Relationship between second-trimester uterine artery Doppler and spontaneous early preterm delivery.

OBJECTIVE To evaluate the relationship between impedance to flow in the uterine arteries at 22-24 weeks and subsequent spontaneous delivery before 33 weeks. METHODS The pulsatility index (PI) in the uterine arteries was measured by transvaginal sonography at 22-24 weeks in 33,629 women with singleton pregnancies attending for routine antenatal care. The distribution of PI in the 237 patients with live births before 33 weeks, after spontaneous onset of labor, was compared to that in 31,633 patients with live births at or after 33 weeks. RESULTS The median uterine artery mean PI was significantly higher in those women delivering before 33 weeks than in those delivering at or after 33 weeks. The mean PI was 1.57, which is the 95th centile, in 1525 (4.8%) of those delivering at or after 33 weeks and in 19 (8.0%) of the deliveries before 33 weeks. Multiple regression analysis demonstrated that the significant predictors of spontaneous delivery before 33 weeks were ethnic origin, smoking status, previous obstetric history and uterine artery mean PI. However, the prediction of spontaneous early preterm delivery by a combination of maternal characteristics and uterine artery Doppler was not significantly higher than maternal characteristics alone (area under the receiver-operating characteristics curve: 0.704, 95% CI 0.669-0.740 vs. 0.684, 95% CI 0.647-0.722; P = 0.062). CONCLUSIONS Uterine artery PI in spontaneous deliveries before 33 weeks is higher than in those women delivering at or after 33 weeks. However, uterine artery Doppler does not provide a significant improvement in the prediction of spontaneous early delivery provided by maternal demographic characteristics and previous obstetric history.