Endometrial thickness affects live birth rates following embryo transfer

Reduced endometrial thickness contributes to a dramatic decrease in the chance of live birth following embryo transfers, a study reports. In contrast, live birth rates markedly improve with thicker endometrium.

The study used national data from Autologous in vitro fertilization (IVF) embryo transfer (ET) and frozen embryo transfer (FET) cycles from the Canadian Assisted Reproductive Technology Registry Plus (CARTR Plus) database. In total, 43,383 fresh and 53,377 frozen transfers were included in the analysis.

The mean endometrial thickness was 10.2 mm in fresh IVF-ET and 9.6 mm in the FET cycles.

Greater endometrial thickness in fresh IVF-ET cycles was associated with younger age and higher parity, higher peak oestradiol levels, and higher numbers of oocytes at retrieval and embryos available for transfer or cryopreservation; favourable clinical pregnancy rates, live birth rates, and mean term singleton birth weights; and a decrease in pregnancy loss rates. However, live birth rates plateaued after endometrial thickness exceeded 10–12 mm.

In FET cycles, endometrial thickness was linked to age at cycle start and mean parity, as well as the mean number of prior embryo transfers. Live birth rates plateaued beyond an endometrium thickness of 7–10 mm.

The favourable live birth rates observed with increasing endometrial thickness were not modified by patient age, timing of embryo transfer (eg, cleavage stage vs blastocyst stage), or the number of oocytes at retrieval.