A new study by USC researchers reveals that the mini-pill – progestin-only birth control pills – may put women who have had gestational diabetes at a higher risk of developing the chronic form of the disease.

“It appears that progestin-only oral contraceptives increase risk by nearly three-fold and should not be widely prescribed in this group of women,” said Siri Kjos, USC associate professor of obstetrics and gynecology.

That caution, however, is tempered by good news.

“The most important finding is that low-dose combination oral contraceptives appear to be a relatively safe method of contraception for these very high-risk women,” Kjos said. The USC team reports its results in the August 12 issue of the Journal of the American Medical Association.

For women who develop diabetes during pregnancy, family planning is critical. Yet, until now, it has not been clear how safe birth control pills are in these high-risk women.

In earlier studies, the USC team showed that women with a history of gestational diabetes mellitus (GDM) who have a subsequent pregnancy face a two-to-three-fold risk of developing chronic diabetes. Contraception is also important for the health of the fetus – if a woman unknowingly gets pregnant while her diabetes is untreated, her fetus faces an increased risk of birth defects, and she is more likely to miscarry or suffer other potentially fatal complications.

For women who wish to breastfeed and take hormonal contraceptives, doctors usually prescribe progestin-only oral contraceptives because they do not interfere with milk production. Low-dose combination birth control pills are more commonly used and contain a mix of estrogen and progestin.

In the study, USC researchers followed 904 Latina women who had developed GDM during a recent pregnancy, but whose ability to process sugars had returned to normal after delivery.

During their initial post-partum visits, about half chose to use hormonal oral contraceptives and half chose a non-hormonal form of contraception. Of the women opting to take birth control pills, 383 were prescribed low-dose combination birth control pills and the 78 women who were breastfeeding received the progestin-only mini-pill.

The research team found that 169 women developed chronic diabetes during the study and that the risk was influenced by the type of contraception they had used.

Of the women taking the progestin-only mini-pill, an average of 26.5 percent per year developed type 2 diabetes, compared to a rate of only 8.7 percent per year of women using non-hormonal contraceptives and 11.7 percent per year of those choosing a low-dose combination birth control pills.

“We found that the longer a woman used the progestin-only oral contraceptives, the higher her risk of later getting diabetes,” Kjos said.

The take home message? “It’s OK to take low-dose combination oral contraceptives even if you have had gestational diabetes,” said Ruth Peters, USC professor of preventive medicine, who helped lead the study. “But while you’re breast feeding, it’s probably better to use a non-hormonal form of contraception rather than the progestin-only mini-pill.”

Type 2 or adult-onset diabetes strikes more than 14 million Americans. Because many patients have no symptoms in its early stages, many unknowingly have the disease for years before being diagnosed by a blood test.

Risk factors include age, obesity, having a close relative with the disease and being a member of certain ethnic groups, such as Latino or African-American. Without treatment, type 2 diabetes can lead to serious complications including heart disease, stroke, nerve disease, vision problems and kidney failure. Early detection is important since lifestyle changes and oral medications can effectively control the disease.

Kjos, S.L.; Peters, R.K.; Xiang, A.; Thomas, D.; Schaefer, U.; Buchanan, T.A. “Contraception and the Risk of Type 2 Diabetes Mellitus in Latina Women With Prior Gestational Diabetes Mellitus.” JAMA, August 12, 1998, Vol. 280, No. 6, p. 533-8.