The study published today (Friday 4 May) in Human Reproduction, one of the world's leading reproductive medicine journals, asked 5598 women in Australia, New Zealand, the United Kingdom and Ireland about their diet.
Women who ate fast food four or more times a week took almost a month longer to get pregnant than women who never or rarely ate this type of food.
Among all the couples in the study, 468 (8 percent) couples were classified as infertile (defined as taking longer than a year to conceive) and 2204 (39 percent) conceived within a month.
First author Dr Jessica Grieger, post-doctoral research fellow at the University of Adelaide, said: "We recommend that women who want to become pregnant should align their dietary intakes towards national dietary recommendations for pregnancy".
Researchers found that eating fast food regularly was linked to a twofold increase in the risk of infertility in women of childbearing age.
A new study in the journal Human Reproduction found women who eat fast food may have difficulty getting pregnant.
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Midwives obtained information regarding the participants diet and how long it took them to get pregnant as part of their initial antenatal visit at approximately 14-16 weeks' gestation.
But the study did not prove a cause-and-effect relationship between food and fertility; it only showed an association.
To help fill that gap, Roberts and a dozen colleagues in Australia, Britain and New Zealand combed through data gathered through questionnaires by midwives between 2004 and 2011 in all three countries for the Screening for Pregnancy Endpoints (SCOPE) survey.
A total of 5,600 women in the early stages of pregnancy focused on their diet in the months before conception. The list was detailed and included fresh fruit, leafy green vegetables, specific types of fish, burgers, fried chicken, tacos, pizza and fries. The study didn't take into account fast food eaten at home, such as TV dinners.
"With one in six couples now struggling to conceive, many couples are now asking what they can do to optimise their fertility", said fertility dietitian Melanie McGrice at St Vincent's Hospital in Melbourne.
"I think having male fertility, male alcohol intake, male habits, like tobacco or marijuana or other chemical exposures - that can clear up some of the confounding factors, too", Dr. Chang says. A major strength is the large group of women included in the study. Grieger said, "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.