The effect of gestational age and placental location on the prediction of pre-eclampsia by uterine artery Doppler velocimetry in low-risk nulliparous women.

OBJECTIVE: To assess how placental position and gestational age can influence the value of a diastolic notch of the uterine arteries as a screening test for pre-eclampsia, in a low-risk population of healthy nulliparous women.
METHODS: Color Doppler ultrasound was used to examine both uterine arteries in 654 healthy nulliparas at 4-week intervals between 20 and 32 weeks. The only criterion for an abnormal result was the presence of an early diastolic notch. In each subject the placental position was also recorded. The major end points were pre-eclampsia and pre-eclampsia requiring delivery before the 34th week.
RESULTS: Ninety-eight women (15%) had abnormal flow velocity waveforms at their first visit. Twenty-one out of 654 women developed pre-eclampsia (3.2%). The sensitivity of the test became lower as gestational age advanced and ranged from 81% at 20 weeks, to 71.4% at 32 weeks. In contrast, the specificity and positive predictive value increased significantly. Eleven out of 12 women who delivered before 34 weeks had abnormal waveforms at the 24th week. In women with a full lateral placenta, the predictive value of the test was extremely low, especially in cases with unilateral notches.
CONCLUSION: Pre-eclampsia can be more accurately predicted if, along with the presence of a notch, both gestational age and placental position are taken into account. At week 24 the test maintains a high sensitivity (76.1%), but also has an improved specificity (95.1%) and positive predictive value (34%), which allow the clinician to intervene with a potential preventive treatment.