Will Freezing All Embryos Achieve IVF's Holy Grail?

Conventional in vitro fertilization–embryo transfer (IVF-ET) involves several steps, from ovarian stimulation to fertilization of retrieved oocytes, transfer of one to two embryos into the uterus, and cryopreservation of remaining embryos for future nonstimulated cycles. An alternative approach is “freeze-all” IVF-ET, where all embryos obtained during the stimulated cycle are frozen for transfer in subsequent nonstimulated cycles. This approach has been hypothesized to provide a more physiologic environment for embryo implantation (because the endometrium has not been perturbed by high concentrations of estradiol associated with ovarian stimulation), resulting in higher live birth rates.

To directly compare pregnancy outcomes with conventional versus freeze-all IVF-ET, investigators in China randomized 2157 ovulatory infertile women undergoing their first IVF-ET cycle to either strategy. Live birth rates in the conventional and freeze-all IVF-ET groups were 50% and 49%, respectively (P=0.50). Likelihood of ovarian hyperstimulation syndrome (OHSS) was lower with freeze-all IVF-ET (0.6% vs. 2.0%; relative risk, 0.3, P=0.005). Obstetric and neonatal outcomes were similar in both groups.

In a related study, 782 Vietnamese ovulatory women undergoing their first or second IVF-ET cycle were randomized to conventional or freeze-all IVF-ET. Live birth rates were similar in both groups (32% and 34%), as was risk for OHSS (1.0% and 0.8%).