Pregnancies more likely in teens who smoke, drink and use drugs

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High school students who smoke, drink, use drugs, carry a weapon to school, get involved in fights or engage in other risky behaviors also are more likely to become pregnant or to impregnate a sexual partner, according to a new study from psychiatry researchers at Washington University School of Medicine in St. Louis.

And it wasn’t just one pregnancy, according to the study, published in the Journal of Adolescent Health.

“Teen pregnancies have been declining, but it’s not because teens aren’t engaging in as much sex, it’s that more have been using condoms and other contraceptive methods,” says first author Patricia A. Cavazos-Rehg, PhD. “Yet there’s still this high-risk group of adolescents putting themselves at increased risk for pregnancy and sexually transmitted infections.”


Cavazos-Rehg, research assistant professor of psychiatry, analyzed data gathered in 1999, 2001 and 2003 as part of the National Youth Risk Behavior Survey, a project that collected information from more than 14,000 high school students, who answered questions about smoking, drug use, drinking and driving, sexual activity and other risky behaviors.

Adolescents were asked if they were involved in 10 risky health behaviors, Cavazos-Rehg explains. Almost 20 percent of the boys reported that they engaged in at least seven of those 10, and about 10 percent of the girls also were engaging in the majority of these risky behaviors.

Teen Survey

In the past 30 days, have you…

  • carried a weapon
  • smoked cigarettes
  • smoked two or more cigarettes every day
  • drove after drinking
  • rode with a driver who had been drinking
  • drank alcohol
  • drank five or more alcoholic beverages in one sitting (binge drinking)
  • used marijuana
  • used cocaine
  • were involved in a physical fight in the last 12 months

“We found that those involved in risky activities had not only an elevated risk for pregnancy but also an even greater risk for multiple pregnancies, and as risky health behaviors occurred more frequently, so did pregnancies,” she says.

Because some 750,000 teens get pregnant the United States each year, Cavazos-Rehg says she wasn’t surprised that almost 8 percent of adolescent males had impregnated a partner and about 13 percent of females reported that they had experienced a pregnancy. What did surprise her, she says, was that so many had the experience more than once.

“I did expect some of this, but it was so much more pronounced than I would have thought,” she says. “I would have expected an adolescent would learn a lesson and then try to prevent another pregnancy from occurring in the future. But it appears that many of those most at risk are not attempting to modify their behavior after that initial pregnancy.”

Part of the explanation is revealed in data from a second study led by Cavazos-Rehg and published in the journal Contraception. In that study, her team found that substance-using males and females who had numerous sexual partners were the least likely to use contraceptives, putting them at risk for pregnancy and for sexually transmitted infections.

That study looked at substance use among teens and its relationship to contraceptive choices. The team correlated findings about smoking, drinking, marijuana and cocaine use with information about contraceptive use and found that adolescent males using all four substances were the least likely to use any contraceptive method.

Among girls in the study, those who reported having had six or more sex partners were more likely to use no contraception or to rely upon withdrawal as a way to prevent pregnancy.

These two studies probably underestimate the extent of the problem among adolescents because the surveys don’t include information from teens who dropped out of high school, according to Cavazos-Rehg. She says information from those who quit school almost certainly would inflate the numbers related to teen pregnancy and risky health behaviors.

Currently, her team is analyzing more information from teens to determine whether some pregnancies involving high-risk teenagers might be intentional rather than accidental, asking those adolescents whether they would be pleased or upset by a pregnancy.

Intentional teen pregnancies would be difficult to prevent, Cavazos-Rehg says, but better understanding the link between pregnancies and risky health behaviors could provide teachers, administrators and parents with a way to target adolescents most at risk for pregnancies and sexually transmitted infections.

“If a child is smoking or drinking or engaging in other risky behaviors, school counselors, educators and parents should not only target that particular behavior but also talk to the teen about sex,” Cavazos-Rehg says. “If a teen is engaging in these risky behaviors, he or she probably isn’t quite ready to be a parent yet, but those same teens appear to be the most likely to have a child.”

Cavazos-Rehg PA, Krauss MJ, Spitznagel EL, Schootman M, Cottler LB, Bierut LJ. Associations between multiple pregnancies and health risk behaviors among U.S. adolescents, Journal of Adolescent Health, vol. 47(6), Dec., 2010. pp. 600-603.

Cavazos-Rehg PA, Krauss MJ, Spitznagel EL, Schootman M, Peipert JF, Cottler LB, Bierut LJ. Type of contraception method used at last intercourse and associations with health risk behaviors among U.S. adolescents, Contraception, vol. 82(6), Dec., 2010. pp. 549-555.

This work was supported by grants from the National Center for Research Resources and the National Institute on Drug Abuse of the National Institutes of Health.

Washington University School of Medicine’s 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked fourth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.