Time from oocyte retrieval to frozen embryo transfer in the natural cycle does not impact reproductive or neonatal outcomes.

Objective: To determine if the time from oocyte retrieval to frozen embryo transfer (FET) in the natural cycle affects reproductive or neonatal outcomes.

Design: Retrospective cohort.

Setting: Not applicable.

Patient(s): Five hundred and seventy-six consecutive freeze-all cycles from January 2011 to December 2018 followed by natural cycle FET of a single blastocyst.

Intervention(s): None.

Main Outcome Measure(s): Primary outcome of live birth; secondary outcomes of preterm delivery (24-37 weeks) and small for gestational age (SGA) with a multivariable logistic regression performed with adjustment for age, infertility diagnosis, ovulatory trigger type, and preimplantation genetic testing (PGT).

Result(s): Before adjustment for confounding, we found a statistically significantly different live-birth rate (57.7% vs. 48.6%) for natural cycle FET occurring in the first versus second menstrual cycle, respectively. In a multivariate analysis, performing a natural cycle FET of a single blastocyst in the second compared with the first menstrual cycle did not statistically significantly impact the odds of live-birth rate. After adjustment for age, diagnosis, and ovulatory trigger type, only PGT was associated with statistically significantly increased odds of live birth compared with no PGT. There were no differences in the incidence of SGA (male, 6.6% vs. 2.3%; female, 9.8% vs. 11.1%) or preterm delivery (1.6% vs. 5.6%) between both groups.

Conclusion(s): Performing a natural cycle FET of a single blastocyst in the second compared with the first menstrual cycle after ovarian stimulation did not statistically significantly impact the odds of live birth or neonatal outcomes.