Human Reproduction, Vol. 18, No. 11, 2413-2419,
November 2003
© 2003 European Society of Human Reproduction and Embryology
The effect of pronuclear morphology on early development and chromosomal abnormalities in cleavage-stage embryos
1 Instituto Valenciano de Infertilidad (IVI), Plaza Policía Local, Valencia and 2 Department of Paediatrics, Obstetrics and Gynaecology, University of Valencia, Valencia, Spain
3 To whom correspondence should be addressed at: Instituto Valenciano de Infertilidad, Policía Local 3, 46015 Valencia, Spain. e-mail: c.rubio{at}ivi.es
BACKGROUND: Pronuclear (PN) zygote morphology has been proposed as a useful tool for selecting the best embryos for transfer. METHODS: PN morphology was recorded in 888 zygotes and classified according to similar/different PN size [groups A (n = 816) and B (n = 72)] and to the number, distribution and synchrony of nucleolar precursor bodies (NPB): subgroup I, pronuclei with 3–4 polarized NPB; subgroup II, 5–7 synchronic polarized NPB or 7–10 NPB distributed randomly; and subgroup III, morphologies other than those of groups I or II. Embryo development and chromosomal abnormalities were evaluated for each PN pattern. RESULTS: In patients aged 
37 years, the number of zygotes reaching morula and blastocyst stage was significantly (P = 0.0003) higher in group A than in group B. In group A, the incidence of chromosomal abnormalities was significantly (P = 0.0247) lower than in group B, and significant differences were observed when pattern AI was compared with pattern AII (P = 0.0280), AIII (P = 0.0024), BIII (P = 0.0077) and total B (P = 0.0247). In patients aged >37 years, statistical differences among groups were not observed. CONCLUSIONS: In patients aged 37 years, zygotes with similar PN size and with polarized NPB present the best prognosis based on embryo development and the incidence of chromosomal abnormalities, whereas in patients aged >37 years, this correlation does not exist.
Key words: age/chromosomal abnormalities/ pronuclear morphology/nucleolar precursor bodies
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