Reduction of subcutaneous mass, but not lean mass, in normal fetuses in Denver, Colorado

OBJECTIVE: To test the hypothesis that reduced birth weight in normal fetus es born at moderately high altitude (Denver), compared with the birth weigh t in normal fetuses born at sea level (Milan), Is caused by a reduction in both lean mass and subcutaneous fat mass. STUDY DESIGN: Ninety-four normal singleton pregnancies (46 in Deriver, 48 i n Milan) had serial ultrasonographic axial images obtained to assess subcut aneous tissues of fetuses as a measure of body fat. The abdominal wall thic kness and mid upper arm and mid thigh were examined. The equation was: Subc utaneous tissue equals total cross-sectional area minus bone and muscle are a. Lean mass included the area of muscle and bone, head circumference, and femur length. RESULTS: Gestational age at delivery was similar between groups. Birth weig ht was less at Denver's altitude (2991 +/- 79 g versus 3247 +/- 96 g; P =.0 4). Abdominal wall thickness, mid upper arm, and mid thigh subcutaneous tis sues measurements were significantly reduced at Denver's altitude and incre ased further in significance with advancing gestational age. Lean mass meas urements were similar between groups. CONCLUSIONS: The reduced birth weight of the newborns in Denver was the res ult of a reduction in fetal subcutaneous fat tissue and not lean mass. Ultr asonography can be used to follow subcutaneous measurements longitudinally and to detect differences, and potentially disease processes, In study popu lations.