Abnormal implantation after fresh and frozen in vitro fertilization cycles

Abstract

Objective: To determine whether fresh embryo transfers are at a higher risk of abnormal implantation compared with frozen embryo transfers while accounting for the embryo stage at transfer.

Design: Retrospective cohort study.

Setting: Not applicable.

Patient(s): We used data from the Society for Assisted Reproductive Technologies to identify all fresh and frozen autologous IVF cycles from 2004-2013 resulting in a positive pregnancy test. The cycles were parameterized into a four-level predictor of [1] fresh blastocyst transfer, [2] fresh non-blastocyst transfer, [3] frozen blastocyst transfer, and [4] frozen non-blastocyst transfer.

Intervention(s): None.

Main outcome measure(s): We examined a composite outcome of abnormal implantation, defined as biochemical pregnancy, ectopic/heterotopic pregnancy, and first-trimester pregnancy loss. Regression modeling was performed with repeated measures multivariable logistic regression, adjusted for age, parity, number of embryos transferred, infertility diagnosis, and calendar year of treatment.

Result(s): Of 509,938 cycles analyzed, 31.8% resulted in abnormal implantation. Compared with a fresh blastocyst transfer, a fresh non-blastocyst transfer had a 22% increase risk of abnormal implantation, a frozen blastocyst transfer had a 36% increase risk, and a frozen non-blastocyst transfer had a 57% increase risk. When individual outcomes were analyzed, fresh embryo transfers had a lower risk of biochemical pregnancy and pregnancy loss but a higher risk for ectopic/heterotopic pregnancy.

Conclusion(s): Fresh blastocyst transfers had the lowest overall risk of abnormal implantation but a higher risk of ectopic/heterotopic pregnancy. Although embryo cryopreservation is indicated in certain treatment cycles, elective embryo cryopreservation may not be the optimal strategy to adopt for all cycles.

Keywords: Abnormal implantation; embryo cryopreservation; in vitro fertilization.