May high oxygen affinity of maternal hemoglobin cause fetal growth retardation?

Eleven pregnant women with normal fetal outcome (controls), seven women with small for dates babies and 15 non-pregnant women were studied. Hemoglobin (Hb), hematocrit (Hct) and the half saturation tension of oxygen, P50-value (as a measure for the oxygen affinity of Hb) were measured. Urine estriol excretion, HPL in plasma and antepartum cardiotocograms served as parameters of fetal well-being. The placental weight and the largest placental diameter were measured immediately after birth. The patients with small for dates babies showed significant lower P50-values (27.3 +/- 0.4 mm Hg) than those without growth retardation (28.5 +/- 0.3 mm Hg) and were in the range of the non-pregnant controls (27.4 +/- 0.2 mm Hg). Hb was 135.2 +/- 3.8 g/l in the patients with small for dates babies, 118.3 +/- 4.3 g/l in pregnant controls and 136.8 +/- 3.3 g/l in non-pregnant women. Hematocrit paralleled the Hb. The placental weights were significantly lower in women with small for dates babies, but no difference in placental diameters was found. These data, higher oxygen affinity of Hb, increased Hct and lower placental weight, indicate an unfavourable situation in regards to placental oxygen transfer with possible chronic hypoxia of the fetus.