P07.05: Uterine artery blood flow volume growth rate in uncomplicated human pregnancies

Abstract

Objective: 1) To study uterine artery (UtA) flow (ml/min) growth rate along gestation in normal human pregnancies; 2) to evaluate longitudinal changes of UtA flow expressed per unit estimated fetal weight (EFW) (ml/min/kg). Methods: A cohort of twelve singleton uneventful human pregnancies, with a normal mean UtA PI, was included in this longitudinal study. UtA was evidenced by power-Doppler mode and sampled 10–15 mm prior to bifurcation. UtA diameter was measured on a perpendicular view after removing power-Doppler. UtA PI and velocity were measured with a Doppler beam angle < 30◦. The average of three consecutive diameters and velocities was considered. UtA flow was estimated by the formula Q = hV · πD2/4; h coefficient (0.5) was obtained by an ad hoc mathematical model. UtA total flow (ml/min) (right plus left UtA flow) was then expressed per EFW (ml/min/kg). Using linear interpolation, including random effects for the intercept and the slope of gestational age for each fetus, a linear mixed effects model was fitted. Results: Forty-seven ultrasound examinations were performed. Ultrasound exams were performed at 14.3,b1.2 weeks and every 4 weeks until delivery. Each case was definitively included in the study after recording normal perinatal and neonatal outcomes. UtA total flow (ml/min) showed a significant correlation to gestational age (133.6 ml/min at 15 weeks; 415.9 ml/min at 35 weeks) (p < 0.001), with a linear increase of 14.1 ml/min per week (right UtA 5.4 vs. left UtA 8.7 ml/min per week, p NS). UtA flow per unit EFW (ml/min/kg) showed a significant reduction from 780.3 ml/min/kg at 15 weeks to 144.1 ml/min/kg at 35 weeks (reduction rate 40.3 ml/min/kg per week). Conclusions: UtA flow (ml/min) significantly increased along gestation in this longitudinal cohort of normal pregnancies. UtA flow per unit EFW (ml/min/kg) significantly decreased longitudinally, since UtA flow (ml/min) growth rate was lower than fetal weight gain rate along gestation.