rates and abdominal discomfort (Fauser et al., 2005). Moreover, uncertainties remain regarding long-term health risks (such as ovarian cancer) and an increased incidence of low birthweight and birth defects in the offspring conceived following IVF treatment (Hansen et al., 2002; Olivennes, 2002; Wang et al., 2005; Kapiteijn et al., 2006).
In 1996, Edwards et al. were the first to express concern with regard to contemporary ovarian stimulation approaches for IVF and called for the use of milder stimulation protocols (Edwards et al., 1996). The aim of mild stimulation is to develop safer and more patient-friendly protocols in which the risks of treatment are minimized (Diedrich and Ferberbaum, 1998; Olivennes and Frydman, 1998; Fauser et al., 1999; Olivennes et al., 2002; Nargund and Frydman, 2007; Pennings and Ombelet, 2007; Ubaldi et al., 2007) (Table I).
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A potential concern regarding the application of milder stimulation protocols in routine clinical practice is that a decreased ovarian response following mild stimulation will reduce pregnancy rates. However, increased efficacy of IVF laboratory procedures and the current tendency—in some parts of the world—to limit the number of embryos transferred, has reduced the need for large quantities of oocytes. Furthermore, supportive evidence regarding a potentially negative effect of supraphysiological steroid levels on endometrial receptivity (Simon et al., 1995
; Devroey et al., 2004), corpus luteum function (Fauser and Devroey, 2003; Beckers et al., 2006), oocyte and embryo quality (Valbuena et al., 2001; Baart et al., 2007) indicate that limited ovarian stimulation and response might have a beneficial effect upon implantation potential. |
Methods |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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This literature review will discuss the rationale behind milder ovarian stimulation approaches and the evidence regarding the efficacy of these protocols. In order to make a complete overview Pubmed and Medline were searched up to the end of January 2008 using the keywords IVF, ovarian stimulation protocol, mild and minimal stimulation and (modified) natural cycle. Additional searches were made using stimulation specific medications used, e.g. clomiphene citrate (CC), luteinizing hormone (LH)/FSH and aromatase inhibitors. References were selected which reported on related work whenever possible.
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Relevant physiology of follicle development |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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Complete follicular development takes over 220 days and can be classified into three phases according to the developmental stage and the follicular gonadotrophin dependence. First, the initial recruitment of resting primordial follicles, second the development of pre-antral and early antral follicles and finally cyclic recruitment of a limited cohort of antral follicles followed by the selection of a single dominant follicle during the mid-follicular phase of the menstrual cycle (Gougeon, 1996
; Fauser and van Heusden, 1997; McGee and Hsueh, 2000) (Fig. 1).
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In the adult ovary, folliculogenesis starts when follicles leave the pool of resting follicles to enter the growth phase. The size of the follicle pool is determined during fetal life and reaches its maximum of 6–7 million by 20 weeks of gestation (Baker, 1963
). From this point in time, germ cell content will decrease due to a continuous flow of follicles leaving the primordial follicle pool (initial recruitment). Around 1000 primordial follicles start growing every month. The exact mechanism underlying the initiation of growth is not well understood and appears to be under the control of intra-ovarian autocrine and paracrine factors (Gougeon, 1996; Fortune et al., 2000). The great majority of primordial follicles that enter this development phase undergo atresia before reaching the antral follicle stage, principally through apoptosis (McGee and Hsueh, 2000).
After initial recruitment, follicles entering the growth phase enlarge, both by proliferation and differentiation of granulosa cells and an increase in the size of the oocyte. The time span of the development from primary recruitment to the early antral follicle stage in humans is unknown but is proposed to be several months. During early pre-antral follicle development, FSH receptors become detectable on granulosa cells. Although at this stage the follicle seem unaffected by the absence of gonadotrophins [as shown in women diagnosed with Kallmann syndrome, or after hypophysectomy (Schoot et al., 1992)], growth may be stimulated by the presence of FSH (McGee and Hsueh, 2000).
In contrast to the early stages of follicle development, the presence of FSH is an absolute requirement for the development of larger antral follicles. From this point onwards, FSH acts as a survival factor for antral follicles, which are being rescued from atresia by the intercycle rise in serum FSH level (Fauser and van Heusden, 1997). Although each growing follicle may initially have an equal potential to reach full maturation, only those follicles continue to grow that are at a more advanced developmental stage (2–5 mm in diameter) at the time FSH levels surpass the threshold during the luteo-follicular transition. The number of follicles available for cyclic recruitment is dependent on the age of the women and is estimated to be around 11 per ovary (Hodgen, 1982; Pache et al., 1990) (Fig. 2).
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After the initial rise, FSH concentrations plateau during the early follicular phase and finally decrease during the mid to late follicular phase as a consequence of inhibin B and ovarian steroid negative feedback (Zeleznik et al., 1985
; Groome et al., 1996; Schipper et al., 1998). The decrease in FSH limits the time that the FSH concentration is above the threshold, which appears to be essential for single dominant follicle selection (van Santbrink et al., 1995) (Fig. 2). Despite the decline in FSH, the most mature follicle continues its growth due to its increased sensitivity for FSH and acquired responsiveness to LH (Hillier, 1994; McGee and Hsueh, 2000). All other recruited follicles lack sufficient FSH stimulation and enter atresia. The ‘FSH gate’ (Baird, 1987) or ‘FSH window’ (Fauser et al., 1993) concept introduces the element of time rather than the magnitude of the FSH rise to the FSH threshold theory. The window concept emphasizes the importance of a transient increase of FSH above the threshold level in order to gain single dominant follicle selection. Ovarian stimulation makes use of the concept that disruption of the decline of FSH levels leads to the development of multiple dominant follicles (Fig. 3).
