Purpose: To evaluate the differences in implantation and pregnancy rates when embryo transfer occurs on D2 versus D3 in women with a low yield of fertilized oocytes.
Methods: A total of 156 IVF/ICSI cycles from 141 women at an academic fertility center were analyzed in a retrospective fashion. Women with a low number of fertilized oocytes (≤ 2 two pronuclei (2PN) stage zygotes) who had their fresh embryo transfer on D2 or D3 were included in the study. Positive pregnancy test per IVF cycle (PPT), clinical pregnancy rate (CPR), spontaneous abortion rate (SABR), and implantation rate (IMPR) were the main outcome measures assessed. Mann-Whitney U test and χ2 test were used as appropriate. A generalized linear mixed effect model adjusted for relevant covariates was conducted. P < 0.05 was considered significant.
Results: Patients having their embryo transfer on D2, when compared to those who had a D3 embryo transfer, experienced similar PPT [30.8 vs. 28.2%, respectively; adjusted OR (95%CI): 0.49 (0.16, 1.52)], CPR [26.9 vs. 25.6%, respectively; adjusted OR (95%CI): 0.44 (0.12, 1.67)], and IMPR [17.3 vs. 16.7%, respectively; adjusted β (95%CI) - 5.6% (- 15.0, 3.9)].
Conclusion: Our findings suggest that transferring embryos on D2 versus D3 in women with a limited number of 2PN stage zygotes does not affect early pregnancy outcomes. 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.
Keywords: 2PN; Embryo transfer; IVF; Implantation rate; Pregnancy outcomes.