Pregnancy outcome after blastocyst stage transfer comparing to early cleavage stage embryo transfer

Blastocyst transfer has been introduced as an alternative for improving the chance for in vitro fertilizations (IVF) implantation. The present study was to evaluate pregnancy rates when embryo transfer was performed either on day 2-3 (cleavage stage) or on day 4-5 (blastocyst stage). This randomized clinical trial included 118 infertile women. All the study subjects underwent controlled ovarian stimulation using a long protocol and randomized into two groups. BS group (n = 57), the culture was extended to day 5 (blastocyst stage) and in the CS-group (n = 61), embryo culture was continued to day 3 (cleavage stage). Ongoing pregnancies, abortion, implantation rate were evaluated. No significant differences were seen in the pregnancy rate between the two groups (33.3% in the BS group versus 27.9% in the CS group; p = 0.519). Abortion, implantation rate in two groups are not significant. Despite the lack of statistical difference between the two study groups, our data suggest that blastocyst transfer may be associated with a higher pregnancy and an overall better implantation rates. However, further studies with larger sample size are mandatory to confirm these findings.