Smoking during pregnancy and diabetes mellitus in a British longitudinal birth cohortBMJ 2002; 324 doi: https://doi.org/10.1136/bmj.324.7328.26 (Published 05 January 2002) Cite this as: BMJ 2002;324:26
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Linda Palmer raises the valid possibility of confounding in our study
of smoking during pregnancy and type 2 diabetes mellitus in offspring.
She suggests that a mother who smokes during pregnancy may be less likely
to breast feed her infant and it may be this, rather than maternal smoking
itself, that increases the risk of diabetes. It is possible to test this
hypothesis, as information on breast feeding was collected by the National
Child Development Study (NCDS) which recorded if the child was breast fed
and if breast feeding was for up to one month or over one month in
Adding the breast feeding variable to the adjusted analysis described
previously had little impact on the estimates. After adjustment for
maternal smoking during pregnancy, sex, mother’s age at birth of cohort
member, age mother left school, family social class at birth, birth
weight, own smoking at age 16 years, BMI at age 33 years and duration of
breast feeding, the odds ratios (with 95% confidence intervals) for
diabetes associated with maternal smoking are: 1.15 (0.34 to 4.20), 4.26
(1.31 to 13.83) and 4.62 (1.85 to 11.51) for medium, variable and heavy
smokers, respectively, when compared with non smokers. There is no
statistically significant association of breast feeding with diabetes.
Compared with mothers who never breast fed their infant, the adjusted odds
ratios for diabetes associated with breast feeding for up to or over a
month are 0.91 (0.31 to 2.72) and 1.29 (0.52 to 3.17), respectively.
Breast feeding pattern is not statistically significantly associated with
obesity at age 33 years (p=0.288) in the adjusted model, while the
estimates for maternal smoking are unaltered.
Additionally, the influences of maternal smoking during pregnancy and
breast feeding pattern on obesity at age 23 years (BMI >30) among those
without a diagnosis of diabetes were examined. After adjustment for the
all of the potential confounding factors listed above (except BMI at 33),
breast feeding was not statistically significantly associated with obesity
at age 23 years, with odds ratios for obesity associated with breast
feeding for up to or over a month of 0.45 (0.06 to 3.74) and 0.47 (0.06 to
3.78), respectively. Compared with those who had non-smoking mothers, the
risk of obesity was significantly increased by maternal smoking with
adjusted odd ratios for obesity of 1.55 (0.97 to 2.47) 2.02 (1.07 to 3.82)
and 2.56 (1.63 to 4.02) for medium, variable and heavy smoking in mothers,
These results provide further evidence that maternal smoking during
pregnancy may have a direct influence on the risk of diabetes mellitus and
obesity in offspring. The higher risk of maternal smoking for obesity at
age 23 years, compared with obesity at age 33 years is of interest and may
reflect the influence of earlier onset metabolic dysregulation due to in
utero exposures. By age 33 years other, adult, factors may be diluting the
influence of earlier exposures on non-diabetic obesity.
1. Montgomery SM, Ekbom A. Smoking during pregnancy and diabetes
mellitus in a British longitudinal birth cohort. British Medical Journal
BMJ 2002; 324:26-27.
Competing interests: No competing interests
I would like to see an examination of the infant-feeding
relationships to smoking mothers and consequent diabetes in their
offspring. The mother who chooses to smoke during pregnancy is also far
less likely to make the health-protecting decision to breastfeed her
infant. Many studies reveal that the age and level of exposure to
artificial infant feeds, especially bovine derived, strongly correlates to
the risk of developing diabetes mellitus.
Competing interests: No competing interests