Pregnancy and neonatal outcomes of small follicle–derived blastocyst transfer in modified natural cycle in vitro fertilization

Objective: To compare the efficacy and safety of blastocyst transfer derived from small follicles (SF; ≤10 mm) and large follicles (LF; ≥11 mm). Design: Retrospective cohort study. Setting: Private clinic. Patient(s): Patients (n = 1,072) 30–40 years old who underwent blastocyst transfer (BT; n = 1,247) between January 2012 and December 2014. Intervention(s): Oocytes retrieved during a modified natural cycle from both LF and SF were fertilized by a conventional method or intracytoplasmic sperm injection. The blastocysts were frozen, thawed, and transferred one by one in the following spontaneous ovulatory cycles or hormone replacement cycles. Main Outcome Measure(s): BT resulted in live births and major congenital anomalies. Result(s): SF-derived BTs (n = 597) yielded 55 chemical abortions (9.2%), 73 clinical abortions (12.2%), and 261 live births (43.8%), whereas LF-derived BTs (n = 650) yielded 71 chemical abortions (10.9%), 73 clinical abortions (11.2%), and 311 live births (47.9%). These incidences were not statistically different between SF- and LF-derived BTs. The incidence of abnormal karyotypes was also not statistically different between SF- and LF-derived spontaneous abortions (71% [39/55] vs. 72% [40/55], respectively). The incidence of major congenital anomalies in neonates did not differ between SF- and LF-derived pregnancies (1.5% and 1.3%, respectively; relative risk = 1.10, 95% confidence interval [0.55–3.21]). Conclusion(s): SF-derived BT is as efficacious and safe as LF-derived BT.