Hydration in the first 24 h of postnatal life in normal infants born vaginally or by caesarean section.

A total of 65 infants, 48 born vaginally and 17 by segment caesarean section, were studied prior to labour for extracellular volume (ECV) (corrected bromide space) and total body water (TBW) (deuterium space) during the first 24 h of postnatal life. The infants were mature and growth retardation excluded. A 'heel stick' blood sample was taken for micro determination of Br and urine for 2H2O concentration. ECV varied from 343 +/- 27 ml/kg at 6 h to 358 +/- 21 ml/kg at 24 h and TBW was 75.5 +/- 3.4% of body weight. Contrary to current opinion, neither TBW nor cell hydration differed in infants born by caesarean section compared with those born vaginally. Such modern methodology to study infant body hydration and the critical assessment of growth and maturity demonstrates that hydration during the first 24 h of life is relatively stable and is not affected by the mode of delivery.