Newswise — ANN ARBOR, Mich. — A study of nearly 1,000 teens found that sexually active obese adolescents were significantly less likely to use contraception than normal weight peers, putting them at higher risk of unintended pregnancy.

Obese adolescents who did use contraception were also less likely to use it consistently, according to the University of Michigan Health System study that appears in The Journal of Pediatrics.

Researchers analyzed 26,545 weekly journal surveys measuring sexual practices and contraceptive use from a longitudinal study of 900 women ages 18-19 in Michigan. They examined the association between weight and sexual behaviors.

“The U.S. teen pregnancy rate is one of the highest in the developed world and we know pregnant adolescents are more likely to have poor birth outcomes,” says lead author Tammy Chang, M.D., MPH, MS, an assistant professor of family medicine at the U-M Medical School and member of the U-M Institute for Healthcare Policy and Innovation.

“Reducing adolescent pregnancy is a national public health priority and we need to understand which adolescents are at higher risk of pregnancy. Our findings suggest that obesity may be an important factor associated with adolescent women’s sexual behavior.”

One quarter of all U.S. women become pregnant at least once by age 20. The U-M study focused on women ages 18-19, ages that are linked to the highest rates of unintended pregnancy. A previous study led by Chang found that women who give birth as adolescents are at an increased risk for obesity later in life.

Obese women who become pregnant have a higher risk for gestational diabetes, hypertensive disorders, blood clots, Cesarean-sections, stillbirths and birth-related injuries. Their infants are also more likely to be admitted to the neonatal intensive care unit. One fifth of U.S. adolescents are obese.

“Understanding sexual behaviors by weight status among adolescents is critical because of the risk of dangerous outcomes for moms and babies associated with obesity,” Chang says.

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 behaviors, including number of partners, frequency of sex or length of relationships.

Authors note 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. Lower levels of contraceptive use may also be connected to socioeconomic barriers and limited health literacy that are risk factors for obesity itself. “By understanding the barriers that put certain groups of teens at higher risk of unintended pregnancies, clinicians and researchers can tailor interventions to empower adolescents to make healthier sexual choices,” Chang says.

Additional Authors: Matthew Davis, M.D., MAPP; Yasamin Kusunoki, Ph.D., M.P.H.; Elizabeth Ela; Kelli Hall, Ph.D., M.S.; Jennifer Barber, Ph.D, all of U-M.

Funding: National Institute of Child Health and Human Development (R01 HD050329, R01 HD050329-S1, R24 HD041028, and T32 HD007339)

Disclosure: None

Reference: “Sexual Behavior and Contraceptive Use Among 18 to 19 year old Adolescent Women By Weight Status: A Longitudinal Analysis,” July 1, 2015, The Journal of Pediatrics.