Pronuclear morphology has been reported as a good tool for studying embryo development and euploidy. Comparing two groups of women with different aneuploidy risk, women more than 38 years old (n = 28) known to be at high risk of aneuploidy, and women under 30 years old (n = 35), this study investigated whether pronuclear morphology could be used routinely as an alternative to preimplantation genetic screening (PGS) in countries where PGS is prohibited. Pronuclear morphology was evaluated for 301 zygotes and related to embryo quality and pregnancy outcome. For the older women, an increased frequency of zygotes with abnormal polar body and pronuclei alignment was observed, i.e. type gamma, with 93% aneuploidy risk (26.0 versus 15.1% P < 0.05) and fewer zygotes with a good development prognosis (36.4 versus 47.8%; P < 0.05). A1alpha configuration was associated with good implantation rate and was not related to day 2 embryo quality. This configuration was less frequent in the group of women more than 38 years old and among non-pregnant women under 30 years, compared with pregnant women under 30 years old. Pronuclear morphology seemed linked to age, but not associated with embryo quality. A larger study allowing correlation analysis is necessary to confirm the value of these criteria and the link to a woman's age.

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