Fetal haemoglobin measurement in the assessment of red cell isoimmunisation.

A reference range of fetal haemoglobin concentration (g/dl) was established from umbilical cord blood samples obtained by cordocentesis (n = 200) or at delivery (n = 10). In normal pregnancy the mean fetal haemoglobin increases linearly from 11 g/dl at 17 weeks' gestation to 15 g/dl at 40 weeks' gestation and one standard deviation is approximately 1 g/dl. The haemoglobin was also measured in fetal blood from 154 red cell isoimmunised pregnancies from 17 to 36 weeks' gestation. In 48 fetuses with ultrasound features of hydrops the haemoglobin was 7-10 g/dl below the normal mean for gestation. It is proposed that in pregnancies complicated by red cell isoimmunisation the severity of the disease should be assessed and treated on the basis of the deviation of the fetal haemoglobin from the normal mean for gestation into mild (haemoglobin deficit less than 2 g/dl), moderate (deficit 2-7 g/dl), and severe (deficit greater than 7 g/dl).