High cholesterol could make it difficult for women to become pregnant.

A study showed that couples in which both partners had high cholesterol took the longest to get pregnant, a National Institutes of Health news release reported.

"We've long known that high cholesterol levels increase the risk for heart disease," the study's first author, Enrique Schisterman, Ph.D., chief of the Epidemiology Branch at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), said in the news release. "In addition to safeguarding their health, our results suggest that couples wishing to achieve pregnancy would improve their chances by first ensuring that their cholesterol levels are in an acceptable range."

Cholesterol is a "waxy, fat-like substance" that is found in human cells; it makes hormones and vitamin D. High cholesterol can increase the risk of heart disease.

A research team looked at 501 couples who participated in the Longitudinal Investigation of Fertility and the Environment (LIFE) study to make their findings. The women involved in the study were between the ages of 18 and 44. The couples were followed for one year of trying to conceive.

The researchers measured the levels of cholesterol in the blood of each participant. Since cholesterol is used to manufacture sex hormones such as testosterone and estrogen, a connection with fertility makes sense.

The team analyzed the couple's chance of conceiving using the fecundability odds ratio (FOR), which looks at serum cholesterol concentrations to make its predictions.

 Couples in which the female had high cholesterol and the male did not also took longer to get pregnant than those with normal levels. Hispanic males were found to have the highest free cholesterol levels on average.

"From our data, it would appear that high cholesterol levels not only increase the risk for cardiovascular disease, but also reduce couples' chances of pregnancy," Dr. Schisterman said.