False positive serum biochemical screening and subsequent fetal loss in women less than 35 years of age.

Abstract

To examine the fetal loss rate in women younger than 35 years of age following a false positive serum biochemical screening. Retrospective analysis of case records between 1991 and 1998. Fetal medicine unit of a large teaching hospital. Four hundred and fifty-six women with singleton pregnancies and false positive serum biochemical screening for Down's Syndrome (study group). Nine hundred and twelve matched controls with true negative serum biochemical screening (control group). Women of both groups had a second trimester serum screening for Down's Syndrome using alpha fetoprotein, human chorionic gonadotrophin (hCG) and unconjugated oestriol (uE3); and they also underwent genetic amniocentesis. The overall fetal loss rate in the study group was 5.3% (24/456), compared with 1.65% (15/912) in the control group RR 3.2, 95% CI 1.7-5.99; P < 0.001). The majority of fetal losses in the study group occurred after 28 weeks, while in the controls this happened between 24 and 28 weeks of gestation. A false positive serum biochemical screening in women under 35 years of age is associated with a threefold increased risk of subsequent fetal loss. However, most of fetal losses in this group occurred after 28 weeks, indicating that intensive antepartum fetal surveillance could improve the perinatal outcome.