Trisomy 13 ascertained in a survey of spontaneous abortions.

In a series of 2922 karyotyped spontaneous abortions, 62 were found to be trisomic for chromosome 13, 46 having a simple trisomy and 16 a translocation trisomy. The epidemiology of this series of trisomy 13 conceptuses is presented and compared to that of trisomy 13 ascertained from other populations. In most compared parameters the trisomy 13 spontaneous abortions are very similar. However, there is no evidence in our material for the fall in proportion of trisomy 13 conceptuses at very advanced maternal ages that has been reported in three previous studies, one of spontaneous abortions and two of amniocentesis specimens.