Amniocentesis for chromosome analysis was performed in 1086 pergnant women, 739 of whom had an increased risk of giving birth to a child with chromosome abnormalities. Such abnormalities were found in almost identical proportions among the fetuses with an increased risk (1.2%) and among those with no increased risk (1.4%). Findings in several other studies seem to confirm that there is no significant difference between the risk groups in the proportion of abnormalities found. This suggests that our current risk groups may not be the right ones, but a much larger study is needed to confirm this.