The role of midtrimester targeted fetal organ screening combined with the "triple test" and maternal age in the diagnosis of trisomy 21: a retrospective study.

OBJECTIVE: Our purpose was to evaluate the role of fetal ultrasonography in prenatal detection of trisomy 21. STUDY DESIGN: A retrospective study was performed on all cases of trisomy 21 diagnosed prenatally or postnatally between January 1990 and December 1993 in the Jerusalem metropolitan area. Our program of prenatal detection of trisomy 21 is a three-tiered, chronologically progressive screening that includes maternal age, biochemical serum markers, and targeted fetal organ survey. Sixty-seven thousand ninety-two babies were born during the study period; 17,084 maternal biochemistry analyses (triple test) were performed; and 6315 fetuses were karyotyped. RESULTS: One hundred eight cases of trisomy 21 were diagnosed prenatally and postnatally. The overall rate of detection of trisomy 21 was 92.2% when our recommendations were followed. Among those cases diagnosed prenatally, 66.6% of trisomy 21 cases had been referred for fetal karyotyping because of maternal age > or = 35 years, 18.5% because of abnormal triple test results, and 11.1% because of fetal ultrasonographic findings associated with trisomy 21. Among women < 35 years old, 80% of trisomy 21 cases were detected prenatally. Of these, 50% had been referred for karyotyping because of triple test results and 30% because of abnormal ultrasonographic findings. CONCLUSION: Midtrimester ultrasonographic targeted fetal organ screening plays a critical role in prenatal diagnosis of trisomy 21 among women under the age of 35 years.