Women who take newer types of birth-control pills face a higher risk of developing blood clots than women who take older types, researchers said, providing what some called “clarifying” evidence that more modern contraceptives designed as safer options may pose more risk than earlier formulations.

University of Nottingham researcher Yana Vinogradova and colleagues, examining two medical-records databases to study more than 50,000 15- to 49-year-old women in Britain, found, as researchers have known for decades, that women who took combined oral contraceptives (formulations that include versions of two hormones, estrogen and progestin) had a higher risk of developing venous thromboembolisms — dangerous blood clots — than women who don’t take the pill.

But when the team broke out the data by medication and controlled for other risk factors, they also discovered that certain versions of the birth-control pill were associated with higher risk.

Medications using the synthetic hormones drospirenone (found in Yasmin), desogestrel (found in Kariva and Mircette) and other newer formulations were associated with a 1.5 to 1.8 times higher risk than older drugs containing synthetic hormones, such as levonorgestrel.

The study, published Tuesday in the journal the BMJ, confirms past findings, said Susan Jick, an epidemiologist at the Boston University School of Public Health who wrote an editorial with the report.

Worldwide, Vinogradova and her co-authors wrote, nearly 10 percent of women of childbearing age use oral contraceptives, with 18 percent of women in developed countries using them. The risk of blood clots for such women, who are generally healthy, is low.

Drugmakers were trying to create safer pills by using the newer synthetic hormones like drospirenone.