Strategies for antenatal detection of Down's syndrome.

AIM To predict the effect of maternal serum screening and fetal echocardiography on the birth prevalence of Down's syndrome. METHODS The outcome of all Down's syndrome pregnancies in the Northern Health Region between 1985 and 1991 was retrospectively ascertained. The number and outcome of all Down's syndrome pregnancies were used to define a theoretical population which would exist in the absence of screening. Published reports were used to predict the effects of screening strategies. RESULTS Down's syndrome was identified in 412 pregnancies of which 315 (76%) resulted in live birth. A theoretical population with no antenatal screening would be expected to produce 31 stillbirths and 381 (92%) live births affected by Down's syndrome. In the same population a programme of maternal serum screening and fetal echocardiography would lead to 155 and 14 terminations, respectively, and when combined, would reduce affected live births to 229 (56%). CONCLUSIONS Even if maternal serum screening and fetal echocardiography achieve their predicted potential, around half of all pregnancies affected by Down's syndrome will result in live born babies.