Abstract

OBJECTIVE: Ectopic pregnancy can be a life-threatening complication of in vitro fertilization (IVF) and is estimated to occur in 2-5% of cycles. It has been proposed that embryo transfer (ET) at the blastocyst stage may decrease the incidence of ectopic pregnancy compared to cleavage stage ET, but the few small studies in the literature that have investigated this question have been inconclusive. The objective of this study was to determine the risk of ectopic pregnancy following day 5 blastocyst ET compared to cleavage stage ET. DESIGN: Retrospective cohort study. MATERIALS AND METHODS: All patients who achieved pregnancy following fresh IVF at our center from January 1, 2000 through December 31, 2008 were identified. The data collected included age, IVF cycle number, cycle type, and pregnancy outcome. Repeated measures log-binomial regression was used to calculate risk ratios (RR) and 95% confidence intervals (CI). RESULTS: From 2000 through 2008, 13,571 pregnancies occurred in 8,420 women following fresh IVF cycles. The majority of these pregnancies occurred in fresh homologous IVF cycles (93.2%), and the remainder were fresh oocyte recipient cycles (6.8%). Mean patient age was 36.4 years and median cycle number was 2.0. Of these 13,571 IVF pregnancies, 171 (1.3%) were ectopics diagnosed in 169 women. Of these ectopic pregnancies, 159 (93.0%) followed day 3 ET, and 12 (7.0%) followed day 5 ET. The crude RR of ectopic pregnancy following blastocyst ET compared with cleavage stage ET was 0.59 (CI 0.33-1.05). The age-adjusted RR was unchanged. No other variables (including cycle number and cycle type) had an appreciable effect on the RR. CONCLUSIONS: Our findings suggest that blastocysts are less likely to implant outside the endometrial cavity than cleavage stage embryos. This could be due to the shorter time between ET and implantation for blastocysts compared to day 3 embryos. This report represents the largest study to date evaluating the risk of ectopic pregnancy following blastocyst ET compared to cleavage stage ET.

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