Reference intervals for haematological variables during normal pregnancy and postpartum in 434 healthy Danish women

Abstract

Aim: To report reference intervals for haematological variables during normal pregnancy and postpartum.

Material and methods: The series comprised 434 healthy ethnic Danish women with a normal pregnancy > or =37 wk duration and a normal delivery with newborns weight >2500 g. Blood samples were obtained at 18, 32 and 39 wk gestation and at 8 wk postpartum. The following variables were analysed: Haemoglobin (Hb), haematocrit (Hct), blood erythrocyte count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, white cell count, platelet count, erythrocyte folate, plasma folate, plasma cobalamin, plasma methylmalonic acid, plasma total homocysteine, serum ferritin, serum soluble transferrin receptor and plasma creatinine. Reference intervals were calculated using log(10)-transformed values (which showed normal distributions) as mean +/- 1.96 x SD.

Results: The lower reference value for Hb during pregnancy was 6.45 mmol/L (105 g/L) and 7.3 mmol/L (118 g/L) postpartum. The lower reference value for Hct was 0.31 in pregnancy and 0.35 postpartum. There was a gradual decline in the lower reference value for erythrocyte folate during pregnancy and postpartum from 0.46 to 0.29 micromol/L and in plasma folate from 6 to 4 nmol/L. Lower reference value for plasma cobalamin declined during pregnancy from 96 to 71 pmol/L, but increased postpartum to 148 pmol/L. Upper reference value for plasma homocysteine increased gradually during pregnancy and postpartum from 11.0 to 20.6 micromol/L. Geometric mean serum ferritin at 18 wk gestation was 32 microg/L. Plasma creatinine values were low during pregnancy and displayed a significant increase postpartum.

Conclusion: The characteristic changes occurring in haematological indices during pregnancy and postpartum are described in this study. The results may be used as reference values in the assessment of health status of pregnant women with a similar socio-economic and racial background.