Role of Second-Trimester Uterine Artery Doppler in Assessing Stillbirth Risk

OBJECTIVE: To estimate the association between uterine artery Doppler indices and stillbirth in routinely screened populations. METHODS: Second-trimester uterine artery Doppler indices at 19 to 23 weeks of gestation were obtained from a large cohort of women. Pregnancy losses recorded on a mandatory national register were cross-linked to the Doppler database. Kaplan-Meier curves were constructed for the risk of stillbirth based on the uterine artery Doppler resistance indices. Logistic regression analysis was used to assess the influence of uterine artery Doppler indices and other more conventional risk factors on the likelihood of stillbirth. RESULTS: Data were available from 15,835 women with 144 stillbirths (9.1 stillbirths per 1,000 births). Kaplan-Meier analysis showed that the risk of stillbirth (39.41 per 1000) in women with uterine artery Doppler indices greater than the 90th percentile was sevenfold higher (95% confidence interval 4.81-9.57) than the reference population (5.36 per 1000) with Doppler indices less than or equal to the 90th percentile. The positive predictive and negative predictive values for the 90th percentile uterine artery Doppler cut-off were 0.46% and 95.73%, respectively. The sensitivities of the 90th, 95th, and 99th percentile uterine artery Doppler resistance index cutoffs for the sensitivity of stillbirth were 46.2%, 35.4%, and 15.4%, respectively. Conventional risk factors for term stillbirth such as ethnicity, body mass index (BMI), and smoking no longer contributed to stillbirth risk when uterine artery Doppler indices were included in multivariable logistic regression analysis. CONCLUSION: Elevated second-trimester Doppler indices, a proxy for impaired placentation, are more strongly associated with stillbirth than conventional risk factors. Risk factors such as ethnicity, maternal age, BMI, and smoking contribute to risk of term stillbirth through uteroplacental dysfunction.