Comparison of two mainstream endometrial preparation regimens in vitrified–warmed embryo transfers after PGT

Which of the two mainstream endometrial preparation regimens, assisted natural cycle (NC) or hormone replacement treatment cycle (HRT), help frozen-thawed embryo transfer (FET) cycles after preimplantation genetic testing (PGT) achieve better clinical outcomes?This retrospective analysis included 3400 vitrified-warmed 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.No significant difference was observed between the assisted NC and HRT groups in terms of clinical pregnancy rate (51.6% versus 50.7%, P = 0.634), live birth rate (44.0% versus 43.4%, P = 0.746) or early miscarriage rate (12.6% versus 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% versus 51.9%, P 0.001) and pregnancy complication rate (20.2% versus 13.8%, P = 0.003) were significantly higher. The two groups were not statistically different with respect to gestational age, early preterm birth rate, fetal weight or fetal birth defect rate.For patients undergoing a 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.