Normal chromosomes in liveborn neonates weighing less than 1000 g.

Cytogenetic investigations were performed in 37 phenotypically normal, liveborn immature neonates. Their mean birth weight was 758 g (range, 490-980 g), the mean gestational age was 24.2 weeks (range, 20-28 weeks). All the infants had normal karyotypes, no conspicuous structural aberrations and variants were found. It is presumed that while pregnancies with chromosomally abnormal zygotes are often terminated as fetal wastage or stillbirth, the phenotypically normal liveborn babies born even at a very early gestational age are likely to have normal chromosomes.