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

Uterine blood flow volume has been thought to increase in alinear fashion throughout pregnancy, but previous studies inearly pregnancy may have not been performed often enough orin sufficient numbers of patients. We measured uterine arteryblood flow volume, average velocity, vessel cross-sectionalarea, resistance index, and spiral artery resistance index withDoppler 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 velocityincreased gradually until the end of week 9, and then rapidlyfrom weeks 10–16. Uterine artery vessel size increasedlinearly. The uterine artery resistance index was the inverseof volume and velocity, in contrast to the spiral artery resistanceindex, which decreased linearly. These findings indicate thatearly pregnancy changes in uterine and spiral artery blood flowoccur by different mechanisms, and that when investigating uterineblood flow in early pregnancy, studies need to begin by week6 and need to be performed at least biweekly.