Smoking in pregnancy and children’s mental and motor development at age 1 and 5 years

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Abstract

We used data from a Scandinavian prospective multicenter study to investigate if smoking in pregnancy may have an adverse effect on the child’s mental and motor abilities. Eligible for enrolment were para 1 and 2 women with a singleton pregnancy, who resided in one of the study areas and could be registered before the 20th gestational week. Women were classified as ‘smokers’ or ‘non-smokers’ at study start. At 13 months, 376 children (124 children of smokers) were evaluated with the Bayley Scales of Infant Development. At this age, children of smokers and non-smokers performed equally well. At 5 years, 369 children (132 children of smokers) were tested with the Wechsler Preschool and Primary Scales of Intelligence Revised (WPPSI-R), and 362 children with the Peabody Developmental Motor Scales (PDMS). Children of smokers had an increased risk of getting a WPPSI-R score below the median value of the population (OR=2.1, 95% CI: 1.2–3.3), but the risk was reduced when we adjusted for maternal education (OR=1.6, 95% CI: 0.9–3.7). Children of smokers had an increased risk of getting a test score below the median population value on the subscale ‘balance’ from PDMS (OR=1.8, 95% CI: 1.2–2.8). Thus, we found that smoking in pregnancy was associated with a small, but demonstrable adverse effect on the child’s balance at 5 years, whereas the negative effect on cognitive function did not reach statistical significance, when we adjusted for the mother’s level of education.

Introduction

Several studies have found that smoking in pregnancy is associated with intrauterine growth retardation and low birth weight [1], [2]. Further, children of smokers have been shown to have an increased frequency of SIDS, respiratory infections, acute exacerbations of asthma, otitis media [3], and hospitalisation in the first year of life [4].

With few exceptions [5], [6], [7], [8], most studies show that children of smokers perform slightly poorer on tests of mental development and behavioural outcome, compared to children of non-smokers [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. However, a number of confounders may be a problem in such studies. Rantakallio found that smoking was more common in groups with low soscioeconomic status. Mothers who were smokers tended to be younger, have shorter education, and were more likely to have an unexpected pregnancy than their non-smoking peers [13]. In some studies, the link between smoking in pregnancy and the child’s cognitive function seem to be entirely due to confounding [17], [21], [22], [23], [24].

The purpose of the present study was to measure possible differences in mental and motor development at age 1 and 5 years, between children whose mothers were smokers or non-smokers during pregnancy. We aimed to test the following hypotheses:

  • 1.

    Smoking in pregnancy has no effect on mental and psychomotor development at age 13 months, as measured with the Bayley Scales of Infant Development (BSID) [25].

  • 2.

    Smoking in pregnancy has no effect on cognitive development at age 5 years, as measured with the Wechsler Preschool and Primary Scales of Intelligence (WPPSI-R) [26].

  • 3.

    Smoking in pregnancy has no effect on motor skills at age 5 years, measured by the Peabody Developmental Motor Scales (PDMS) [27].

Section snippets

Study design

This study is part of a population based prospective study in Trondheim and Bergen, Norway, and Uppsala, Sweden. Details of the study have been reported elsewhere [28].

Enrolment took place between January 1986 and March 1988. Eligible were para 1 and para 2 women (i.e. women with one or two previous births, respectively) of Caucasian origin who had a singleton pregnancy and who could be registered prior to the 20th gestational week. At study entry, the women gave information about smoking

Development at age 13 months

Children of smokers and non-smokers performed equally well on BSID: the mean mental developmental index was 114±13 (mean±S.D.) and 116±11 for children of smokers and non-smokers, respectively. The mean psychomotor developmental index was 105±14 for children of smokers and 107±14 for children of non-smokers.

Cognitive development at age 5 years

IQ values obtained from the WPPSI-R test are summarised in Table 2. Mean total IQ was 105 for children of smokers, compared to 111 in the non-smoking group (P<0.001).

The median values of the

Development at age 13 months

Based on the BSID assessment, children of smokers had no increased risk of poorer mental or psychomotor development than children of non-smokers.

Previous studies of smoking in pregnancy and BSID results are inconsistent and inconclusive. In a study of more than 40 000 pregnant women, there was a roughly linear, approximate dose–response relationship between increasing cigarette consumption and low BSID scores at age 8 months [9]. In keeping with this result, another study found that prenatal

Conclusion

We have found that smoking in pregnancy may have a small adverse effect on the child’s balance score at 5 years of age. We were unable to demonstrate a statistically significant effect upon cognitive function, when we adjusted for the mother’s level of education. However, our results may be consistent with the results of larger studies that suggest that smoking in pregnancy still have a negative, but small effect on the child’s cognitive function.

Acknowledgements

This study was supported by the US National Institute of Child Health and Human Development, NIH (NICHD contract no. 1-HD-4-2803, and no. 1-hd-1-3127).

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