Effect of normal and preeclamptic pregnancies on the oxyhemoglobin dissociation curve.

Hemoglobin affinity for oxygen in whole blood of ten normal nonpregnant women, ten normal pregnant women at first trimester, ten normal pregnant women at second trimester, 24 normal pregnant women at or near term, and 14 pregnant women with preeclampsia at or near term was studied. The mean P-50 values for normal nonpregnant women, normal pregnant women in first trimester, second trimester, and at or near term were 26.7 +/- 0.11 mmHg, 27.8 +/- 0.08 mmHg, 28.8 +/- 0.17 mmHg, and 30.4 +/- 0.20 mmHg, respectively. The mean P-50 of pregnant women with preeclampsia at or near term was 25.1 +/- 0.38 mmHg. It is concluded that in normal pregnant women there was a significant shift of P-50 to the right compared with the normal nonpregnant women (P less than 0.01), and the extent of this shift to the right is directly related to the duration of the pregnancy. In addition, preeclamptic parturients showed a significant shift of P-50 to the left when compared with normal pregnant women at or near term (P less than 0.001).