BOSTON — Prenatal smoking exposure is associated with significant increases in irritability in newborn girls but not boys, according to a study presented at a meeting of the Society for Research in Child Development.
The fact that significant differences were not evident in male infants in the large, epidemiologic sample might suggest early links to later sex differences in behavioral outcomes, said Rachel L. Paster, a research assistant in the Centers for Behavioral and Preventive Medicine, Brown University, Providence, R.I.
All of the infants exposed to prenatal smoking exhibited increases in muscle tension, compared with unexposed infants, she said in a poster presentation.
Using data from the New England Cohort of the National Collaborative Perinatal Project (NCPP), Ms. Paster and colleagues examined the effects of smoking during pregnancy on the neurobehavior of male and female newborns in a sample of 991 healthy mother-infant pairs recruited between 1959 and 1962.
As part of the NCPP, smoking was measured prospectively at each prenatal visit and newborn neurobehavior was assessed using the Graham-Rosenblith behavioral examination. For the current investigation, the participants were classified as nonsmokers, moderate smokers (between 1 and 19 cigarettes per day), and heavy smokers (20 or more cigarettes per day).
“We found significant differences between smoking groups for irritability in females, but not in males,” Ms. Paster reported. “Tests revealed significant differences between the heavy smoking group and both the moderate and no smoking groups only for female infants, while significant effects of maternal smoking group on muscle tone emerged for both male and female infants.”
The tests also showed different patterns of effects for males and females with respect to muscle tone. “For females, the heavy smoking group was significantly different from both the moderate and no smoking groups, whereas for males, the moderate smoking group differed significantly from the no smoking and heavy smoking groups,” said Ms. Paster.
Regarding the irritability findings, excessive irritability could indicate an infant withdrawal syndrome, Ms. Paster noted. Additionally, “irritability could potentially affect bonding and attachment with caregivers and may represent an early link to emotional dysregulation,” she said.