• C Oatway, J Gunby, and S Daya.
• Obstetrics and Gynaecology, University of Sheffield, 136 Cobden View Rd, Crookes, Sheffield, UK, S10 1HS.
• Cochrane Db Syst Rev. 2004 Jan 1 (2): CD004378.

BackgroundEmbryo transfer (ET) was traditionally performed two days after oocyte retrieval; however, developments in culture media have allowed embryos to be maintained in culture for longer periods. Delaying transfer from day two to day three would allow for further development of the embryo and might have a positive effect on pregnancy outcomes.ObjectivesTo determine if there is any difference in live birth and pregnancy rates when ET is performed on day three, compared with day two, in infertile couples undergoing treatment with in vitro fertilization (IVF), including intracytoplasmic sperm injection (ICSI).Search StrategyWe searched the Cochrane Menstrual Disorders & Subfertility Group trials register (17th December 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 1, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and Biological Abstracts Databases (1980 to 2003), the National Research Register (NRR), the Medical Research Council's Clinical Trials Register, the NHS Centre for Reviews and Dissemination, citation lists of relevant publications, review articles and included studies, as well as abstracts of appropriate scientific meetings.Selection CriteriaRandomized controlled trials that compared day three versus day two embryo transfer after oocyte retrieval during an IVF or ICSI treatment cycle in subfertile couples.Data Collection And AnalysisTwo reviewers independently assessed trial quality and extracted data. Study authors were contacted for additional information. The primary outcome measures were live birth rate and ongoing pregnancy rate.Main ResultsTen studies involving 2027 women were included, but only three studies reported live birth and four reported ongoing pregnancy rates. The pooled odds ratios (day three compared to day two) were 1.07, 95% CI 0.84 to 1.37 for live birth and 1.05, 95% CI 0.83 to 1.32 for ongoing pregnancy. From ten studies, the pooled odds ratio for clinical pregnancy was 1.26, 95% CI 1.06 to 1.51. Sub-group analysis revealed that this advantage occurred in those undergoing ICSI cycles. A higher miscarriage rate with day 3 ET in ICSI cycles works to negate the increased clinical pregnancy rate, in agreement with the finding of no significant difference between treatments in live birth rate.Reviewers' ConclusionsAlthough an increase in clinical pregnancy rate with day three embryo transfer was demonstrated, at present there is not sufficient good quality evidence to suggest an improvement in live birth when embryo transfer is delayed from day two to day three.

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