Uterine artery blood flow during pregnancy in high-altitude aymara women

Abstract

Background. Birth weight falls with increasing altitude as the result of intrauterine growth restriction (IUGR) likely due, in turn, to lower uterine artery (UtA) blood flow. The altitude-associated birth weight decline is least in the longest resident (in generations) groups, suggesting that adaptations may have occurred that raise uteroplacental blood flow to near sea-level values (Moore et al. HAMB 2001). Study Objective: Determine the factors responsible for raising UtA blood flow in Andean pregnant women, and whether the values near term resemble those of low-altitude residents. Methods: Measurements of the vessel diameters and blood flow velocities (averaged throughout the cardiac cycle) were made for the UtA, common iliac (CI), and external iliac (EI) arteries at 20, 30, and 36 weeks of pregnancy and 3 months postpartumto measure the nonpregnant state, using Doppler ultrasound (ATL 3000 and an investigational Doppler Velocimeter). Results: UtA volumetric flow increased as a result of an early enlargement of UtA diameter with a continued, progressive rise in flow velocity. There was a corresponding rise in CI flow, which was increasingly directed to the UtA (see figure). The increase in CI flow was due primarilyto an increase in vessel diameter. The near term UtA volumetric flow appears similar to that of low-altitude residents (wk 36 value = 353 mL/min, Palmer Ob Gyn 1992), consistent with our hypothesis. This suggests that selection may have acted on the factors responsible for raising UtA diameter and flow velocity. (HL60131, TW01188)