Association Between First-Trimester Serum PAPP-A and Free β-hCG Levels and Gestational Duration: A Retrospective Cohort Study

BACKGROUND: Gestational duration is influenced by multiple factors, with placental function being one of the key determinants. First-trimester serum biomarkers reflect the quality of placentation and may be associated with the duration of pregnancy. AIMS: To investigate the association between first-trimester serum placental biomarkers and gestational duration, and to evaluate the independent effects of nulliparity and fetal sex on gestational length. METHODS: This retrospective, single-center study included 346 singleton pregnancies delivered between 34 + 0 and 41 + 0 weeks of gestation following spontaneous labor. First-trimester PAPP-A and free β-hCG multiples of the median (MoM) values were measured. Gestational length was calculated as the interval between the estimated last menstrual period and the date of delivery. Spearman correlation analysis and multiple linear regression were used to assess associations with gestational duration. RESULTS: The mean gestational duration was 271 ± 10.5 days. Pregnancy duration was significantly longer in the PAPP-A MoM ≥ 0.6 group compared to the < 0.6 group (273 vs. 269 days, p = 0.001). In multiple linear regression analysis, PAPP-A MoM (B = 2.08, p = 0.034), nulliparity (B = 2.96, p = 0.013), and fetal sex (B = 2.63, p = 0.022) were identified as independent predictors of gestational duration. No significant association was observed between free β-hCG MoM and gestational duration. CONCLUSIONS: Higher first-trimester PAPP-A MoM levels are independently associated with longer gestational duration, even after adjustment for parity and fetal sex, suggesting that early placental function may play a role in regulating the timing of parturition with modest effect.