Objective: To determine uterine artery impedance using Doppler in the second and third trimesters at sea level and at high altitude.
Methods: Uterine artery resistance and pulsatility indices (RI and PI, respectively) were obtained by Doppler velocimetry from 242 women in Cerro de Pasco (4300 m altitude) and 200 women in Lima (sea level), all with normal singleton pregnancies between 14 and 40 weeks of gestation. Impedance indices at high altitude and sea level were compared using fractional polynomial regression analysis.
Results: Impedance to uterine artery blood flow was lower at high altitude than at sea level (for PI ratio Lima/Cerro de Pasco = 1.06; P = 0.011). If gestation bands were compared, the difference was significant up to 25 weeks.
Conclusion: At high altitude, pregnancy is associated with lower uteroplacental impedance than at sea level. This may reflect a compensatory mechanism of uteroplacental development to lower oxygen tension associated with altitude.