Zygote score and status 1 or 2 days after cleavage and assisted reproduction outcome

To determine whether pronuclear morphology is a useful additional criterion when selecting embryos for transfer.

A modified Tesarik and Greco scoring system was used in this retrospective study to assess the pronuclear morphology of 883 zygotes from 214 in vitro fertilization or intracytoplasmic sperm injection cycles. Pronucleus size and presence of cytoplasmic halo were also noted. Embryo selection was performed on Day 2 or 3 following oocyte retrieval. The chi2, analysis of variance, Kruskal-Wallis, and Fisher exact tests were used where appropriate.

A stepwise logistic regression revealed that a better embryo quality was associated with both pattern 0 of the scoring system and pronuclei of equal size on Days 2 or 3. Higher pregnancy and multiple gestation rates were obtained when at least 1 embryo classified as pattern 0 was included in the set of embryos transferred.

Combined with embryo morphology evaluation on Days 2 and 3, a scoring system based on pronuclear morphology seems to provide a good criterion when selecting embryos for transfer.