The natural cycle protocol of endometrial preparation for frozen embryo transfer decreases the miscarriage rate in women with recurrent pregnancy loss.

Objective: To investigate whether different endometrial preparation methods lead to different results.

Design: Retrospective cohort study.

Patients: Women with recurrent pregnancy loss undergoing frozen embryo transfer (FET).

Interventions: Natural cycle (NC) protocol (n = 111) with no drug or human chorionic gonadotropin (HCG) used for endometrial preparation, vs. the hormone replacement therapy (HRT) protocol (n = 797) with estrogen or gonadotropin releasing hormone agonist (GnRH-a) plus estrogen used for endometrial preparation.

Main outcome measures: Miscarriage rate and live birth rate (LBR).

Results: Compared to women in the HRT protocol, women undergoing NCs had fewer previous FET cycles, lower antral follicle counts (AFCs), fewer oocytes retrieved and a thicker endometrium on the day of progesterone administration. Women in the HRT group had a higher miscarriage rate (29.4% vs. 17.2%) and a lower LBR (37% vs. 46.9%) than the rates of women in the NC group. Univariate analysis showed that female age also had a negative association with the miscarriage rate. Logistic regression indicated that endometrial preparation using the NC protocol was linked to a decreased likelihood of miscarriage.

Conclusions: The NC protocol decreased the miscarriage rate and increased the LBR for patients with recurrent pregnancy loss compared with the HRT protocol.