Just because heart disease risk factors are associated with infertility doesn’t mean they cause infertility.
Young women with unhealthy levels of fats in their blood may have higher odds of having just one child, or no children at all, a recent study suggests.
Dr. Aleksandra Pirnat at the University of Bergen in Norway and her colleagues studied women enrolled in two large databases: the Medical Birth Registry of Norway and the Cohort of Norway, which include lifestyle and health information for people residing in the country between 1994 and 2003.
Of the 4,322 women in the study, 2,157 had two or more children, 488 had just one child, and 1,677 were childless.
The researchers found that childless women and one-time moms differed from the women with multiple children in some significant ways. They tended to be older and heavier, and they were more likely to have diabetes and to smoke. They also had fewer years of education and were more likely than women with at least two children to have turned to in vitro fertilization for help getting pregnant.
Even after accounting for these and other factors, women with two or more children were more likely to have had healthy levels of lipids in their blood before their first pregnancy, compared to those with one or no children.
Blood tests for lipids typically measure levels of “good” HDL cholesterol, “bad” LDL cholesterol, total cholesterol and triglycerides. Unhealthy levels are one of the major controllable risk factors for heart disease and stroke, according to the American Heart Association. The AHA warns that in people with other risk factors such as smoking, high blood pressure or diabetes, high lipid levels increase the risk for heart disease and stroke even more.
The new research, published in BMJ Open, can’t prove whether or how unhealthy lipid levels might impact pregnancy.
The study “is interesting and one that raises a lot of questions,” said Dr. Katie Berlacher, a cardiologist at the University of Pittsburgh Medical Center and director of the Women’s Heart Program at UPMC Magee-Womens Hospital. “But what they’ve found is only an association.”
Just because heart disease risk factors are associated with infertility doesn’t mean they cause infertility, Berlacher explained.
Also, even if the association were proven to be true for Norwegians, it might not be for Americans, said Berlacher, who was not associated with the new study. “Norway has a very homogenous population,” Berlacher said. “That makes it hard to apply to other countries, like America.”
Another possible issue is that some of the women who had only one child or who remained childless might have done so by choice, Berlacher said. Without talking to the women, there’s no way of knowing.
While acknowledging that more studies need to be done, Pirnat does have some advice for women trying to get pregnant in the meantime.
“For women who have problems conceiving - with their first child or second - it might be useful to check their lipids, especially if they have someone in their family with higher lipids,” she told Reuters Health. “They could talk to their doctors about some beneficial diets, the Mediterranean, for example, and introduce other changes in lifestyle that can lower lipid levels, such as physical activity.”