The reason some girls think that they can't get pregnant is probably a combination of factors, Finer explained.
"The risk of becoming pregnant from one act of sex is relatively small," he noted. "It may be the case that, for some teens, they had unprotected sex and didn't become pregnant so then they think they won't become pregnant based on their past experience," he said.
"This is a lack of recognition that if you don't get pregnant one time you may get pregnant at another time," Finer pointed out. In addition, some girls may think that either they or their partner is infertile.
Finer said more education about pregnancy and contraception is needed.
Another co-author of report pointed out other scenarios that might explain why these teens did not use contraception.
"Other reasons for not using contraception were their partner did not want to use it, or because they didn't mind getting pregnant," said Ayanna T. Harrison, who is also with the Division of Reproductive Health.
Among teens who got pregnant despite saying they used birth control, 24 percent said they used condoms and 21 percent said they used an IUD, implant or a birth control pill, said Harrison.
"When we looked at age, race and ethnicity, we didn't see a huge difference," Harrison said. However, among those who thought they couldn't get pregnant, 42 percent were Hispanic compared to almost 27 percent of white teens and 32 percent of black teens, she said.
Gavin added that most were not using the most effective methods of birth control, such as IUDs.
"They were using methods that require some kind of ongoing behavior, such as taking a pill every day or using a condom every time you have sex," she said. "We know that consistent use of the pill or a condom is a major problem."
Efforts are needed to dispel myths about becoming pregnant and to increase motivation to avoid pregnancy, Gavin said.
"We need to do a
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