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After exogenous gonadotrophins became available, growth of multiple dominant follicles was accomplished by the administration of high doses of gonadotrophins during the entire follicular phase (Hillier et al., 1985
; Oehninger and Hodgen, 1990) (Fig. 3). However, a later study in primates showed that mild interference with the decrease in FSH levels during the mid-follicular phase is sufficient to override the selection of a single dominant follicle (Zeleznik et al., 1985). Subsequently, this concept was confirmed in humans; a moderate, but continued, elevation of FSH levels during the mid to late follicular phase (effectively preventing decremental FSH concentrations) was sufficient to interfere with single dominant follicle selection and induces ongoing growth of multiple follicles in normo-ovulatory volunteers (Fig. 4) (Schipper et al., 1998) and (Fig. 5) (Hohmann et al., 2001).
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The development of milder stimulation protocols |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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Introduction of GnRH antagonists
The introduction of GnRH antagonists into clinical practice has allowed for the introduction of milder stimulation approaches for IVF treatment (Tarlatzis et al., 2006). GnRH antagonists prevent the premature LH rise by competitive blockade of the GnRH receptor. Unlike GnRH agonists, GnRH antagonists do not induce an initial flare of endogenous gonadotrophin release, but cause an immediate and rapid, reversible suppression of gonadotrophin secretion. The use of GnRH antagonist exclusively during the mid to late stimulation phase (the period at risk for a premature rise in LH) therefore allows for the initiation of the IVF treatment cycle in a normal menstrual cycle with an undisturbed recruitment of a cohort of follicles during the early follicular phase. This approach enables the endogenous inter-cycle FSH rise to be utilized rather than suppressed, resulting in a reduction of medication needed. The use of ovarian stimulation in the normal menstrual cycle also enables more IVF cycles to be carried out in a given period than is possible with a long GnRH agonist stimulation protocol.
Three general approaches for GnRH antagonist co-treatment have emerged. A single large dose can be injected subcutaneously on approximately the eighth day of stimulation with gonadotrophins. Alternatively, daily injections of small doses could be initiated on a fixed day of stimulation (usually Day 6) or depending on the size of the dominant follicle or the estradiol level (flexible protocol) and continued until the day that human chorionic gonadotrophin (hCG) for final oocyte maturation is given (for review Huirne and Lambalk, 2001).
As was shown in a meta-analysis of 27 IVF studies, the use of GnRH antagonist co-treatment compared with agonist long protocol leads to a considerable reduction in the number of days GnRH analogue treatment is needed [weighted mean difference (WMD) –20.90, 95% CI –22.20 to –19.60], the number of days of gonadotrophin administration (WMD –1.54, 95% CI –2.42 to –0.66), the amount of gonadotrophin ampoules used (WMD –4.27, 95% CI –10.19 to 1.65) and the incidence of severe OHSS (RR 0.61, 95% CI 0.42–0.89) (Al-Inany et al., 2006).
Moreover, the use of GnRH antagonists is not complicated by cyst formation due to the GnRH agonist flare-up effect. Although initial studies suggested a detrimental effect on pregnancy rates following GnRH antagonist compared with agonists (Ludwig et al., 2001; Al-Inany et al., 2006; Tarlatzis et al., 2006), a recent meta-analysis including 22 randomized controlled trials (RCT) involving 3176 subjects showed no significant difference in the probability of live birth (OR 0.86, 95% CI 0.72–1.02) (Kolibianakis et al., 2006).
To date, GnRH agonists remain in use in the majority of clinics. This is probably due to the established position of GnRH agonist in standard regimens (Kolibianakis et al., 2005), initial reports on a possible reduction in pregnancy rates (Al-Inany et al., 2006) and the reduced flexibility in the programming of IVF cycles with GnRH antagonist co-treatment (Fauser and Devroey, 2005).
Natural cycle and modified natural cycle with FSH add-back
The first successful IVF treatment was performed in an unstimulated menstrual cycle (Steptoe and Edwards, 1978). Soon thereafter, IVF in natural cycles was largely replaced by ovarian stimulation to improve the success rate per cycle (Trounson et al., 1981; Cohen et al., 2005; Macklon et al., 2006). Natural cycle IVF in its basic form consists of simply monitoring the spontaneous cycle, and retrieving a single oocyte prior to the spontaneous LH peak. Consequently, the chance for multiple pregnancies and OHSS are minimal. Natural cycle IVF is physically less demanding, requiring no or far less hormonal medication. The per-cycle costs of natural cycle IVF have been calculated to be 20–23% of those of stimulated IVF (Aboulghar et al., 1995; Nargund et al., 2001). Ongoing pregnancy rates per started natural cycle IVF have been reported to be 7.2%, which seems unacceptably low for most patients despite being less stressful. However, this may vary according to the population studied (for review Pelinck et al., 2002).
