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 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.

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.