BLOOD-VOLUME EXPANSION, PREECLAMPSIA, AND INFANT BIRTH-WEIGHT AT HIGH-ALTITUDE

Low blood volume (BV) during pregnancy is associated with intrauterine growth retardation and preeclampsia, which are more common at high al titude (HA) than at low altitude. We hypothesized that reduced BV expa nsion during pregnancy predisposed some women to develop preeclampsia and/or have lower-birth-weight infants at HA. BV was lower in 34 HA re sidents (3,100 m) than in 22 moderate-altitude residents (1,600 m) whi le non-pregnant (58.3 +/- 1.2 vs. 72.3 +/- 1.3 ml/kg; P < 0.001) and 3 6 wk pregnant (69.9 +/- 1.9 vs. 83.3 +/- 3.6 ml/kg; P < 0.01). BV fell between weeks 24 and 36 of pregnancy, and total BV increment with pre gnancy was less in women who developed preeclampsia or transient hyper tension at HA (n = 12). At HA, total blood and plasma volume expansion and arterial 0, saturation correlated negatively with the highest mea n arterial pressure recorded during pregnancy (r = -0.73, P < 0.01 and r = -0.58, P < 0.01, respectively). Total BV and late pregnancy chang e in BV correlated positively with infant birth weight. We concluded t hat BV expansion in normotensive pregnancy at HA vs. moderate altitude was similar but that nonpregnant BV was less among HA women, accounti ng for the low BV in pregnancy. HA women who developed preeclampsia or transient hypertension had less BV expansion, particularly during the third trimester, which was associated with smaller infants.