Natural cycle IVF results are hampered by high cancellation rates due to premature LH rises, premature ovulation or reduced chances for successful oocyte retrieval (Pelinck et al., 2002). The planning of oocyte retrieval based on a LH rise requires frequent monitoring and round-the-clock oocyte retrieval and laboratory facilities. The use of hCG for the triggering of final oocyte maturation, and indomethacin to postpone follicle rupture (Nargund et al., 2001) allows for a certain degree of planning. Flushing of the follicle during oocyte retrieval (Bagtharia and Haloob, 2005) may increase the efficacy of the procedure.
Only four RCTs involving a total of 339 women comparing natural cycle IVF with stimulated IVF cycles have been published so far (Table II). The outcome of natural cycle IVF was compared with IVF in CC-stimulated cycles (MacDougall et al., 1994; Ingerslev et al., 2001), human menopausal gonadotrophin (HMG)/GnRH agonist long protocol cycles (Levy et al., 1991) or with IVF cycles combining purified FSH ovarian stimulation with a GnRH agonist microdose flare protocol (Morgia et al., 2004). Despite relatively small numbers of patients, and variable numbers of treatment cycles per patient, natural cycle IVF was consistently observed to result in lower pregnancy rates (Table II).
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To improve effectiveness, natural cycle IVF could be offered as a series of treatment cycles, for it is safer, less stressful compared with conventional stimulation. It has been postulated that after four cycles of natural cycle IVF, the cumulative probability of pregnancy is
46% with an associated live birth rate of 32% in a selected groups of patients (Nargund et al., 2001). In this study, 52 patients with a regular menstrual cycle underwent 181 natural cycle IVF attempts which resulted in 16 live births. Even though the outcome of four cycles of natural cycle IVF was found to be comparable to a single cycle of IVF with ovarian stimulation and being cost-effective, the added investment of time and increased number of oocyte retrieval procedures also should be taken into account. To improve outcomes while preserving the advantages of natural cycle IVF, modifications have been made. In the ‘modified’ natural cycle, the occurrence of a premature LH rise is prevented by the use of a GnRH antagonist during the late follicular phase. The ongoing growth of the dominant follicle is supported by the addition of exogenous gonadotrophins (referred to as ‘add back’). In most studies, GnRH antagonist and gonadotrophins (75–300 IU/day) are initiated at a follicle diameter of 12–17 mm.
Up to the present, no RCTs studying the efficacy of modified natural cycle IVF have been published. Most studies regarding modified natural cycle IVF include patients with a previous poor response to conventional ovarian stimulation. In this population, success rates between 0 and 14%per started cycle have been reported in non-randomized studies (Elizur et al., 2005; Castelo-Branco et al., 2004; Kolibianakis et al., 2004; Weghofer et al., 2004; Hur et al., 2005). One large cohort study analysed the cumulative pregnancy rate after three modified natural IVF cycles in good prognosis patients (Pelinck et al., 2006). A total of 844 treatment cycles in 350 patients of <36 years of age with no previous IVF treatment were included. The ongoing pregnancy rate per cycle was 8.3 and 20.8% after up to three cycles. The number of cancelled cycles related to a rise in LH or ovulation in this study was 13% per started cycle, compared with an average of 20% reported following natural cycle IVF.
Relatively high pregnancy rates have been reported in young couples with severe male infertility as the only fertility compromising factor. In this category of patients, the success rate per started cycle was 13.3% (Zhioua et al., 2004) and cumulative pregnancy rates of 43.8% after six successive cycles (Vogel et al., 2003) have been reported.
These studies show that (modified) natural cycle is a safe and patient friendly treatment option. Despite the advantages of this approach, low efficacy has restricted its widespread use. Modified natural cycle IVF in consecutive cycles in a selected population may result in improved effectiveness.
The anti-estrogen CC was the first preparation used for ovarian stimulation in IVF (Trounson et al., 1981; Quigley et al., 1984; Cohen et al., 2005). CC has now been largely replaced by more effective HMG/FSH protocols in combination with GnRH analogue co-treatment (Fraser and Baird, 1987; Macklon et al., 2006). Important advantages of CC compared with gonadotrophins remain including its oral administration, low price and widespread availability. CC acts to increase pituitary FSH secretion by reducing negative estrogen feedback.
An ovarian stimulation protocol combining CC with gonadotrophins could lead to a reduction in the amount of gonadotrophins required due to the combined synergistic effects. Additionally, because gonadotrophins may counterbalance the undesired anti-estrogenic effects of the CC on the endometrium (Markiewicz et al., 1988; Nelson et al., 1990) which has been held responsible for the relatively low embryo implantation rates observed this combination might lead to improved pregnancy rates compared with CC alone.
