Effect of maternal heme degradation on fetal carboxyhemoglobin concentration in pregnancy-induced hypertension

Abstract

Increased red cell destruction with consequent heme catabolism results in accumulation in carboxyhemoglobin in women with pregnancy-induced hypertension. Temporally associated with this is a significant shift in the oxyhemoglobin dissociation curve to the left. In this study we assessed the relationship between carboxyhemoglobin concentration and oxyhemoglobin dissociation curve in simultaneously obtained maternal and fetal venous blood in which patients with pregnancy-induced hypertension were compared with normotensive patients. Maternal and fetal carboxyhemoglobins were significantly higher in patients with pregnancy-induced hypertension than in control subjects. Fetal carboxyhemoglobin was significantly higher than maternal carboxyhemoglobin in both clinical groups. Furthermore, maternal and fetal oxyhemoglobin dissociation curves were significantly shifted to the left in patients with pregnancy-induced hypertension compared with controls. The fetal-maternal gradient of carboxyhemoglobin was similar in both groups. The maternal-fetal gradient of oxyhemoglobin dissociation curve position was significantly reduced in pregnancy-induced hypertension. The concentrations of carboxyhemoglobin measured do not fully explain the magnitude of the shift in oxyhemoglobin dissociation curve, but the data suggest a potential impact on fetal oxygenation in pregnancy-induced hypertension.