his study is a multicenter randomized clinical trial of amniocentesis and transabdominal chorionic villus sampling (TA CVS) at 77-104 days gestation. The Biostatistics Center serves as the Data Coordinating Center for the study. The purpose of this study is to compare the two prenatal diagnosis techniques with regard to safety, measured primarily by a combined endpoint of fetal loss or preterm delivery before 196 days gestation and also by total fetal loss, amniotic fluid loss, gestational age at delivery, perinatal morbidity, neonatal morbidity and congenital abnormalities, including limb reduction defects. Success in obtaining a diagnosis from the two procedures will be compared. A total of 6400 healthy pregnant women at 77 to 104 days gestation, whose only indication for prenatal diagnosis is advanced maternal age of at least 34 years at enrollment, will be randomized to receive either TA CVS or amniocentesis following the baseline ultrasound. Eligibility criteria were revised in 1998 to restrict participation to women at 91-104 days gestation.

n 1998 investigators initiated the First Trimester Maternal Serum Biochemistry and Fetal Nuchal Translucency Screening Study (BUN). The purpose is to assess in the U.S. a system for 1st trimester screening which uses combined serum biochemistry and ultrasound measurement of nuchal translucency together with maternal age and gestational age to calculate the risk of Down Syndrome and Trisomy 18. BUN is a prospective observational study of approximately 60,000 women to test the sensitivity and specificity of this screen for genetic abnormality. Supported by appropriate counseling any risk positive mother choosing an invasive diagnostic procedure is asked for consent to randomize into the EATA Trial. Grant funded by NICHD, 1-R01-HD32109-01A1, 1996-2000.