Evaluation of pronuclear morphology as the only selection criterion for further embryo culture and transfer: results of a prospective multicentre study

BACKGROUND: The aim was to study zygote evaluation based on pronuclear morp hology under the German embryo protection law, according to which only a ma ximum of three zygotes are allowed to be cultured for embryo transfer. METH ODS: In this prospective multicentre study, a total of 512 treatment cycles was performed at 10 centres, between November 1999 and October 2000. Zygot es were classified into seven patterns (OA, OB and 1-5). Pattern OA and OB zygotes were preferentially used for further culture and transfer. RESULTS: Cycles with transfer of at least one embryo derived from pattern OB, but n ot pattern OA, resulted in significantly higher pregnancy (37.9%) and impla ntation rates (20.5%) compared with non-pattern OB cycles (26.4 and 15.7%; P < 0.05 and P < 0.01 respectively). In younger patients (aged less than or equal to 35 years), significantly more OB zygotes were available for trans fer than in older patients (34.2 versus 25.8%; P < 0.005). CONCLUSIONS: Fro m these data, it is concluded that evaluation of pronuclear morphology is b eneficial, especially for countries with legal restrictions regarding embry o selection.