Evaluation of pronuclear morphology as the only selection criterion for further embryo culture and transfer: results of a prospective multicentre study M.Montag1 and H.van der Ven on behalf of the German Pronuclear Morphology Study

BACKGROUND: The aim was to study zygote evaluation based on pronuclear morphology under the German embryo protection law, according to which only a maximum of three zygotes are allowed to be cultured for embryo transfer. METHODS: In this prospective multicentre study, a total of 512 treatment cycles was performed at 10 centres, between November 1999 and October 2000. Zygotes were classified into seven patterns (0A, 0B and 1–5). Pattern 0A and 0B zygotes were preferentially used for further culture and transfer. RESULTS: Cycles with transfer of at least one embryo derived from pattern 0B, but not pattern 0A, resulted in significantly higher pregnancy (37.9%) and implantation rates (20.5%) compared with non-pattern 0B cycles (26.4 and 15.7%; P < 0.05 and P < 0.01 respectively). In younger patients (aged ≤35 years), significantly more 0B zygotes were available for transfer than in older patients (34.2 versus 25.8%; P < 0.005). CONCLUSIONS: From these data, it is concluded that evaluation of pronuclear morphology is beneficial, especially for countries with legal restrictions regarding embryo selection.