First trimester pregnancy loss following fresh and frozen in vitro fertilization cycles

To determine if there is an increased risk of first trimester pregnancy loss in frozen embryo transfer cycles as compared to fresh cycles following in vitro fertilization (IVF). Retrospective cohort study using data from Centers for Disease Control and Prevention National ART Surveillance System for 2007-2012. Multivariable log binomial regression, stratified by maternal age (< 30, 30-34, 35-37, 38-40, >40 years), was performed to compare age- specific risk of first trimester pregnancy loss between fresh and frozen embryo transfers. The main analysis included fresh cycles (n=203,970) and frozen cycles for which maternal age at oocyte retrieval could be ascertained (n=45,660) that resulted in a pregnancy. A subgroup analysis was performed to compare miscarriage risks of similar quality embryos between fresh (n=203,970) and frozen cycles (n=7,885). Frozen cycles for the subgroup analysis were restricted to those for which their originating fresh cycle had not had an embryo transfer (i.e. the embryo(s) transferred during the frozen cycle were the first embryos transferred from the originating retrieval). There was an increased risk of first trimester loss in pregnancies achieved after frozen embryo transfers versus fresh cycles and the adjusted relative risk remained significant among women less than 37 years of age: <30 years: 14.9% vs. 8.2%, aRR=1.37, 95% CI=1.29-1.44; 30-34 years: 16.1% vs. 10.0%, aRR=1.23, 95% CI=1.18-1.27; 35-37 years: 19.3% vs. 13.7%, aRR=1.14, 95% CI=1.09-1.19. In the sub-analysis, the risk of miscarriage was significantly higher in frozen cycles only among women less than 30 years of age: 12.0% vs. 8.2%, aRR=1.16, 95% CI=1.04-1.32. There was an increased risk of first trimester loss in frozen cycles compared to fresh cycles in younger women. This risk, however, which could be ascribed to lower embryo quality in frozen cycles, was reduced in the subgroup analysis that compared similar quality embryos from fresh and frozen cycles.