The effect of pronuclear morphology on early development and chromosomal abnormalities in cleavage-stage embryos

Hum Reprod. 2003 Nov;18(11):2413-9. doi: 10.1093/humrep/deg458.


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.

MeSH terms

  • Adult
  • Blastocyst
  • Chromosome Aberrations / embryology*
  • Chromosome Aberrations / statistics & numerical data
  • Cleavage Stage, Ovum*
  • Embryo, Mammalian / physiology*
  • Embryonic and Fetal Development*
  • Female
  • Humans
  • Morula
  • Prognosis
  • Zygote / ultrastructure*