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Human Reproduction Update Advance Access published online on October 15, 2008
Human Reproduction Update, doi:10.1093/humupd/dmn045
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© The Author 2008. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

The risk of monozygotic twins after assisted reproductive technology: a systematic review and meta-analysis

S. Vitthala, T.A. Gelbaya1, D.R. Brison, C.T. Fitzgerald and L.G. Nardo

Department of Reproductive Medicine, St Mary’s Hospital, Whitworth Park, Manchester M13 0JH, UK

To whom correspondence should be addressed at: 1 Correspondence address. Fax: +44-0161-224-0957; E-mail: tarek.gelbaia{at}cmmc.nhs.uk/tagelbaya{at}yahoo.co.uk

BACKGROUND: It is estimated that there is at least a 2-fold rise in the incidence of monozygotic twinning after assisted reproductive technology compared with natural conception. This can result in adverse pregnancy outcomes.

METHODS: We searched MEDLINE, EMBASE and SCISEARCH for studies that estimated the risk of monozygotic twinning and its association with any particular assisted reproductive technique. Monozygotic twinning was defined by ultrasound or Weinberg criteria. A meta-analysis of the proportion of monozygotic twins was performed using both fixed and random effects models.

RESULTS: The search revealed 37 publications reporting on the incidence of monozygotic twins after assisted reproductive techniques. Twenty-seven studies met the inclusion criteria and were included in the meta-analysis. The summary incidence of monozygotic twins after assisted conception was 0.9% (0.8–0.9%). The incidence of monozygotic twins in natural conception is 0.4%. Blastocyst transfer and intracytoplasmic sperm injection are associated with 4.25 and 2.25 times higher risk of monozygotic twins.

CONCLUSIONS: The risk of monozygotic twins in assisted conception is 2.25 times higher than the natural conceptions. Larger studies reporting on monozygotic twinning following single-embryo transfer or after post-natal confirmation of zygosity with DNA analysis are warranted before definitive conclusions can be drawn and guidelines produced. In order to provide adequate pre-conceptional counselling, it is important to monitor the incidence of monozygotic twins in both natural and assisted conceptions. We suggest building a national multiple pregnancy database based on accurate diagnosis of zygosity.

Key words: monozygotic and monochorionic twins / in vitro fertilization / intracytoplasmic sperm injection / blastocyst / assisted hatching

Received on April 13, 2008; revised September 2, 2008; accepted on September 16, 2008


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