New York, July 1 (IANS): Compared to their normal-weight peers, obese adolescents are significantly less likely to use contraception, putting them at higher risk of unintended pregnancies, says a new study.

"Our findings suggest that obesity may be an important factor associated with adolescent women's sexual behaviour," said lead author Tammy Chang, assistant professor of family medicine at University of Michigan Medical School in the US.

The researchers measured contraceptive use from a longitudinal study of 900 women ages 18-19 in Michigan.

"Understanding sexual behaviours by weight status among adolescents is critical because of the risk of dangerous outcomes for moms and babies associated with obesity," Chang said.

While differences in contraception use are significant between obese girls compared to their normal weight peers in the new study, researchers found no differences in other sexual behaviours, including number of partners, frequency of sex or length of relationships.

However, the authors noted that obese adolescents have been shown to differ from normal-weight peers in several ways, including having lower self-esteem -- which may hinder preparing for sex -- asking clinicians for contraceptives or obtaining contraception -- from a pharmacy.

One quarter of all US women become pregnant at least once by the age of 20.

"Reducing adolescent pregnancy is a national public health priority and we need to understand which adolescents are at higher risk of pregnancy," Chang said.

The study appeared in the Journal of Paediatrics.