Prenatal diagnosis and fetal therapy.

The protective effect of folic acid supplementation has been demonstrated in patients at risk of neural tube defects by a large, randomized double-blind study. The feasibility of second-trimester screening for Down syndrome, based on the combination of maternal and biochemical markers on maternal blood, has also been verified in two large series from both the United Kingdom and the United States. These results represent major advances in the field of prenatal diagnosis, which, in the future, is likely to rely more and more on better selection by noninvasive testing of high-risk patients. The emphasis has moved away from very early invasive testing due to concerns related to the safety of both early chorionic villus sampling and amniocentesis. Evaluation of renal damage in fetuses with obstructive uropathy by analysis of urinary biochemistry may constitute the basis for more efficient selection of cases amenable to antenatal treatment. Twin-to-twin transfusion syndrome remains a challenge for the future.