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. 1999 Apr 3;318(7188):897-900.
doi: 10.1136/bmj.318.7188.897.

Twins and maternal smoking: ordeals for the fetal origins hypothesis? A cohort study

S Williams  1 , R Poulton
Affiliations

Twins and maternal smoking: ordeals for the fetal origins hypothesis? A cohort study

S Williams et al. BMJ. .

Abstract

Objective: To assess the direct and indirect effects of being a twin, maternal smoking, birth weight, and mother's height on blood pressure at ages 9 and 18 years.

Design: Longitudinal study.

Subjects: Cohort born in 1972-3.

Setting: Dunedin, New Zealand.

Main outcome measure: Blood pressure at ages 9 and 18 years.

Results: Compared with singletons, twins had a systolic blood pressure 4.55 (95% confidence interval 1.57 to 7.52) mm Hg lower at age 9 after adjustment for direct and indirect effects of sex, maternal smoking, mother's height, socioeconomic status, and birth weight, as well as concurrent height and body mass index. Blood pressure in children whose mothers had smoked during pregnancy was 1.54 (0.46 to 2.62) mm Hg higher than in those whose mothers did not. The total effect of birth weight on systolic blood pressure at age 9 was -0.78 (-1.76 to 0.20) mm Hg and that for mother's height was 0.10 (0.06 to 0.14) mm Hg. Similar results were obtained for systolic blood pressure at age 18. The total effect of twins, maternal smoking, and birth weight on diastolic blood pressure was not significant at either age.

Conclusions: Twins had lower birth weight and lower systolic blood pressure at ages 9 and 18 than singletons. This finding challenges the fetal origins hypothesis. The effect of maternal smoking was consistent with the fetal origin hypothesis in that the infants of smokers were smaller and had higher blood pressure at both ages. This may be explained by pharmacological rather than nutritional effects. The total effect of birth weight on systolic blood pressure, after its indirect effect working through concurrent measures of height and body mass index was taken into account, was small.

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Figures

Figure 1
Figure 1
Box and whisker plots for systolic blood pressure at age 9 and birth weight for twins compared with singletons, and children of mothers who smoked during pregnancy compared with children of mothers who did not smoke
Figure 2
Figure 2
Path diagram for effects of sex, being a twin, mother’s smoking, and mother’s height on birth weight, and their effects on height, body mass index, and systolic blood pressure at age 9 years
See this image and copyright information in PMC

Comment in

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