New research suggests that women choose to use contraception based on current relationships and sexual activity, not just pregnancy desires.

Researchers at Penn State College of Medicine found that partnership status and frequency of sexual intercourse, not long-term pregnancy intent, were the strongest predictors of prescription contraceptive use.

"Currently, oral contraceptives (the birth control pill) are the most commonly used contraception in the U.S. -- used by 16 percent of all women ages 15-44 -- while LARCs (long-acting reversible contraceptives, including intrauterine devices and implants) are used by only 7.2 percent," wrote researchers Cynthia Chuang and Carol Weisman.

For the study, researchers surveyed 1,000 women in Pennsylvania, all with private health insurance covering prescription contraception, on their contraception use -- including prescription and over-the-counter methods, as well as natural family planning and withdrawal. The women were also asked about their pregnancy intent, pregnancy history and pregnancy risk exposure.

The women surveyed were not planning on getting pregnant within at least the next 12 months. Thirteen percent of participants planned to have a pregnancy in the next 12 to 24 months; 25 percent in two to five years; 23 percent in five or more years; another 23 percent were not sure if or when they wanted to have a baby; and 16 percent said they did not ever intend to have a baby.

"We found that a lot of women who intend to get pregnant someday, but not for at least a year, were not using LARCs," Chuang said in a statement. "However, women who don't ever want to get pregnant are more likely to use long-acting reversible contraception."

The study is part of an ongoing randomized controlled trial to test an online intervention to help women make contraceptive choices consistent with their pregnancy plans.

The findings are detailed in the journal Contraception.