Chromosome variation in perinatal mortality: a survey of 500 cases.

The results of chromosome analyses on 500 cases of perinatal deaths are reported. It was found that 4.8% were chromosomally abnormal, but 90% of the chromosomally abnormal were either clinically malformed or macerated fetuses. Of the macerated fetuses, 9% were chromosomally abnormal and of these 33% had trisomy 21. The data suggest that the high loss of trisomy 21 fetuses in later stages of pregnancy is of an order sufficient to explain the discrepancy between the higher numbers of trisomy 21 detected during amniotic fluid sampling than found at birth in women of 35 years and over.