Effect of parity on second-trimester uterine artery Doppler flow velocity and waveforms

To investigate the relationship between second-trimester uterine artery Doppler findings and parity in a large pregnant population.

Uterine artery Doppler studies were performed in all singleton pregnancies at 18-23 weeks of gestation. The mean uterine artery resistance index and the presence or absence of protodiastolic notches were recorded. Two groups were identified: pregnancies not complicated by pre-eclampsia, and pregnancies with pre-eclampsia severe enough to require delivery at or before 32 weeks of gestation.

In the 4132 pregnancies uncomplicated by pre-eclampsia, parity was shown to be an independent predictor for both mean uterine artery resistance index (beta = 0.073, P < 0.001) and the presence of bilateral protodiastolic notches (odds ratio = 0.67; 95% CI, 0.45-0.98). In the 17 pregnancies complicated with severe pre-eclampsia, uterine artery Doppler indices showed a trend towards being better predictors of disease in nulliparous compared with parous women.

Parity has a significant effect on the resistance index and the prevalence of protodiastolic notching in the uterine artery flow waveforms. This difference is clinically noticeable in its effect on notching. These findings suggest that some permanent modification may persist in the maternal vessels after a successful pregnancy, altering their impedance in subsequent pregnancies.