Researchers at the University of Adelaide's Robinson Research Institute asked 5598 women in Australia, New Zealand, the United Kingdom and Ireland about their diet to learn its effect on their pregnancies.
Women who eat a lot of fast food and little or no fruit may take longer to get pregnant, the results of a new global study involving Irish women indicate. And while eating fruit and fast foods appeared to affect how long it took a woman to get pregnant, eating vegetables and fish did not appear to make a difference.
Eight percent of the couples in the study were classified as infertile, defined as taking longer than a year to conceive, while 39 percent conceived within a month.
"We recommend that women who want to become pregnant should align their dietary intakes toward national dietary recommendations for pregnancy", said lead author Jessica Grieger, a researchers at the University of Adelaide.
On an extreme level, however, too much of fast food compared to none at all increased the risk of not becoming pregnant by 41%.
The researchers found that compared to women who ate three or more portions of fruit in the month before conception, those who ate fruit less than one to three times a month took around two weeks longer to become pregnant. The impact of maternal diet before conception among women more generally has received scant scientific attention.
Information about the time it had taken to get pregnant, along with the women's diets in the month before conception, was collected.
"Healthier foods or dietary patterns have been associated with improved fertility, however, these studies focused on women already diagnosed with or receiving treatments for infertility, rather than in the general population", the researchers wrote. The list was detailed and included fresh fruit, leafy green vegetables, specific types of fish, burgers, fried chicken, tacos, pizza and fries. Junk food consumed that originated from supermarkets was omitted from the analysis, which is considered an oversight in the study. We adjusted the relationships with pre-pregnancy diet to take account of several factors known to increase the risk of infertility, including elevated body mass index [BMI] and maternal age, smoking and alcohol intake.
Detailed answers given by almost 5600 women in the early phase of pregnancy focused on what they ate in the months preceeding conception.
"They did not have information on the partners, which I think would have also been good information because obviously diet can impact sperm", says Lynn Westphal, MD, director of fertility preservation and third party reproduction at Stanford Children's Health in California, who was not involved in the study. A major strength is the large group of women included in the study.
For any dietary intake assessment, one needs to use some caution regarding whether participant recall is an accurate reflection of dietary intake.
The findings also suggest that these women are less likely to conceive within one year.
However, doctors have also said before that a good diet can improve the chances of pregnancy.