Objective: To determine whether a false-positive second trimester serum screen for Down syndrome in Thai pregnant women is predictive of adverse pregnancy outcomes.
Material and Method: The relationship between adverse pregnancy outcomes in women and a false-positive screening for Down syndrome was investigated in a case-control study. The Double-marker maternal serum screening for Down syndrome (alpha-fetoprotein and free β-hCG) was performed on Thai pregnant women between 14 and 21 weeks’ gestation at Charoenkrung Pracharuk Hospital from March 1998 to August 2002. The pregnancy outcomes of 165 women having false positive serum screening (risk ratio at least 1:270; study group) were compared to the outcomes of 165 control patients having negative serum screening results (control group). The outcome indices analyzed were preterm delivery, low birth weight newborn, small-forgestational age newborn, preeclampsia, placenta previa, and fetal death.
Results: The incidence of adverse pregnancy outcomes was 18.2% in the study group and 15.2% in the control group (odds ratio = 1.244; 95% confidence interval = 0.696, 2.225; p = 0.46). Women in the study group delivered at a significantly lower birth weight of newborns than women in the control group did (3088.1 + 543.9 versus 3229.1 + 454.6 g, respectively; p = 0.011). No significant differences in adverse outcomes was discovered after the comparisons between the study group and the control group: preterm delivery 11 of 165 (6.6%) versus 5 of 165 (3%), p = 0.124; low birth weight newborn 11 of 165 (6.6%) versus 6 of 165 (3.6%), p = 0.213; small for gestational age newborn 4 of 165 (2.4%) versus 0 of 165 (0%), p = 0.123; preeclampsia 16 of 165 (9.7%) versus 12 of 165 (7.3%), p = 0.429; placenta previa 4 of 165 (2.4%) versus 4 of 165 (2.4%), p = 1; fetal death 1 of 165 (0.6%) versus 0 of 165 (0%), p = 1.
Conclusion: The present findings revealed no apparent increase in the adverse pregnancy outcomes analyzed in women with false positive Down syndrome screening test.

Keywords: False-positive Down syndrome screening test, Adverse pregnancy outcomes