Two randomized trials have compared the outcome of CC/gonadotrophin treatment cycles with a standard long GnRH agonist ovarian stimulation protocol. In one study, significantly higher cycle cancellation rates and lower pregnancy rates per cycle were observed following a CC protocol in combination with 150 IU HMG (P = 0.002) (Dhont et al., 1995). On the other hand, stimulation with goserelin/HMG was associated with a higher number of ampoules of HMG (44.9 versus 9.9; P < 0.0001) and a longer duration of stimulation (11.2 versus 8.7 days; P < 0.0001). A more recent study involving similar patient numbers, concluded that a stimulation regimen combining CC with 225 IU FSH and 75 IU of recombinant LH (rLH) on alternate days resulted in comparable cancellation and ongoing pregnancy rates per cycle to those following a standard long GnRH agonist protocol (Weigert et al., 2002). The average number of ampoules of FSH used was significantly reduced in the CC group (13.9 versus 16.6 ampoules; P < .0001). The characteristics of the RCTs on the various CC protocols for IVF treatment have been summarized in Table III.
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The recent availability of GnRH antagonists has allowed for the prevention of premature LH rises in combination with CC. One randomized controlled study showed that a CC/gonadotrophin regimen with GnRH antagonist co-treatment resulted in similar pregnancy outcomes compared with a standard long GnRH agonist stimulation protocol while significantly reducing the number of ampoules HMG used, the number of treatment days and the number of oocytes retrieved (Lin et al., 2006
). This study confirmed the findings of two earlier retrospective analyses which concluded that equally high pregnancy rates could be obtained with a CC/gonadotrophin protocol with GnRH antagonist co-treatment compared with standard ovarian stimulation, with a significant reduction in the total dose of gonadotrophins needed (Williams et al., 2002; Fiedler and Ludwig, 2003). In contrast, a non-randomized comparative study observed significantly lower pregnancy rates following ovarian stimulation with a CC/HMG protocol with GnRH antagonist co-treatment compared with a long GnRH agonist protocol (Mansour et al., 2003). Whether the addition of GnRH antagonist to the CC/gonadotrophin protocol improves outcomes remains unclear. A randomized controlled study observed similar ongoing pregnancy rates with and without the use of GnRH antagonist (Fiedler et al., 2001). The need for pituitary suppression in combination with CC is probably dependent on the dosage of medication used as well as individual differences in ovarian response.
In most studies, gonadotrophins are combined with CC in a dose of 100 mg/day for 5 days during the early follicular phase. However, a high rate of heterogeneity exists in studies concerning the optimal use of the other components of this stimulation approach. It has been debated whether HMG or FSH with or without rLH supplementation should be used (Engel et al., 2002; Weigert et al., 2002). Additionally, there is no evidence regarding the optimal gonadotrophin regimen; most studies vary in the starting dose, day of initiation, daily injections or on alternate days or as a single bolus of long acting FSH (Corfman et al., 1993; Obruca et al., 1993; Engel et al., 2002; Tavaniotou et al., 2003; D'Amato et al., 2004; Kawachiya et al., 2006).
In conclusion, more studies are required to optimize the CC/gonadotrophin stimulation protocol. The heterogeneity in the studies thus far published does not allow to draw conclusions to be drawn regarding the possible benefits of CC in ovarian stimulation for IVF. However, given its low cost, CC may have a place in cost-effective mild ovarian stimulation treatments.
Aromatase inhibitors selectively inhibit the conversion of androgens to estrogens in granulosa cells of developing ovarian follicles, resulting in a subsequent increase in intra-ovarian androgens and absence of a rise in estrogens (Garcia-Velasco et al., 2005). Intra-ovarian androgens may have a profound effect on early follicle growth and increase the number of preantral and small antral follicles as androgens stimulate theca and granulosa cell proliferation and inhibit apoptosis (Vendola et al., 1998). Due to a reduced estrogen feedback and resulting increased endogenous gonadotrophin secretion, the need for exogenous gonadotrophins is likely to be reduced when aromatase inhibitors are administered in the early follicular phase. Aromatase inhibitors may therefore serve a similar purpose as CC. Like CC, aromatase inhibitors are orally taken and are cheap. However, compared with CC they offer the potential advantage of not causing depletion of estrogen receptors (Mitwally and Casper 2001, 2003) and are more rapidly cleared from the body because of their shorter half-life (45 h instead of a few weeks). In theory, significantly reduced intrafolliular estrogen concentrations may impact on oocyte quality which may affect IVF outcomes.
Aromatase inhibitors have been in clinical use for more than 20 years, primarily in the treatment of advanced breast cancer in post-menopausal patients (Winer et al., 2002). The use of these compounds have only recently been introduced in infertility treatment, especially for ovulation induction (Casper and Mitwally, 2006) and as a mild and safe ovarian stimulation method for IVF treatment in patients with breast cancer (Oktay et al., 2003, 2005). Recent data have raised concerns regarding possible teratogeneity of aromatase inhibitors (Biljan et al., 2005) and ovarian stimulation is currently an off-label use again marketer's advice. Even though these findings were not confirmed in a larger group of patients (Tulandi et al., 2006), animal studies have shown toxic effects on prenatal development in rats after exposure to letrozole in utero (Tiboni et al., 2008).
There are limited clinical data available concerning the use of aromatase inhibitors in IVF treatment. One preliminary uncontrolled study observed an ongoing pregnancy rate of 27% following the use of aromatase inhibitors as a cheap treatment alternative in 22 good prognosis patients with limited financial means (Grabia et al., 2006). In this study, HMG was initiated on cycle Day (CD) 7 after 5e days of letrozole (2.5 mg CD 3–7) with GnRH antagonist co-treatment.
