What we learned from extended culture of rejected day 3 cleavage stage embryos: A retrospective cohort study

Introduction : Embryologists and clinicians are uncomfortable when faced with decisions involving ongoing culture of poor-quality day 3 embryos; the true potential of a low-score embryo to yield a viable fetus is uncertain.

Aim: To test whether poor quality day-3 embryos can undergo successful blastulation and implantation.

Materials and Methods: A retrospective cohort study was conducted. Poor quality (rejected) embryos were further cultured when a good quality embryo was transferred on day 3 but the other embryos were graded poor and followed further, or when all embryos were graded poor and none were transferred on day 3. Once the embryos reached the blastocyst stage, they were followed up to day 6 from oocyte retrieval. 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 ther grade on day 3 significantly affected blastulation (P=0.01). A total of 96 embryos attained eligibility for fresh transfer or cryopreservation, only 6 of which resulted from a day 3 embryo scored<2. Of these, 51 were transferred resulting in 21 pregnancies: 16 clinical and 5 chemical. In summary, 694 cultured embryos yielded 16 clinical pregnancies, or 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; therefore the benefit of ongoing culture is questionable.