Comparison of ectopic pregnancy risk among transfers of embryos vitrified on day 3, day 5, and day 6

Objective To compare ectopic pregnancy risk among transfers of embryos vitrified on day 3, day 5, and day 6. Design Retrospective cohort study. Setting Academic tertiary-care medical center. Patient(s) A total of 10,736 pregnancies after 23,730 frozen-thawed embryo transfer (FET) cycles of in vitro fertilization/intracytoplasmic sperm injection from March 2003 to May 2015. Intervention(s) The ectopic pregnancy rate was compared among pregnancies resulting from transfers of embryos vitrified on day 3, day 5, and day 6. Generalized estimation equation regression models were used to calculate unadjusted and adjusted odds ratios and 95% confidence intervals for the association between ectopic pregnancy and selected patient and treatment characteristics. We studied this association in both the group that achieved pregnancy and the group that underwent an FET cycle. Main Outcome Measure(s) Odds of ectopic pregnancy. Result(s) The overall rate of ectopic pregnancy was 2.8% (304/10,736). Ectopic pregnancy rates after day-3, day-5, and day-6 vitrified embryo transfers were 3.1% (287/9,224), 2.0% (11/562), and 0.6% (6/950), respectively. After adjusting for confounders, the risks of ectopic pregnancy in day-3 and day-5 vitrified embryo transfers were both significantly higher than in day-6 vitrified embryo transfers. The associations were similar when we did calculations per cycle. Conclusion(s) In women undergoing FET, day-6 vitrified embryo transfer is associated with a significantly lower risk of ectopic pregnancy than both day-3 and day-5 vitrified embryo transfers.