Comparison of assisted natural versus hormone replacement treatment cycles in 3400 frozen-thawed embryo transfers after preimplantation genetic testing

Abstract Research question Which of the two mainstream endometrial preparation regimens, assisted natural cycle (NC) and hormone replacement treatment cycle (HRT), can help frozen-thawed embryo transfer (FET) cycles after preimplantation genetic testing (PGT) achieve better clinical outcomes? Design This retrospective analysis included 3400 frozen-thawed single blastocyst transfer cycles after PGT from January 2011 to November 2020, and involved 2332 patients with regular menstrual cycles. The decision to proceed with an assisted NC (n=827) or HRT (n=2573) before FET was reached based on a combination of patient preference and physician guidance. Clinical pregnancy rate, live birth rate, early miscarriage rate, and obstetric outcomes were compared. Results No significant difference was observed between the assisted NC and HRT groups in terms of clinical pregnancy rate (51.6% vs. 50.7%, P=0.634), live birth rate (44.0% vs. 43.4%, P=0.746), and early miscarriage rate (12.6% vs. 12.0%, P=0.707). Multivariate analysis indicated that the endometrial preparation protocol was not an independent factor for a clinical pregnancy or live birth. In the HRT group, the caesarean section rate (64.7% vs. 51.9%, P Conclusions For patients undergoing an PGT-FET cycle involving a single blastocyst transfer, using assisted NC and HRT for the endometrial preparation could lead to comparable rates of clinical pregnancy and live birth. Additionally, NC is safer than HRT in terms of avoiding pregnancy complications and adverse obstetric outcomes.