When both the prospective mom and dad had high cholesterol levels, it took longer to conceive compared to those with lower cholesterol levels. The study also found the highest cholesterol levels among the couples who didn't achieve pregnancy during the year-long study.
"This is the first time that cholesterol levels have been identified as a factor in pregnancy along with known factors, such as age and weight," said lead researcher Enrique Schisterman, senior investigator and chief of the epidemiology branch at the U.S. Eunice Kennedy Shriver National Institute of Child Health and Human Development.
Cholesterol is a waxy substance that can build up in the body's blood vessels, according to the U.S. National Heart, Lung, and Blood Institute. Genetics and your family history play a role in your cholesterol levels, but so too, do diet and exercise, the institute says.
Schisterman noted that when both the man and the woman have high cholesterol it takes much longer to conceive.
"If the woman has high cholesterol and the man has normal cholesterol, then it takes longer, but not as long as when both have high cholesterol," Schisterman said.
"When only the man has high cholesterol and the woman has normal levels, it doesn't seem to have an effect," he added.
Schisterman noted that while this study shows an association between cholesterol levels and time to conception, what isn't known is whether high cholesterol causes the delay.
It's also not clear if taking drugs to lower cholesterol would shorten the time to conception. "We don't know that yet. Our study was not designed to see the effect of statins," he said. Statins are medications used to lower cholesterol levels.
Also, it's possible that diet and exercise, which are known to lower cholesterol, might also reduce the time to conception, Schisterman said.
"Having a healthy diet, exercising and maintaining normal cholesterol levels will help couples become pregnant and have a healthy pregnancy and a healthy child," he said.
The report was released online May 20 in the Journal of Clinical Endocrinology & Metabolism.
Dr. Alan Copperman, director of the division of reproductive endocrinology and infertility at Mount Sinai Hospital in New York City, said, "People who are trying to get pregnant should optimize their health."
This includes not smoking, exercising, eating a healthy diet and maintaining a healthy weight. Whether cholesterol by itself affects fertility isn't clear, Copperman said.
"We are nowhere near establishing a direct correlation between cholesterol and the ability to get pregnant," Copperman said. "I don't think taking medication or changing your diet will immediately improve your fertility."
For the study, Schisterman and colleagues collected data on 501 couples who were trying to have a baby. These couples took part in the Longitudinal Investigation of Fertility and the Environment (LIFE) study, which was designed to examine the relationship between fertility and exposure to environmental chemicals and lifestyle.
At the start of the study, the researchers measured each couple's cholesterol levels. The investigators found that couples took significantly longer to become pregnant when both partners or the woman had high cholesterol levels.
Among the couples, 347 conceived over the year of the study. Fifty-four couples didn't conceive. One hundred couples withdrew from the study, including some whose plans to have a child changed.
For more about infertility, visit the U.S. National Library of Medicine.