[Strategies for selection of pregnancies with increased risk of fetal trisomy 21].

The main indications for cytogenetic prenatal diagnosis have been based on pregnancies with an increased risk of chromosomal anomaly. Advanced maternal age has been the most important criterion and presently 60% of women of 38 yr and over undergo prenatal diagnosis. Fetal malformations detected by ultrasound resulted in the selection of a group in which approximately 10% chromosomal anomalies were detected. An effort has been made to describe sonographic signs indicative of Down's syndrome. Maternal serum biochemical markers constitute another approach for screening. Human chorionic gonadotropin is the most discriminant test. Combining maternal and hCG cut-off levels, it is possible to detect approximately 70% of trisomy 21% in women aged between 30-38 yr.