Freeze-all at the blastocyst or bipronuclear stage: a randomized clinical trial

Abstract

Objective: To compare outcomes for patients randomized to have all embryos cryopreserved at the blastocyst stage or at the bipronuclear stage with subsequent post-thaw culture to the blastocyst stage.

Design: Randomized controlled trial.

Setting: Private fertility center.

Patient(s): This study included 140 women, age 18-40 years, with at least eight antral follicles, and day 3 FSH <10 IU/L undergoing IVF.

Intervention(s): After oocyte retrieval, subjects were randomized to have entire embryo cohorts cryopreserved at either the bipronuclear stage (2PN Cryo group) or at the blastocyst stage (Blast Cryo group).

Main outcome measure(s): Ongoing pregnancy (viable fetal heart motion at 10 weeks' gestation) per oocyte retrieval through the first transfer attempt.

Result(s): No significant differences were observed between the two study groups in age at retrieval, body mass index, antral follicle count, day 3 FSH level, or IVF cycle parameters. No significant differences were observed in ongoing pregnancy rate per retrieval (62.0%; 95% confidence interval [CI], 50.3%-72.4%) in the 2PN Cryo group; and 55.1%; 95% CI, 42.6%-67.1% in the Blast Cryo group), implantation rate (60.0% vs. 62.7%), ongoing pregnancy rate per thaw (62.0% vs. 59.4%), ongoing pregnancy rate per transfer (67.7% vs. 69.1%), and the cumulative ongoing pregnancy rate per retrieval from all thaws to date of embryos derived from the study retrieval cycle (64.8% vs. 60.9%).

Conclusion(s): Freeze-all at the blastocyst stage or at the bipronuclear stage has similar efficacy and IVF outcomes. The choice between them may depend primarily on logistical factors.

Clinical trial registration number: NCT01247987.

Keywords: In vitro fertilization; blastocyst transfer; embryo cryopreservation; embryo vitrification; frozen embryo transfer.