Natural cycle versus artificial cycle in frozen–thawed embryo transfer: a randomized prospective trial

Objective: The purpose of this study was to investigate whether there is a difference in pregnancy outcome between modified natural cycle FET (NC-FET) and artificial cycle FET (AC-FET) in women who all had regular menstrual cycles.
Materials and Methods: 170 patients who met the inclusion criteria and had at least two cryopreserved embryos were included in a prospective randomized controlled trial. 85 patients were randomized based on Bernoulli distribution into the following two groups: 1) modified NC-FET using human chorionic gonadotropin (hCG) for ovulation induction and 2) AC-FET in which endometrial timing was programmed with estrogen and progesterone. The main studied outcome measure was the clinical pregnancy rate per cycle.
Results: No significant differences were found between the two groups with regard to the chemical, clinical, and ongoing pregnancy rates (48.2% versus 45.9%, P ˃ 0.05; 38.9% versus 35.3%, P ˃ 0.05; and 37.6% versus 34.1%, P ˃ 0.05, respectively), as well as the live birth or miscarriage rates per cycle (35.3% versus 31.8%, P ˃ 0.05; and 1.2% versus 1.2%, P ˃ 0.05, respectively).
Conclusion: These findings suggest that although both FET protocols are equally effective in terms of pregnancy outcomes in women with regular menstrual cycles, NC-FET is more favorable because it requires no medications, has no adverse events, and has a significant cost reduction.
Keywords: Frozen-thawed embryo transfer, Artificial cycle, Natural cycle, Clinical pregnancy rate