Midtrimester amniocentesis

Maternal, fetal, and neonatal results and complications were analyzed after 923 genetic amniocenteses. Maternal age of 35 years and beyond was associated with a 2.0% risk of fetal trisomy 21 and a 3.0% risk of all major chromosome abnormalities. Comparable rates for women aged 40 and beyond were 4.8% and 7.2%. Neural tube defects were detected in 0.15% of procedures done for maternal age and 3.4% of those done for a previous involved child. The risk of spontaneous abortion as a result of amniocentesis was 0.2% to 1.4%. Mahogany or green fluid was associated with a 29% rate of fetal loss. Unexplained midtrimester elevations of maternal serum α-fetoprotein were associated with a 38% risk of a subsequent low-birth weight infant. The only neonatal complication associated with amniocentesis was an apparent marked increase in the incidence of lower-extremity orthopedic abnormalities.