Lesbians are less likely to get timely cervical cancer screening than heterosexual and bisexual women, concludes a study by Rice University.

The study, “Cancer Screening Utilization Among U.S. Women: How Mammogram and Pap Test Use Varies Among Heterosexual, Lesbian and Bisexual Women,” appeared in Population Research and Policy Review.

Frequent screening is an important tool for reducing cancer mortality because it increases the chances of finding cancer at an early stage. For breast and cervical cancer, earlier detection usually means more successful treatment. But while pap and mammography screening rates are generally high among U.S. women, studies suggest that sexual orientation might influence the rates of breast and cervical cancer screening.

To examine this, researchers looked at data from 2,273 lesbian, 1,689 bisexual and 174,839 heterosexual women, all included in the Behavioral Risk Factor Surveillance System and interviewed in 15 states between 2000 and 2015. They focused mainly on two cancer-screening measures; women aged 40 and older who had received a mammogram in the past two years, and women aged 21-65 who reported having had a pap test in the past three years.

While the results showed no differences in the rates of timely mammograms in women with distinct sexual orientations, after adjusting for socioeconomic status, the researchers found that lesbian women were 25 percent less likely than heterosexual and bisexual women to get timely pap smears.

Alexa Solazzo, the study’s lead author, believes the use of birth control might explain the results.

“Many doctors require women who seek a birth-control prescription to have had a recent pap test,” Solazzo said in a news release. “Women who don’t have sex with men might theoretically have less of a need for birth control than women who do have sex with men (i.e., heterosexual or bisexual women). Thus, they may be less likely to seek care at an OB-GYN and receive a pap test.”

The team hopes its findings will encourage more studies on sexual-minority health disparities and lead to greater emphasis on the importance of having pap smears and mammograms regardless of sexuality.

“A straightforward change to the public health message women receive that focuses less on sexual activity and more on the long-term health benefits of pap-smear testing may improve health overall and help reduce differences by sexual orientation,” Solazzo said.