To date, only three RCTs involving a total of 80 women have studied the use of aromatase inhibitors in IVF. However, aromatase inhibitors were administered in combination with a standard rather than mild ovarian stimulation protocol in all three studies. In two trials, aromatase inhibitors were added to a standard treatment schedule using high doses of gonadotrophins in patients with a poor response in a previous treatment cycle (Goswami et al., 2004; Kahraman et al., 2005). Both studies showed no benefit although the study groups were too small to draw meaningful conclusions. The third study randomized 20 good prognosis patients for the use of 150 IU rFSH from CD 2 with or without the addition of 2.5 mg letrozole and GnRH antagonist co-treatment from CD 6 (Verpoest et al., 2006). The use of aromatase inhibitors resulted in higher numbers of oocytes and a tendency towards higher clinical pregnancy rates per started cycle in the letrozole group. In conclusion, more sufficiently powered randomized studies are needed to assess the true benefit of aromatase inhibitors in IVF treatment.
Exogenous gonadotrophins with GnRH antagonist co-medication
Mild ovarian stimulation in which low-dose gonadotrophin (FSH/HMG) administration is delayed until the mid-follicular phase is based on the FSH window concept (Fauser et al., 1993, 1997). Exogenous FSH administration is limited to the mid to late follicular phase with the aim of preventing a decrease of FSH levels and thus inducing multi-follicular development (Fig. 4) (Schipper et al., 1998). The availability of GnRH antagonists for acute suppression of a premature LH rise enabled this concept to be introduced into IVF (Macklon and Fauser, 2000). A pilot study showed that multiple dominant follicles could even be induced when the initiation of FSH was postponed until CD 7 (de Jong et al., 2000). However, there was a tendency toward a lower percentage of women presenting with multiple dominant follicle development compared with patients started on CD 3 or 5 (Fig. 5) (Hohmann et al., 2001). A fixed daily dose of 150 IU rFSH compared with 100 IU/day was found to be more effective in consistently inducing multiple follicular growth when ovarian stimulation was initiated on CD 5 (de Jong et al., 2000).
In a prospective randomized study involving 142 patients, the efficacy of a stimulation protocol initiating ovarian stimulation (150 IU/day) on CD 5 (with GnRH antagonist co-treatment from a follicle size of 14 mm) was compared with a conventional long GnRH agonist protocol and a standard GnRH antagonist protocol with an early follicular phase start of FSH (Hohmann et al., 2003). This study concluded that the tested mild protocol resulted in pregnancy rates per started cycle comparable to those observed following conventional ovarian stimulation with GnRH agonist co-treatment despite a reduced duration of stimulation and a marked reduction in the amount of exogenous FSH needed (P < 0.001 and 0.02, respectively).
To investigate the use of this mild stimulation protocol in clinical practice, a large randomized efficacy study was performed to analyse whether a mild strategy in IVF [combining mild ovarian stimulation with single embryo transfer (SET)] would lead to a similar overall outcome while reducing patients' discomfort, multiple pregnancies and costs compared with a standard treatment involving conventional stimulation and the transfer of two embryos (Heijnen et al., 2007). The study included a total of 404 patients (almost 800 consecutive IVF cycles) and observed that due to the shorter duration of treatment per cycle, less medication was needed and there was a reduction in twin pregnancies, the mild approach resulted in an equal cumulative chance of term live birth after a year of treatment while significantly reducing the total costs and multiple birth (Fig. 6). Table IV shows the characteristics of four RCTs regarding a mild ‘late start, low-dose’ ovarian stimulation performed by our group.
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Analysis of factors that influence the decision of couples to discontinue treatment showed that the use of a mild treatment strategy resulted in a significant reduction in drop-out rates (Verberg et al., 2008a
). This finding shows that patients are willing to undergo more mild IVF treatment cycles as long as a mild treatment strategy is applied.
A stimulation protocol with late follicular phase replacement of FSH administration by LH has recently been proposed as an alternative mild stimulation approach. The replacement of FSH by LH is based on the acquired LH responsiveness of granulosa cells in dominant follicles (Hillier, 1994). In sheep, LH administration maintained elevated ovulatory rates despite FSH withdrawal (Campbell et al., 1999), while in humans the administration of rLH (300–750 IU/day) was found to be sufficient to maintain follicular growth in the late follicular phase after initial ovarian stimulation with exogenous gonadotrophins (Sullivan et al., 1999). Besides the expected reduction of gonadotrophin usage, this ovarian stimulation approach might also reduce the number of small, less mature follicles, conceivably reducing chances for OHSS (Filicori et al., 1999).
