The confounding effect of a live delivered pregnancy or not in the first fresh embryo transfer (ET) on the outcome of the first frozen ET

There are only a limited number of chromosomally normal embryos in a given cohort following oocyte retrieval and embryo development. Thus, the possibility exists that the live delivered pregnancy rate in the next ET using frozen-thawed embryos will be lower in women with successful live delivery than women who failed to have a success with the fresh ET because of a potential lower likelihood of having a normal embryo by the process of elimination. The present study was designed to corroborate or refute that hypothesis. Retrospective cohort comparison study. All first controlled ovarian hyperstimulation (COH) in vitro fertilization-ET (IVF-ET) cycles in women age <39 during a 10-year time period were reviewed. A subset of those having a subsequent frozen ET from that cohort of embryos were identified. This group was then stratified according to whether these women had a live delivery or not from the fresh ET cycle. The pregnancy and implantation rates in the subsequent frozen ET cycle were then compared in 3 age groups: <35, 36-39, and 40-42. All ETs were on day 3. Tabled 1Pregnancy rates from frozen ET based on achieving a live birth from the fresh ETPatients with previous pregnancy from fresh IVF cyclesPatients without previous pregnancy from fresh IVF cycleAge<3536-3940-42<3536-3940-42Number of transfers3208420953396145Clinical pregnancy/transfer46.6%36.9%30.0%38.8%32.1%20.7%% embryos implanted28.6%20.3%16.0%20.9%16.4%10.1%Live birth rate/transfer38.1%26.2%15.0%30.6%22.7%11.7% Open table in a new tab Though all age groups showed a trend for lower clinical and live delivered pregnancy rates in those failing to have a live baby in the fresh ET, the only comparison showing a statistically significant difference by chi-square analysis was the implantation rates in women aged <35 (p<0.01). The live delivered pregnancy rates in women <35 approached significance with p=0.08. One study found that the average number of chromosomally normal blastocysts available for transfer in women who averaged age 35 was 1.8, and another study found that there was an average of 1 live baby per IVF cycle considering the eventual transfer of all embryos created. These data refute the hypothesis that a successful pregnancy from the fresh ET has a negative effect on the chance of a live delivery from the frozen ET. These results could be explained by several theories: 1) some women tend to make more chromosomally normal embryos than others and are thus more fertile. 2) Failure to conceive on the first fresh ET may be related to other factors (endometrial or immunological) that persist in the frozen ET cycle. The fact that implantation and pregnancy rates showed a trend in all age groups to be lower in those who failed in the fresh ET suggests that COH adversely effecting implantation does not play a major role as to why a woman fails to conceive in a COH, IVF-ET cycle.