Transferring embryos on day 2 versus day 3 in women with low fertilization rates does not affect pregnancy and implantation rates

Abstract

The timing of embryo transfer on day 2 (D2) or day 3 (D3) has been a topic of controversy. Studies on preferential embryo transfer on D2 versus D3 in women with a high yield of fertilized oocytes, comparing pregnancy and implantation rates, have led to conflicting results [1]. However, the potential difference in outcomes of D2 versus D3 embryo transfer in women with a low yield of fertilized oocytes has not been looked at thoroughly. To evaluate the differences, if any, in pregnancy and implantation rates when embryo transfer occurs on D2 versus D3. Design: Retrospective cohort. Setting: Academic fertility center. Interventions: A total of 94 IVF cycles from 87 women were analyzed. Women with a low yield of fertilized oocytes (≤2 2PN stage zygotes) who had their embryo transfer on D2 or D3 were included in the study. Exclusion criteria included: Donor oocyte, pre-implantation genetic testing, and gestational carrier cycles, as well as women who yielded >2 fertilized oocytes. Cycles were categorized into two groups: cycles during which embryo transfer had occurred on D2 (Group 1) or D3 (Group 2). Positive pregnancy test (serum β-hCG concentration >6 IU/L) per IVF cycle (PPT), clinical pregnancy rate (CPR) and implantation rate (number of sacs seen on US over the number of embryos transferred in cycles with β-hCG>6). Mann-Whitney U-test and χ2-test were used as appropriate. P<0.05 was considered significant. Table 1 summarizes the baseline and cycle characteristics of the two groups. Patients having their embryo transfer on D2, when compared to those who had a D3 embryo transfer, experienced similar PPT (31.9 vs. 29.8%, p=0.82; respectively). Most importantly, CPR (23.4 vs. 23.4%, p=1.00; respectively) and implantation rate (46.7 vs. 50.0%, p=0.81; respectively) were comparable between the two groups (Figure 1A-B). Our findings suggest that transferring embryos on D2 versus D3 in women with a low fertilization rate does not seem to affect CPR or implantation rates. These results indicate that there can be some flexibility in scheduling the day of transfer at the convenience of both the patient and the center.