Three randomized trials comparing the late follicular phase hCG/LH protocol with the outcome of conventional stimulation protocols in patients with a favourable prognostic profile could be identified. In a large RCTs in 323 IVF patients the outcomes of a stimulation protocol with regular ovarian stimulation until CD 6, followed by a combination of 75 IU FSH and 200 IU hCG with GnRH antagonist co-treatment until oocyte retrieval were compared with a standard GnRH antagonist and a long GnRH agonist stimulation protocol (Serafini et al., 2006). The hCG protocol resulted in a significant reduction in rFSH needed. No difference in the number of (mature) oocytes obtained, ongoing pregnancy rates and incidence of OHSS. A similar design was applied in a study involving 109 patients, with the only exception that hCG was initiated when the largest follicle was 14 mm along with a fixed FSH dosage (Koichi et al., 2006). This study also observed similar pregnancy rates between the three groups, no difference in the number of oocytes or incidence of severe OHSS. However, a significant decrease in the total dose of gonadotrophins needed and small follicles at the time of final oocyte maturation was observed in the hCG group. Finally, the efficacy of a stimulation protocol with complete replacement of FSH with hCG from a follicular size of 12 mm in combination with a long GnRH agonist down-regulation protocol was studied (Filicori et al., 2005). This approach resulted in a significant reduction in FSH needed and less small follicles at final oocyte maturation in the hCG protocol without compromising the pregnancy rate, compared with a standard long GnRH agonist protocol. None of the studies reported untimely increments of follicular phase progesterone secretion or premature LH surges in the hCG/LH protocol.
These findings confirm that, in an selected group of patients, an ovarian stimulation protocol with late follicular phase hCG/LH stimulation leads to a reduced need of exogenous FSH and good pregnancy rates. However, despite the reported reduction in the number of small follicles, high estradiol levels were found and a reduced incidence of OHSS could not be established as yet. Additional studies are needed to determine the critical threshold for FSH replacement by LH stimulation, the most appropriate dosage of LH or hCG and establish the clinical benefit.
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Implications of mild ovarian stimulation |
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Embryo quality
Some observations suggest that ovarian stimulation affects embryo quality as assessed by morphology as well as the chromosomal constitution of the embryos (Munne et al., 1997; Katz-Jaffe et al., 2005; Baart et al., 2007). This phenomenon could be the result of interference with the natural selection of good-quality oocytes or the exposure of growing follicles to the potentially negative effects of ovarian stimulation. Supportive evidence comes from several human and animal studies reporting detrimental effects of ovarian stimulation on oocyte and embryo quality.
An increased incidence of morphology and chromosomal abnormalities have been observed in oocytes after exposure to high doses of gonadotrophins during in vitro maturation of mouse oocytes (Eppig et al., 1998; van Blerkom and Davis, 2001; Roberts et al., 2005). Ovarian stimulation and concurrent high estradiol levels were shown to have a negative impact on the developmental and implantation potential of human embryos (Valbuena et al., 1999; Ertzeid and Storeng, 2001; Van der Auwera and D'Hooghe, 2001) as well as the chromosomal constitution of embryos (Katz-Jaffe et al., 2005). Moreover, ovarian stimulation might disrupt mechanisms involved in maintaining accurate chromosome segregation (Munne et al., 1997; Hodges et al., 2002).
Mild stimulation approaches, aiming at a more physiological response, might therefore improve embryo quality. A randomized trial concerning the chromosomal competence of human embryos as assessed by preimplatation aneuploidy screening by fluorescent in situ hybridization showed a significantly higher proportion of euploid embryos following mild ovarian stimulation compared with conventional stimulation, suggesting that through maximal stimulation the surplus of obtained oocytes and embryos are of lower quality (Fig. 7) (Baart et al., 2007).
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A recent meta-analysis combining the results of three separate RCTs performed by our group suggests that the retrieval of a modest number of oocytes following mild stimulation is associated with a distinctly higher implantation rate compared with patients where the same number of oocytes is retrieved following conventional stimulation (Verberg et al., 2008b
). These observations have led to the contention that when few oocytes are obtained following mild ovarian stimulation, they are likely to represent a more homogenous group of good-quality oocytes instead of a pathological reduction in the ovarian response. These findings imply that the fear of obtaining low numbers of oocytes following mild ovarian stimulation is unjustified contradicting the assumption that an increased quantity of oocytes leads to better outcomes (Devreker et al., 1999). In fact, in most of the studies investigating the relationship between oocyte numbers and pregnancy rates, the positive effect on pregnancy rates with a growing number of oocytes eventually levels off (Devreker et al., 1999; Melie et al., 2003; Kok et al., 2006) or falls (Van der Gaast et al., 2006).
A potential disadvantage of the development of lower numbers of oocytes might be the reduction of supernumerary embryos for cryopreservation to transfer in subsequent (unstimulated) cycles. However, as was discussed previously, the number of good-quality embryos resulting from mild ovarian stimulation was found to be similar to that following a conventional stimulation protocol and should therefore lead to a equal total number of pregnancies (Baart et al., 2007). Furthermore, in view of the many legal and ethical issues relating to cryopreserved embryos, the possibility of cryopreserved supernumerary oocytes rather than embryos has recently been proposed (Jain and Paulson, 2006).
Luteal function and endometrial receptivity
Ovarian stimulation affects luteal phase function and alters endometrial receptivity. This negative effect of ovarian stimulation has largely been held responsible for the impaired embryo implantation compared with natural cycles utilized in oocyte donation (Paulson et al., 1990). The exact pathophysiology remains unclear although supraphysiological steroid levels are widely held responsible (Beckers et al., 2003) (for review Fauser and Devroey 2003; Strowitzki et al., 2006). A negative influence of supraphysiological estradiol levels on implantation rates has been clearly established; estradiol levels >3000 pg/ml on the day of hCG administration resulted in reduced implantation rates independent of embryo quality (Simon et al., 1995). Mild stimulation approaches, aiming at a more physiological response, might therefore improve embryo implantation rates (Devroey et al., 2004). Indeed, increased pregnancy rates have been observed following a FSH step-down regimen for high response patients when estradiol levels were decreased during the preimplantation period (Simon et al., 1998).
