Fetal Heart Rate at 12 Weeks' Gestation and the Risk of Preterm Birth

OBJECTIVES: To prospectively validate the association between fetal heart rate (FHR) at the 12-week scan and the risk of preterm birth (PTB), including spontaneous preterm birth (sPTB). METHODS: This prospective cohort study included 1276 singleton pregnancies undergoing routine first-trimester screening at 11-13 + 6 weeks' gestation and followed until delivery. Associations between FHR and PTB outcomes were assessed using univariable and multivariable logistic regression analyses and receiver operating characteristic (ROC) curves, incorporating clinical, sonographic, and biochemical first-trimester parameters. RESULTS: Compared with term births, pregnancies resulting in PTB (n = 34) and sPTB (n = 23) showed significantly higher FHR at the 12-week scan (163.6 versus 160.1 bpm, p = .007; and 164.1 versus 160.1 bpm, p = .014, respectively). In univariable analyses, FHR was the only parameter consistently associated with PTB, PTB <34 weeks, sPTB, and sPTB <34 weeks (odds ratios per bpm increase ranging from 1.08 to 1.12). Free β-human chorionic gonadotropin (free-βhCG) was associated with PTB <34 weeks and showed borderline significance for other PTB outcomes. In multivariable models, FHR showed the highest predictive performance for sPTB <34 weeks (AUC 0.73; detection rate 25% at a 10% false-positive rate), which improved when combined with free-βhCG (AUC 0.81; detection rate 43% at a 10% false-positive rate). CONCLUSION: Elevated FHR at the 12-week scan is associated with sPTB, particularly before 34 weeks' gestation. FHR, especially when combined with free-βhCG, may contribute to early first-trimester screening strategies for sPTB.