A randomized controlled trial of aspirin in patients with abnormal uterine artery blood flow

To evaluate color Doppler imaging of the uterine arteries as a screening test in nulliparous women, and to examine the role of low-dose aspirin therapy in pregnancies with abnormal uteroplacental resistance.

At the routine 18-week fetal morphology ultrasound scan, 955 nulliparous women underwent color Doppler imaging of the uterine arteries. Abnormal uteroplacental vascular resistance was defined with respect to both the systolic-diastolic ratio of the flow velocity waveform and the presence of an ipsilateral early diastolic notch. Those with abnormal uterine artery waveforms were asked to participate in a randomized controlled trial of aspirin therapy. Pregnancy outcomes were compared in women with normal or abnormal flow velocity waveforms, as well as in the two arms of the intervention study.

Of 186 women with abnormal uteroplacental resistance according to criteria defined previously, 102 agreed to randomization to either low-dose aspirin (100 mg/day) or placebo for the remainder of the pregnancy. Abnormal uterine artery flow velocity waveforms were associated with statistically significant increases in preeclampsia (11 versus 4%), birth weight below the tenth percentile (28 versus 11%), and adverse pregnancy outcome (45 versus 28%). Prophylactic aspirin therapy did not result in a significant reduction in pregnancy complications.

Abnormal uteroplacental resistance at 18 weeks' gestation was associated with a significant increase in adverse pregnancy outcome. Low-dose aspirin did not reduce pregnancy complications in women with uteroplacental insufficiency.