[Antenatal screening for Down syndrome: a smattering of epidemiology]

Maternal age per se is not an indication for chorionic villous sampling or amniocentesis anymore. Although the risk for fetal Down syndrome increases with maternal age, it must be adjusted after other screening tests are performed. Current recommendations include ultrasound measurement of the fetal nuchal transluciency, and of maternal PAPP-A and free-b-hCG in addition to maternal age. This strategy has a sensitivity of 80 to 90%, with false positive rate of 5%. The thickness of fetal nuchal transluciency is strongly associated with the risk of Down syndrome, and measurement must be performed by an experie ced sonographer. For women with an intermediate risk (1/380 to 1/1000), a genetic son gram allows a reassessement of the risk and may help couples to make a decision of invasive sampling.