Effects at age nine of maternal smoking in pregnancy: experimental and observational findings

Abstract

Objectives: To compare long term outcomes of a randomised controlled trial of anti-smoking education in pregnancy and to examine the same outcomes according to maternal pregnancy smoking behaviour.

Design: Follow up of the population included in the randomised controlled trial nine years later and of ex-smokers and non-smokers within the same hospital population.

Setting: A maternity hospital in Birmingham with follow up of children in schools and mothers at home.

Population: 1218 smokers recruited to the trial; also 191 ex-smokers at booking and 414 non-smokers throughout pregnancy.

Methods: Children were assessed individually by psychologists in schools, and mothers interviewed at home to obtain additional information relevant to cognitive development and growth. Information on smoking during pregnancy was obtained from mothers and obstetric data from computerised case-notes, both recorded immediately following delivery.

Main outcome measures: Height, weight, IQ and neurological soft signs at 9.4 years.

Results: Differences in birthweight and length between the intervention and control groups were confirmed but no intervention-control differences were found at age 9.4 for weight, height, IQ or neurological soft signs. Differences were found for height and IQ according to mothers pregnancy smoking behaviour, but smoking did not remain an independent predictor after taking account of confounding factors. Alternative classifications of smoking behaviour, taking account of the gestation at stopping and mean cigarette consumption throughout pregnancy likewise showed no effect.

Conclusions: The well established early hazards of smoking during pregnancy seem to be resolved by later childhood, with no evidence of direct long term effects on growth or cognitive functioning.