Increased cortisol concentrations in the cord blood of newborns whose mothers smoked during pregnancy

To investigate the effect of tobacco smoke on cord blood cortisol concentrations.

Cortisol concentrations were measured in cord blood from 211 term newborns of smoking and 211 term newborns of nonsmoking mothers; 48 and 36 newborns were delivered by cesarean section, respectively. In 16 cases, in addition to cord blood, maternal venous blood was obtained at delivery.

The median cord blood cortisol concentration in neonates of the smoking and the nonsmoking mothers was 23 and 13 microg/dL, respectively (P<0.0001). Cortisol concentrations were greater in the newborns whose mothers smoked, when compared to corresponding controls, whether they were delivered vaginally or by cesarean section. In the newborns delivered by cesarean section, there was a positive correlation between number of cigarettes smoked/day and cortisol concentrations, as well as a negative correlation between cortisol concentrations and neonatal length. There was no significant correlation between cortisol concentrations and birth weight or head circumference. Cortisol concentrations in the cord blood of neonates whose mothers were smokers and nonsmokers were by 29% and 45% lower from those measured in their mothers, respectively.

Although a causal relationship between maternal smoking and high cortisol concentrations in cord blood was not established, the findings are in accordance with previous reports indicating elevated stress-hormones in newborns whose mothers smoked during pregnancy.