Health economics considerations
Due to the limited use of ovarian stimulating medication and the decreased chances for complications such as OHSS, the per cycle cost of mild stimulation IVF will be substantially lower compared with conventional stimulation approaches. It has been calculated that the mean cost for the treatment of OHSS ranged from $400 to 553 per day depending on the treatment strategy applied, and over 6000 dollar when the cycle was cancelled (Wittenberger et al., 2005). However, in order to analyse the cost-effectiveness of mild stimulation, the total cost per live birth may represent the best end-point. Besides the costs for medication, medical consultations and visits, laboratory charges (general, hormone and embryology), ultrasound procedures, IVF procedures (oocyte retrieval and embryo transfer), hospital charges, nurse coordinator costs, administrative charges, fees for anaesthesia, costs for complications, travel expenses and lost wages should all be taken into account (Collins, 2002).
Up to the present, there are few studies that (properly) analyse the cost-effectiveness of various mild stimulation approaches. Studies evaluating natural versus stimulated IVF showed that natural cycle IVF was more cost-effective than stimulated cycles per live birth (Daya et al., 1995; Nargund et al., 2001). However, it is not clear what aspects were included in these cost estimates. Cost per patient after up to three cycles of modified natural cycle IVF were found to be higher compared with a single cycle of conventional stimulation (Pelinck et al., 2005). In this analysis, costs of cryopreservation and OHSS were not taken into account and data for the conventional stimulation protocol were derived from the literature. CC-stimulated cycles with GnRH antagonist co-treatment were not found to be cost-effective compared with a GnRH agonist flare protocol (Kovacs et al., 2004) or a long GnRH agonist protocol (Mansour et al., 2003). However, the first study only included medication costs and although the latter included medical and treatment costs, potential additional costs were excluded.
In a prospective randomized trial regarding the efficacy of IVF using either mild ovarian stimulation in combination with SET or a long GnRH agonist co-treatment conventional stimulation protocol along with double embryo transfer, the costs and clinical outcome after 12 months of treatment were compared (Heijnen et al., 2007). This study showed that the overall costs resulting from treatment up until 12 months after randomization were lower for the mild strategy, despite a higher average number of IVF cycles (325 versus 444 cycles) for the mild strategy (Heijnen et al., 2007). However, this reduction in costs was mainly due to a reduction in multiple pregnancies and preterm births in the mild strategy (Polinder et al., 2008).
Apart from health risks, emotional stress should be considered an important negative side effect associated with IVF treatment. The stress of infertility treatment has been ranked second to that involving the death of a family member or divorce by couples undergoing IVF treatment (Freeman et al., 1985; Baram et al., 1988). Some studies even describe an increased risk of marital stress and divorces in couples undergoing IVF treatment (Wang et al., 2007), although other studies have not confirmed this (Pinborg et al., 2003; Holter et al., 2006; Repokari et al., 2007). In contrast, findings of one study even suggested that shared stress, bereavement and disappointments can increase a couple's feeling of cohesion and result in improvement in their marriage (Repokari et al., 2007). The latter only appeared to be true for couples in whom treatment also results in a (singleton) live birth (Boden, 2007; Repokari et al., 2007).
Besides a potential direct negative effect on the chance of conceiving (Verhaak et al., 2001; Smeenk et al., 2001, 2005; Cwikel et al., 2004), treatment related stress was found to be the most important reason for patients dropping out of IVF treatment (Olivius et al., 2004). The early drop-out from treatment deprives the couple an optimal cumulative chance of achieving a pregnancy, and therefore also impacts on the overall success rates of the respective IVF programme. Average drop-out rates well above 50% have frequently been reported in the literature (Callan et al., 1988; Tan et al., 1992; Land et al., 1997; Olivius et al., 2002; Schroder et al., 2004).
Mild ovarian stimulation, aiming to provide a shorter and more patient-friendly treatment with a reduction in complications, might decrease IVF treatment-related stress. Following minimal intervention (unstimulated cycle or CC), patients reported fewer side effects and stress related to hormone treatment and cycle cancellation compared with conventional stimulation (Hojgaard et al., 2001). Furthermore, mild ovarian stimulation was found to lead to a significant reduction in drop-out rates per cycle. This observation should be considered in the context of a similar level of overall discomfort despite the increased number of treatment cycles needed to achieve a similar result as a conventional treatment group (de Klerk et al., 2006; Heijnen et al., 2007). A mild IVF treatment strategy was found to be associated with fewer symptoms of depression after overall treatment failure than a standard IVF treatment (de Klerk et al., 2007). Consequently, mild stimulation might not only reduce the psychological burden of IVF treatment but it may also have a positive impact on cumulative treatment success rates as it positively affects the chance patients are willing to continue treatment following a failed attempt and therefore compensate for the lower pregnancy rate per cycle following mild stimulation (Verberg et al., 2008a).
