OB/GYN Krista Johnson says that while there are some women whose pill is more effective than others, she finds it hard to understand why a particular brand is so effective at preventing ovarian cancer in women who don’t use it.

Johnson, a professor at the University of Michigan, has spent much of her career researching the effects of birth control pills on ovarian cancer risk.

Johnson says the new study, published in the Journal of the American College of Obstetricians and Gynecologists, shows that women who take the pill at least every two years are at a higher risk of ovarian cancer than those who don, but it’s not yet clear why.

A study published in April by researchers at the National Cancer Institute and the National Institute of Allergy and Infectious Diseases found that women with regular use of oral contraceptives had a slightly lower risk of dying from ovarian cancer compared with women who didn’t use them.

Johnson said it’s possible that oral contraceptives could act on the same mechanisms that other birth control methods do.

“The way they work is that they interact with hormones,” Johnson said.

“And when that happens, the risk increases.”

The study involved 1,700 women, including 446 women who had never used the pill.

The researchers also asked the women if they had ever used the Pill or had had a negative pregnancy test.

“We also asked whether they had used the progestin IUD,” Johnson explained.

“What we found was that women were using the pill for a lot longer periods of time, so that’s probably what we think is going on.”

The researchers found that while the women who took the pill were more likely to die from ovarian cancers than those not using it, the pill was not the only factor in their increased risk.

The women who used the pills were also more likely than those without them to have a history of hormone treatment that could lead to a hormonal imbalance.

And while the study didn’t include information about specific types of oral contraceptive, Johnson said the findings suggest that oral contraceptive use is linked to a higher incidence of ovarian cancers.

“It’s a bit of a puzzle,” she said.

Johnson hopes the study will help researchers better understand the role of hormonal imbalances in ovarian cancer, and will help prevent unintended pregnancies among women who are using the Pill.

She said it would also help women who have been taking the pill but are experiencing an unwanted pregnancy.

“When you’re trying to get pregnant, you have a lot of hormones in your body, and your body has been trying to figure out how to manage these hormones,” she explained.

The findings suggest the use of birth prevention pills could be helpful for preventing ovarian cancers in women in certain situations.

For instance, if you’re experiencing an unexpected pregnancy or you have other hormonal problems, the researchers suggest taking the Pill to reduce the risk of a second pregnancy, and to reduce your risk of experiencing an ectopic pregnancy.

But it could also reduce the overall risk of ovaries developing ovarian tumors, Johnson noted.

She also noted that the study doesn’t include any information about whether people who were using oral contraceptives during pregnancy or during a miscarriage were at increased risk for ovarian cancer if they took the Pill before or after the miscarriage.

“If we were to take that data into consideration, we don’t know whether there’s any increase in the risk, or if there’s no increase,” Johnson told ABC News.

While the new findings aren’t conclusive, they do provide a window into how birth control has been used in recent decades, and how it might be influencing the development of ovarian tumors in women.

And Johnson said that there are still many unanswered questions about how birth prevention can be helpful in preventing ovarian tumors.

“There’s no good answer that we have right now, because we have a large body of evidence that shows that these hormonal imbalance have an effect on ovarian tumors,” she told ABCNews.com.

“So it’s just a matter of how much we know.”