Chromosome findings in 2,500 second trimester amniocenteses.
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%.
D000649:Amniocentesis; D002869:Chromosome Aberrations / Q000453:epidemiology*; D025063:Chromosome Disorders; D002902:Chromosomes, Human, 16-18; D004314:Down Syndrome / Q000453:epidemiology; D005260:Female; D005820:Genetic Testing; D006801:Humans; D008423:Maternal Age; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis; D012729:Sex Chromosome Aberrations; D014178:Translocation, Genetic; D014314:Trisomy