Respiratory Distress Syndrome in the Newborn: Relationship to Serum Prolactin, Thyroxine, and Sex

Abstract

Prolactin and thyroxine levels were measured by radioimmunoassay in cord blood of 61 premature infants of 26–36 weeks gestation. 30 of the infants subsequently developed respiratory distress syndrome (RDS). The infants who developed RDS had a mean cord prolactin level of 174.5 ± 24.5 ng/ml and a mean cord thyroxine level of 5.9 ± 0.4 μg/dl. In the 31 healthy infants, the mean cord prolactin and thyroxine levels were significantly higher (226.3 ± 25.8 ng/ml and 7.1 ± 0.4 μg/dl, respectively). The correlation coefficient between prolactin and thyroxine was r = 0.56 in infants with RDS (p < 0.0008). Both prolactin and thyroxine correlated with gestational age in the RDS group (r = 0.71 and 0.47, respectively). Discriminant analysis shows that the correlation between prolactin and thyroxine is independent of gestational age (r² = 0.32, p < 0.05). There was no correlation between the levels of prolactin and thyroxine in infants without RDS. In the healthy group, the cord prolactin levels were significantly higher (p < 0.01) in female (335.8 ± 47.7 ng/ml) than in male infants (209 ± 17.2 ng/ml). Premature infants who develop RDS have significantly lower thyroxine and prolactin levels in cord blood than infants who remain healthy.