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Keywords:

  • amniocenteses;
  • prenatal diagnosis;
  • trisomy 21;
  • sex chromosome abnormality;
  • trisomy 18;
  • translocation;
  • mosaicism;
  • neural tube defect

Abstract

We have analyzed the chromosome abnormalities found in 2,500 amniocenteses for prenatal diagnosis; 1,887 (75%) were performed because the maternal age was 34 years or more. Chromosome abnormalities were detected in 1.80% of those referred for advanced maternal age, 1.2% between ages 34 and 39 years and 4.6% 40 years and over. Of these, four occurred in women who would have been 34 years at delivery (2.9%). Trisomy 21 accounted for 50% of the chromosome abnormalities; sex chromosome abnormalities, for 25%; the remaining 25% was divided equally between trisomy 18 and partial trisomies and mosaics. Unexpected translocations were found in 0.4%, of which two-thirds were balanced and identified in one parent. The accuracy was 99.6%.