Study question

In natural frozen-thawed embryo transfer (FET) cycles, does luteal phase support (LPS) with progesterone improve cycle outcomes?

Summary answer

Vaginal progesterone gel supplementation significantly improves pregnancy rate in natural frozen-thawed embryo transfer (FET) cycles.

What is known already

Luteal phase support (LPS) with progesterone improves outcomes in fresh controlled ovarian hyperstimulation(COH) in vitro fertilization(IVF) cycles and high dose progesterone supplementation in hormonally controlled FET cycle has resulted in higher clinical pregnancy rate. However, there is no consensus about the possible benefit of LPS in natural FET cycles.

Study design, size, duration

This retrospective cohort study included 432 women undergoing FET in natural cycles without hCG between Jan 2010 and Dec 2012.

Participants/materials, setting, methods

By ultrasound examination and monitoring of serum hormone levels, exact ovulation day was assessed. The cryopreserved embryos were transferred 3 days after ovulation. One hundred patients (Group A) received daily vaginal progesterone gel starting from the day of embryo transfer and 332 patients (Group B) did not receive it.

Main results and the role of chance

In each group, age, AMH level, number of transferred embryos and percentage of top quality embryos reflected no differences. Pregnancy rate was significantly higher in the group that received progesterone than in the other group [41.0%(41/100) vs. 29.2%(97/332), P=0.013]. There was no significant difference between two groups in the spontaneous abortion rate. Ongoing pregnancy rate was also significantly higher in LPS group [40.0%(40/100) vs. 28.3%(94/332), P=0.009].

Limitations, reasons for caution

This is a retrospective study. A prospective randomized study would have minimized potential limitations.

Wider implications of the findings

In general, endogenous production of progesterone is sufficient to support implantation in a natural cycle of fertile women. In this case additional progesterone does not change IVF outcomes. In our study, pregnancy rate was improved by LPS in natural FET cycle, it is probably because the women who undergo IVF cycles are often subfertile, and they may have suboptimal progesterone level. Therefore, even though in natural cycle clinician should consider LPS to women undergoing FET.