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Current status and future developments |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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Up to now, studies on alternative (milder) stimulation protocols have been limited by the relative small numbers of patients included, poor methodological quality (there are few randomized studies) and the use of surrogate end-points such as the number of oocytes or embryos. Furthermore, many studies on alternative stimulation strategies have involved poor prognosis patients, while it is mainly the young patients that have the highest risk of complications of ovarian stimulation. Therefore, especially young women should be included in studies evaluating the possible benefits of mild stimulation. Even so, most studies in older patients failed to show a benefit of a high-dose stimulation regimen over milder forms of ovarian stimulation. As most of these patients will fail to respond well to any type of ovarian stimulation, a mild stimulation protocol may be also preferred in such patients.
Increased awareness among patients and their physicians of the burden and complications associated with ovarian stimulation will facilitate the acceptance of milder stimulation (Edwards, 2007; Nargund and Frydman, 2007; Nargund et al., 2007; Pennings and Ombelet, 2007; Ubaldi et al., 2007). Crucial to the success of implementing mild ovarian stimulation strategies will be achieving a consensus as to how success and complications of IVF treatment are reported in the literature. By reporting the incidence and severity of complications, the number of treatment days, medication used, costs, patient discomfort and drop-outs, awareness of the price paid for currently applied stimulation protocols will increase. Furthermore, a reappraisal of the current paradigm of maximizing treatment outcomes per cycle at all costs is needed (Fauser et al., 2005). The competition for patients, desire for high fertility rates and the need for quick results driving fertility practices in some countries, are factors that could cause resistance by physicians towards the use of mild ovarian stimulation. At the end, (cumulative) mild stimulation cycles might lead to a safer and more cost-effective IVF treatment strategy.
A further prior condition for implementation of mild ovarian stimulation into standard clinical practice is the availability of (reimbursed) IVF treatment. As long as IVF is not easily accessible or patients have to pay for each cycle themselves it is likely that treatment strategies with the highest pregnancy rates (and most complications) will be preferred. On the other hand, mild IVF could be offered to patients at reduced costs. Since society will bear a large proportion of the costs associated with the complications from IVF treatment, there is a role for individual governments to assist in the uptake of mild strategies for IVF by increasing the accessibility of IVF in the public sector and encourage health insurance companies to provide full coverage of fertility treatments so that patients will be more willing to use milder strategies. It should also be emphasized that mild ovarian stimulation for IVF can only be introduced successfully in a setting with optimal laboratory performance. A reduced number of oocytes at the starting point for the IVF procedure could easily lead to too few good-quality embryos for transfer or cryostorage under suboptimal conditions, with major implications for overall success rates.
Eventually, ovarian stimulation might be replaced by in vitro maturation of oocytes. This technique aims at the in vitro culture of follicles after the retrieval of immature oocytes from unstimulated or minimally stimulated cycles. Consequently, it does not require the use of gonadotrophins for in vivo follicular growth and oocyte maturation (Barnes et al., 1995, 1996; Oktay et al., 1998). However, series published to date are small and even with the help of limited ovarian stimulation and hCG for oocyte maturation, pregnancy rates of 30% have only been obtained by transplanting multiple embryos, because implantation rates remain 10–15%. Insufficient data are currently available from follow-up studies to assess the safety of this technique for offspring (Chian et al., 1999, 2000; Rao and Tan, 2005).
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Conclusions |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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Evidence in favour of mild ovarian stimulation for IVF is accumulating in recent literature. Namely young, good responders and polycystic ovary syndrome patients may benefit from mild stimulation. However, an important concern regarding the use of a mild treatment strategy remains the reduction in the per cycle chance of pregnancy. Again, chances for IVF success should be balanced against patient discomfort, chances for complications and costs.
Data discussed in this review do not allow any conclusions to be drawn regarding the most optimal mild ovarian stimulation protocol. Increased understanding of the physiology of follicle development has also lead to more individualized stimulation approaches (Fauser et al., 2008). The development of at least more than one dominant follicle appears to be necessary to produce competing IVF treatment outcomes. However, a reduction in medication is feasible when the initiation of exogenous FSH is postponed until the end of the FSH window, or when FSH is being replaced by hCG or LH when ongoing follicle growth is no longer dependent on FSH.
By suppressing endogenous negative feedback mechanisms for the natural selection of a single dominant follicle by CC or aromatase inhibitors, the use of gonadotrophins can be limited even further. A combination of these strategies might lead to an even further reduction in medication (days) needed, while it may assist in the selection of a homogenous cohort of good quality and mature oocytes and achieve a more physiological response. The implementation of mild stimulation into standard clinical practice appears to be justified, although more studies are needed to further elaborate the various mild stimulation approaches.
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Funding |
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TOPAbstractIntroductionMethodsRelevant physiology of follicle...The development of milder...Implications of mild ovarian...Current status and future...ConclusionsFundingReferences |
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B.C.J.M. Fauser has received fees and grant support from the following companies: Organon, Schering Plough, Merck Serono, Ferring, Wyeth, Schering, Ardana, Andromed, Pantharei Bioscience and PregLem. N.S. Macklon has received fees and grant support from the following companies: Schering Plough, Merck Serono and Ferring.
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