Want babies? Eating ice cream and drinking whole-fat milk may help, a new study suggests.

Women who consume at least one daily serving of high-fat dairy reduce the risk of infertility caused by lack of ovulation by more than a quarter compared with those who eat one such portion a week, Harvard University researchers found.

The study also found the more low-fat dairy women had, the less likely they were to ovulate. Those who had at least two servings of low-fat dairy a day faced an 85% increase in the risk of infertility compared with those consuming less than one serving a week, according to the research, which was published in the journal Human Reproduction yesterday.

“What we think at this moment is that either dairy fat itself or something traveling along dairy fat, such as cow’s sex hormones present in milk, may explain the association,” Jorge Chavarro, the lead researcher, said in an e-mail exchange. Mr. Chavarro and his colleagues estimate 10% to 15% of couples trying to conceive encounter some fertility problems, and a lack of ovulation is a cause in a quarter of those cases.

Clarifying the role of dairy intake in fertility is important as the American government advises women to eat two or three daily servings of low-fat dairy. The link between low-fat dairy and ovulation requires more research to confirm the findings, said Mr. Chavarro, who works at the nutrition department of Harvard’s School of Public Health.

Current dietary guidelines “may be deleterious for women planning to become pregnant,” according to Mr. Chavarro.

The researchers studied 18,555 women aged 24 to 42 who tried to become pregnant between 1991 and 1999. Every two years, the women were asked if they had tried to conceive, and if they had been unable to for more than a year they were asked why. They also supplied information on what they drank and ate. Some 438 women reported infertility because of failure to ovulate.

The condition, known as anovulatory infertility, occurs when the ovaries don’t produce an egg. It can be caused by diet, eating disorders, excessive exercise, or cysts. Long-term use of the contraceptive pill is also a possible reason.

Previous studies suggested lactose might be associated with this type of infertility, but Mr. Chavarro found “neither a positive nor a negative association.” No link was found with calcium, phosphorous, or vitamin D intake either, he said.

Analysis of the foods consumed showed that the more ice cream the women ate, the lower the risk of this kind of infertility. Those enjoying at least two portions of ice cream a week had a 38% lower risk compared with women consuming ice cream less than once a week, the study showed.