First and early second trimester diagnosis of anomalies of the central nervous system.

To study central nervous system development, 18 normally developing embryos or fetuses were examined sonographically between 6 and 16 weeks of pregnancy. Furthermore, in a 5 year period, 693 fetuses with an elevated risk for congenital defects were examined before 16 weeks of gestation. Abnormal development of the central nervous system was found in 28 fetuses. Early in pregnancy, normal central nervous system formation can be recognized, and pathologic cerebral development can be diagnosed already in the first trimester of pregnancy. We recommend routine use of safe and noninvasive transvaginal ultrasonography early in pregnancy for patients at risk.