By Amy Norton

NEW YORK: Women who closely adhere to a Mediterranean-style diet rich in vegetables, vegetable oils and fish may have a higher likelihood of becoming pregnant after infertility treatment, a new study suggests.

Researchers in the Netherlands found that among 161 couples undergoing fertility treatment at their center, women whose eating habits most closely matched the traditional Mediterranean diet were 40 percent more likely to become pregnant than those with the least Mediterranean-like diets.

The study, reported in the journal Fertility and Sterility, does not prove that the diet itself boosts the success of fertility treatment.

The study was "observational" -- where the researchers asked couples about their usual diets, separated them into groups based on their diet patterns, then followed the groups' outcomes after fertility treatment. Such studies cannot prove cause-and-effect.

However, the findings point to a possible role for diet in fertility treatment success, according to the researchers, led by Dr. Regine P.M. Steegers-Theunissen of Erasmus University Medical Center in Rotterdam.

In an email to Reuters Health, Steegers-Theunissen suggested that couples considering fertility treatment eat a balanced diet that includes healthy doses of vegetable oil, vegetables, beans and fish.

The study included 161 couples undergoing fertility treatment at the university.

Two-thirds underwent in-vitro fertilization (IVF), while the rest underwent intracytoplasmic sperm injection, or ICSI.

The latter is typically used when the man has a low sperm count or poor sperm quality. It involves isolating a single sperm from the man and injecting it into the woman's egg; if fertilization is successful, the resulting embryo is transferred to the woman's uterus.

Before treatment, the couples completed detailed questionnaires on their eating habits over the past month.

When the researchers analyzed the data, they identified two common diet patterns among the women: the Mediterranean diet, defined as high in vegetables, vegetable oils, fish and beans, but low in snack foods; and the "health-conscious" diet, which was high in fruits, vegetables, whole grains, beans and fish, and low in meat and snack foods.

The researchers found that the one-third of women who scored highest in adherence to the Mediterranean diet had a pregnancy rate of 30 percent following IVF or ICSI. The pregnancy rate was 25 percent in the one-third of women with the least Mediterranean-like eating habits.

When Steegers-Theunissen and her colleagues considered several other factors -- including the women's age, body weight, and drinking and smoking habits -- there was no relationship between the so-called health-conscious diet and rates of pregnancy.

In contrast, the group that most closely adhered to the Mediterranean diet was 40 percent more likely to become pregnant than their counterparts whose diets were farthest from the Mediterranean pattern.

The researchers did not assess pregnancy outcomes, so the diet's relationship to the ultimate success of fertility treatment is not clear. But "this is the first step," Steegers-Theunissen said.

The Mediterranean and health-conscious diets had many similarities, but there are a few potential reasons why the former might affect fertility treatment success, according to the researchers.

One is the high intake of vegetable oils in the Mediterranean diet.

The omega-6 fatty acids in these oils, the researchers note, are precursors to hormone-like substances in the body called prostaglandins. Prostaglandins, in turn, are involved in the menstrual cycle, ovulation and pregnancy maintenance.

In addition, the study found that women who most closely adhered to the Mediterranean diet had higher levels of vitamin B6 -- higher than both women whose diets were least Mediterranean-like and those who scored high on the health-conscious diet.

One study, Steegers-Theunissen and her colleagues note, found that giving vitamin B6 to women who were having difficulty getting pregnant increased their chances of conception.

Still, diet is part of a person's overall lifestyle, and the study could not account for all of the factors that could explain the connection between the Mediterranean diet and pregnancy rates.

Proving that the diet itself offers benefits would require a clinical trial where women were randomly assigned to follow either a Mediterranean diet or a comparison one.

"Unfortunately," Steegers-Theunissen said, "this will be hardly feasible."