Amniocentesis is generally performed at 105 to 125 days post last menstrual period (LMP) and TA CVS at 63 to 76 days post LMP. This study will compare the safety and accuracy of transabdominal amniocentesis and TA CVS, each performed during the same modified gestational age window of 77 to 104 days post LMP.

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 a baseline ultrasound. Eligible women who refuse randomization or for whom a procedure cannot be scheduled by 104 days will also be followed. Primary outcomes include fetal loss or preterm delivery before 196 days gestation as well as 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. One ancillary study will evaluate the feasibility and accuracy of fluorescence in situ hybridization (FISH) as a rapid diagnostic method for certain cytogenetic abnormalities; another will collect data on amniotic fluid alphafetoprotein and acetylcholinesterase for the diagnosis of neural tube defects.