Little effect of gestation at 3,100 m on fetal fat accretion or the fetal circulation

While chronic hypoxia has been recognized as the principal causative factor for decreasing birth weight at high altitude, unknown is whether fetal fat accretion and vascular function are affected.

Colorado women with normal singleton pregnancies (18 Denver residents, 1,600 m; 24 Leadville residents, 3,100 m) were studied longitudinally from 20 to 36 weeks gestation. Fetal biometry was used to obtain axial images for assessing mid-upper arm and mid-thigh subcutaneous tissue mass (MUA and MUL SQ) and Doppler waveform analysis conducted to measure indices of vascular function in the fetal umbilical arteries (UmbA), umbilical vein (UmbV), middle cerebral artery (MCA), and ductus venosus (DV). SAS PROC MIXED was used to compare altitudes with P < 0.05 considered significant and trends present when 0.05 < P < 0.10.

The 3,100 m vs. 1,600 m babies weighed less at birth. Third trimester fetal biometry, MUA SQ and MUL SQ were somewhat lower, but neither the biometry nor the SQ altitudinal differences attained statistical significance. Greater prepregnant maternal BMI tended to decrease MUA SQ (P = 0.07) and increase MUL SQ (P = 0.07). UmbA S/D ratios decreased and UmbV flow increased with advancing gestation (both P < 0.001). Altitude did not affect the UmbA or MCA systolic/diastolic ratios (S/D), MCA peak-systolic velocity, UmbV flow, or the DV systolic/atrial flow ratio.

The hypoxia of residence at high compared to moderate altitude lowered birth weight but did not significantly alter MUA or mid-thigh fetal subcutaneous tissue mass or Doppler indices of vascular function.