EFFECT OF ALTITUDE ON UTERINE ARTERY BLOOD-FLOW DURING NORMAL-PREGNANCY

To determine whether uterine blood flow was reduced and indexes of pel vic blood flow distribution altered in normotensive pregnancy at high (3,100 m) compared with low altitude (1,600 m), we measured uterine, c ommon iliac, and external iliac artery blood flow velocities and diame ters in women during pregnancy and again postpartum. Pregnancy increas ed uterine artery diameter, blood flow velocity, and volumetric flow a t both altitudes. Uterine artery blood flow velocity was greater (69.0 +/- 2.2 vs. 59.4 +/- 3.0 cm/s; P < 0.005) but diameter was smaller at 3,100 m than at 1,600 m (2.5 +/- 0.3 mm vs. 3.4 +/- 0.2 mm; P < 0.005 ), resulting in volumetric flow that was one-third lower at week 36 of pregnancy (203 +/- 48 vs. 312 +/- 22 ml/min, respectively; P < 0.01). Pregnancy increased common iliac blood flow velocity and decreased ex ternal iliac artery blood flow velocity at both altitudes. The uterine artery received a smaller percent of common iliac flow at 3,100 than at 1,600 m (46 +/- 7 vs. 74 +/- 6%; P < 0.005). Gestational age was si milar but birth weight was lower at 3,100 m than at 1,600 m. Among sub jects at 1,600 m, variation in uterine blood flow velocity correlated positively with infant birth weight. We concluded that reduced uterine blood flow and altered pelvic blood flow distribution during pregnanc y at high altitude likely contributed to the altitude-associated reduc tion in infant birth weight.