What we learned from extended culture of 'rejected' day-3 cleavage stage embryos: a prospective cohort study

Background: To test whether poor quality day-3 embryos can undergo successful blastulation and implantation. Methods: A prospective cohort study was conducted. Whether or not a good quality embryo was transferred on day-3, poor quality (rejected) embryos were further cultured and followed. The clinical outcome of each embryo was assessed. Results: A total of 694 rejected embryos (from 205 patients) were included, with a blastulation rate of 21.2% (147 embryos) compared to 64.2% general blastulation rate reported by our laboratory (P < 0.01). In a multivariate logistic regression model, only their grade on day-3 significantly affected blastulation (P = 0.01). A total of 97 embryos attained eligibility for fresh transfer or cryopreservation, only 6 of which resulted from a day-3 embryo scored < 2. Of these, 52 were transferred, resulting in 21 pregnancies (16 clinical and 5 chemical). In summary, 694 cultured embryos yielded 16 clinical pregnancies; a 2.3% clinical pregnancy rate. Conclusions: Low score day-3 embryos can result in successful blastulation and clinical pregnancies. However, the normal blastulation rate is poor.