Risk of amniocentesis in women screened positive for Down syndrome with second trimester maternal serum markers.

In routine obstetrical practice, prior to offering invasive prenatal diagnosis, it is crucial to weigh the risks attendant on amniocentesis against the individual's risk of aneuploidy. We took advantage of a policy of follow-up of patients undergoing Down syndrome maternal serum screening to compare the rates of fetal loss before 24 weeks and of early premature delivery at 24-28 weeks between women who underwent amniocentesis and women who did not. A total of 54 902 patients entered the study, of whom 4039 (7.