DESCRIPTION: This is a revised proposal for a randomized comparison of the safety and accuracy of transabdominal amniocentesis and transabdominal CVS, each done during the same modified gestational age window of 77-104 days post last menstrual period (LMP) in contrast to 105-125 days post LMP for amniocentesis and 63-76 days post LMP for CVS. A consortium of 12 experienced prenatal diagnostic centers has been formed to facilitate patient acquisition and completion of the proposed project in a timely fashion. The group includes as principal investigators researchers with expertise in obstetrics, medical genetics, cytogenetics, pediatrics, epidemiology, biostatistics, and the conduct of cooperative clinical trials. The specific aims for the study are to compare transabdominal amniocentesis and CVS at 77-104 days gestation with respect to: Preterm delivery or fetal loss from cytogenetically normal pregnancies, at less than 28 completed gestational weeks; total fetal loss including neonatal death before discharge; Amniotic fluid loss resulting in a pocket of less than 1 cm; gestational age at delivery; perinatal morbidity: intrauterine growth retardation (IUGR), neonatal respiratory problems and other complications; limb defects and other congenital anomalies of the newborn; failure to obtain a sample for diagnosis; failure to obtain a diagnosis; cytogenetic accuracy for diagnosis of abnormal karyotype (by standard culture methods); the diagnostic accuracy and applicability of fluorescence in situ hybridization (FISH) in CVS and amniotic fluid samples, as compared with standard methods; the accuracy of amniotic fluid alphafetoprotein and acetylcholinesterase at 77-104 days gestation for diagnosis of neural tube defects.