Natural cycle or hormone replacement IVF for women with regular cycles?

This study compared natural cycle versus hormone replacement in vitro fertilization (IVF) for infertile women with regular menstrual cycles. It found that natural cycle IVF led to higher birth rates.

Frozen embryo IVF is a treatment for infertility in which eggs are removed from the woman and fertilized. The embryo(s) are frozen and implanted in a later cycle. For implantation to be successful, the lining of the womb (endometrium) must be ready.

After a woman ovulates (releases an egg), a structure called the corpus luteum (CL) develops in her ovary. The CL releases hormones that prepare the womb lining for implantation. If the woman becomes pregnant, the CL supports the pregnancy throughout the first trimester. The CL varies hormone levels based on signals it receives from the embryo(s).

In natural cycle (NC) IVF, the woman’s menstrual cycle is tracked and an embryo is implanted after she ovulates. In hormone therapy (HT) IVF, the woman is injected with hormones that mimic the menstrual cycle. No CL develops during HT-IVF. Instead, the woman takes hormone injections throughout the first trimester. 

It is unclear which form of IVF is better for young women with regular menstrual cycles.

This study used records from 1,846 women with infertility. They were under age 35 and had menstrual cycles between 25 and 35 days. This was the patients’ first cycle of IVF. 308 patients had NC, while 1,530 had HT. The patients were followed for one year after the frozen embryo transfer. Patients transferred one or two embryos.

The HT and NC groups had a similar per-embryo implantation rate (52.4% vs. 54.0%). They were had similar rates of pregnancy conformed on ultrasound (65.5% vs. 69.8%). However, patients in the HT group had significantly higher rates of miscarriage (13.69% vs. 8.37%). Compared to the HT group, patients in the NC group had significantly higher rates of live birth (55.11% vs. 61.73%).

This study found that NC-IVF resulted in higher rates of live birth than HT-IVF for young women with regular cycles.

The average age of women was 28.4 years (NC) and 28.2 years (HT), which is younger than most patients seeking IVF. Also, patients were assigned to treatment based on their doctor’s recommendation, so the two groups had different characteristics.