Abstract: Objective To explore the clinical value of screening the serum markers during the second trimester of pregnancy in
preventing congenital birth defect and predicting the pregnancy outcome. Methods Between November, 2011 and October,
2013, a total of 25 520 pregnant women (15-20 + 6 gestational weeks) underwent a screening test of triple serum markers
including free beta-human chorionic gonadotrophin (free β-hCG), alpha-fetoprotein (AFP), and unconjugated estriol (μE3)
during the second semester of pregnancy. The women identified by the screening test to have high risks were referred to
invasive prenatal diagnosis by amniocentesis, or to color Doppler ultrasound examination for suspected patent neural tube
defect (NTD), and their pregnancy outcomes were followed up. Results High-risk pregnancies were identified by the
screening test in 4.91% (1254/25520) of the total cohort. Of the 818 patients receiving invasive prenatal diagnosis, the abnormal
rate was 5.75% (47/818). The high-risk pregnancies identified by the screening test was associated with a significantly higher
rate of abnormal outcomes compared with the low-risk pregnancies (1.91% vs 0.1%, P<0.01). Of the 210 high-risk cases of NTD,
a definite diagnosis was established in 34 cases. We also found that pregnancies at an advanced age (>35 years) was associated
with increased risks for trisomy 21 compared with those at younger ages (15% vs 1.65% , P<0.01). The detection rate of
abnormal karyotypes in pregnancies with an abnormal MoM value of a single marker was 3.17% (6/189). Conclusion
Screening tests of serum markers during the second trimester of pregnancy can be helpful in identifying fetal chromosomal
and anatomical anomalies, predicting unfavorable pregnancy outcomes, and preventing birth defects in pregnancies at an
advanced age. The MoM value of a single marker in the second trimester can be indicative of potential chromosomal
abnormalities.