Genetic sonography - An option for women of advanced maternal age with negative triple-marker maternal serum screening results

Objective. To determine whether offering genetic sonography to patients 35 years of age and older with negative maternal serum triple-marker screening results will result in an increase in the detection rate of trisomy 21. Methods. The detection rate of trisomy 21 was determined in women 35 years of age and older whose pregnancies were managed according to the following 3 policies: policy 1, universal amniocentesis; policy II, maternal serum triple-marker screening followed by amniocentesis only in high-risk women (risk >1:190),- and policy III, genetic sonography in women with negative maternal serum screening results (policy II). Policy III included the offering of genetic amniocentesis to patients with abnormal genetic sonographic findings. The rate of acceptance of genetic amniocentesis was modeled, as was the sensitivity (50%-90%) and false-positive rate (5%-25%) of genetic sonography. Results. The number of fetuses expected to have trisomy 21 was 784. For patients evaluated under policy II, 86.3% of fetuses with trisomy 21 were detected. On the basis of the detection rate for trisomy 21 of policy II, the addition of fetuses with trisomy 21 identified under policy III was significantly (P <.01) increased (93.2% to 98.6%) for genetic sonographic sensitivities ranging between 50% and 90%. Conclusions. A policy of offering genetic sonography followed by amniocentesis to patients 35 years of age and older who originally had triple-marker maternal serum screening findings that were negative for the diagnosis of trisomy 21 results in a higher overall detection rate of trisomy 21.