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Research we're watching

Women who use marijuana may have more difficulty getting pregnant than women who don't, according to a study published online Jan. 11, 2021, by the journal Human Reproduction.

The study looked at 1,200 women who were trying to conceive after experiencing either one or two miscarriages. The researchers followed the women for six monthly cycles and tracked those who became pregnant for the duration of their pregnancy. Those who reported using marijuana or hashish in the past 12 months or whose urine samples showed evidence of cannabis were 40% less likely to get pregnant during each monthly cycle than those who didn't use cannabis. Only 42% of the cannabis users became pregnant during the study period, compared with 66% of non-users. There did not, however, appear to be any difference in miscarriage rate between users and non-users. The study authors said that further research is needed to confirm the results.

Preterm birth joins other pregnancy-related conditions as potential heart risk factors.

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Preterm birth has long been known to bring health risks for the baby, but it may also bring risks for the mother. A study in the June issue of Hypertension shows that women who gave birth to a baby before 37 weeks of pregnancy were more likely to experience rising blood pressures later on compared to women who delivered closer to term. If they had this pattern, they were also more likely to show signs of coronary artery disease, which is associated with an increased risk of heart attack and stroke.

Because of the unique demands that pregnancy places on a woman's body, it may serve as a stress test for the female heart, says Dr. JoAnn E. Manson, the Michael and Lee Bell Professor of Women's Health at Harvard Medical School. In the May issue, we talked about how other pregnancy-related conditions � gestational diabetes, pre-eclampsia (a type of pregnancy-induced high blood pressure), and other pregnancy-related hypertensive disorders � can raise a woman's risk of developing cardiovascular disease. Preterm birth should now join that list, says Dr. Manson.

Doctors typically recommend that women who have high blood pressure avoid using birth control that contains estrogen to avoid raising risks for a stroke or heart attack. According to a clinical update, this recommendation may be changing for some women with high blood pressure.

Overall risk is very small, and older women who used hormonal contraceptives many years ago aren't likely to have a higher risk.

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Hormonal birth control � whether it comes as pills, injections, a ring, an intrauterine device (IUD), or an implant � may raise your risk of breast cancer, according to a study published Dec. 7, 2017, in The New England Journal of Medicine.

If you're like many women who currently use one of these contraceptive methods, or if you used one for years in the past, should you be worried?

Research we're watching

If a woman has gestational diabetes during her pregnancy, she has a higher risk of developing diabetes later. But a study published February 10 in Diabetes Care found that breastfeeding may help reduce that risk.

The study, which used data from the Nurses' Health Study II, found that the longer a woman nursed her infant, the lower her risk of developing diabetes later in life. The study included more than 4,000 women who had gestational diabetes. Of those women, more than 800 developed diabetes within the next 25 years. Those who breastfed for six to 12 months were 9% less likely to develop diabetes, compared with women who didn't breastfeed at all. Women who breastfed for one to two years had a 15% lower risk of developing diabetes, compared with women who didn't breastfeed. And diabetes risk was 27% lower in women who breastfed for more than two years. This provides another reason that doctors may want to encourage women with gestational diabetes to breastfeed whenever possible.