Double transfer of embryos in in vitro fertilization, or is there a delayed receptivity of the endometrium?

Sixty-seven in vitro fertilization (IVF) patients who underwent ultrasonically guided oocyte pickup (OPU) after induction of superovulation with human menopausal gonadotropins were submitted to two different protocols of embryo transfer. In the first group of 33 patients, four to five embryos were transferred to the uterus 48 hr after OPU. In the second group of 34 patients two to three embryos were transferred at 48 hr after OPU and two other embryos were transferred after freezing and thawing 48 hr later (96 hr after OPU). The pregnancy rate achieved in the double embryo transfer (ET) protocol was significantly higher than in the single-ET protocol (32.4 vs. 18.2%, respectively; P less than 0.05).