Smoking during pregnancy may up fracture risk in babies: Study

Infants of mothers who smoke during early pregnancy appear to have an increased risk of fractures during the first year of life, according to a study.

The results, published in The BMJ, show no long-lasting effect on fracture risk later in childhood, and up to early adulthood.

This suggests that smoking in pregnancy only has a short term influence on bone health, the researchers said.

Many studies have found a link between smoking during pregnancy and growth problems in infants.

However, evidence of the impact of smoking during pregnancy on bone health and risk of fractures in children at different stages of life is scarce and inconsistent.

The researchers from the Orebro University in Sweden set out to study the impact of maternal smoking during pregnancy on fractures in offspring from infancy to young adulthood.

The findings are based on over 1.6 million people born in Sweden between 1983 and 2000 to women who smoked (377,367) and did not smoke (1,302,940) in early pregnancy.

Offspring were followed up from birth to an average age of 21. During this period 377,970 fractures were identified.

The researchers also carried out sibling comparison analyses to control for any unwanted effects of unmeasured familial -- genetic and environmental -- factors shared by siblings, making the results more likely to be reliable.

Overall, maternal smoking was associated with a higher rate of fractures in offspring before one year of age.

In absolute numbers, the risk of fracture in those exposed to maternal smoking was 1.59 per 1000 person years compared with 1.28 per 1000 person years in those not exposed -- a small difference in fracture rate of 0.31 per 1000 person years in the first year of life.

This is an observational study so can't establish cause, and the researchers point to some limitations, such as the possibility that some women will not admit smoking during pregnancy or might under-report the number of cigarettes smoked.

They said the data covered a large number of people and addressed risk of fractures during different developmental stages of life.

"The results of this study indicate that maternal smoking during pregnancy is associated with an increased risk of fractures before one year of age," the researchers said.