Ultrasonographic features of uterine blood flow during the first 16 weeks of pregnancy.

Abstract

Uterine blood flow volume has been thought to increase in a linear fashion throughout pregnancy, but previous studies in early pregnancy may have not been performed often enough or in sufficient numbers of patients. We measured uterine artery blood flow volume, average velocity, vessel cross-sectional area, resistance index, and spiral artery resistance index with Doppler ultrasound at 1-3 week intervals from gestational (post-menstrual) weeks 5-6 to week 16 in 44 normal, spontaneous, single pregnancies. Uterine artery blood flow volume and velocity increased gradually until the end of week 9, and then rapidly from weeks 10-16. Uterine artery vessel size increased linearly. The uterine artery resistance index was the inverse of volume and velocity, in contrast to the spiral artery resistance index, which decreased linearly. These findings indicate that early pregnancy changes in uterine and spiral artery blood flow occur by different mechanisms, and that when investigating uterine blood flow in early pregnancy, studies need to begin by week 6 and need to be performed at least biweekly.