London, Jan 30 (IANS): Researchers have found that infants of mothers who smoke during early pregnancy appear to have a small increased risk of fractures during the first year of life.

Many studies have found a link between smoking during pregnancy and growth problems in infants. But evidence of the impact of smoking during pregnancy on the bone health and risk of fractures in children at different stages of life is scarce and inconsistent.

"The results of this study indicate that maternal smoking during pregnancy is associated with an increased risk of fractures before one year of age," said study authors from Orebro University in Sweden.

Prenatal exposure to cigarette smoke, however, does not seem to have a longer-lasting biological influence on risk of fracture later in childhood and up to early adulthood," they added.

For the findings, published in the journal The BMJ, the research team set out to study the impact of maternal smoking during pregnancy on fractures in offspring from infancy to young adulthood.

Their findings were 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. Offsprings were followed up from birth to an average age of 21 (maximum age 32 years).

During this period 377,970 fractures were identified (a rate of 11.8 per 1,000 person years), the study said. 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 1,000 person years compared with 1.28 per 1,000 person years in those not exposed -- a small difference in fracture rate of 0.31 per 1,000 person years in the first year of life.

This association followed a dose-dependent pattern (compared with no smoking, there was a 20 per cent increased risk for 1-9 cigarettes/day and a 41 per cent increased risk for 10 or more cigarettes/day) and persisted after adjusting for shared familial factors in sibling analyses.

According to the study, maternal smoking during pregnancy was also associated with an increased fracture risk in offspring from age 5 to 32 years.