Nunthapiwat S, et al. - The association between second-trimester serum Down syndrome screening (alpha-fetoprotein [AFP] free beta-human chorionic gonadotropin [b-hCG] unconjugated estriol [uE3]) and preterm birth was investigated and predictive models for preterm birth was created. A prospective database of pregnancies undergoing second-trimester screen was secondarily analyzed with complete follow-up. Of 20,780 pregnancies, 1,554 (7.5) had preterm births, 363 (1.7) had early preterm births, and 158 (0.8%) had very early preterm birth. They noted a significant association of high levels of AFP and b-hCG but low levels of uE3 with higher rates of preterm, early preterm and very early preterm delivery. In predicting preterm birth, the predictive models displayed diagnostic performance with the areas under the ROC curve of 0.688, 0.534, 0.599, and 0.718 for AFP, b-hCG, uE3, and combined biomarkers, respectively. Findings thereby suggest the additional utility of the second trimester Down syndrome screening as a tool of risk identification of preterm birth in the same test, without extra-effort and extra-cost.