Pregnant women who eat a "prudent" diet rich in vegetables, fruits, whole grains and who drink water have a significantly reduced risk of preterm delivery, suggests a study published on bmj.com.
A "traditional" dietary pattern of boiled potatoes, fish and cooked vegetables was also linked to a significantly lower risk.
Although these findings cannot establish causality, they support dietary advice to pregnant women to eat a balanced diet including vegetables, fruit, whole grains, and fish and to drink water.
Preterm delivery (before 37 weeks of pregnancy) is associated with significant short and long term ill-health and accounts for almost 75% of all newborn deaths.
Evidence shows that a mother's dietary habits can directly affect her unborn child, so researchers based in Sweden, Norway and Iceland set out to examine whether a link exists between maternal diet and preterm delivery.
Using data from the Norwegian Mother and Child Cohort Study, they analysed preterm births among 66,000 women between 2002 and 2008.
To be included, participants had to be free of diabetes, have delivered a live single baby, and completed a validated food frequency questionnaire on dietary habits during the first four to five months of pregnancy.
Factors that may have affected the results (known as confounding), including a mother's age, history of preterm delivery and education were taken into account. Preterm delivery was defined as delivery between 22 and <37 weeks of pregnancy.
The researchers identified three distinct dietary patterns, interpreted as "prudent" (vegetables, fruits, oils, water as a beverage, whole grain cereals, poultry, fibre rich bread), "Western" (salty and sweet snacks, white bread, desserts, processed meat products), and "traditional" (potatoes, fish, gravy, cooked vegetables, low fat milk).
Among the 66,000 pregnant women, preterm delivery occurred in 3,505 (5.3%) cases.
After adjusting for several confounding factors, the team found that an overall "prudent" dietary pattern was associated with a significantly reduced risk of preterm delivery, especially among women having their first baby, as well as spontaneous and late preterm delivery.
They also found a significantly reduced risk of preterm delivery for the "traditional" dietary pattern. However, the "Western" dietary pattern was not independently associated with preterm delivery.
This indicates that increasing the intake of foods associated with a prudent dietary pattern is more important than totally excluding processed food, fast food, junk food, and snacks, say the authors.
They stress that a direct (causal) link cannot be drawn from the results, but say the findings suggest that "diet matters for the risk of preterm delivery, which may reassure medical practitioners that the current dietary recommendations are sound but also inspire them to pay more attention to dietary counselling."
These findings are important, as prevention of preterm delivery is of major importance in modern obstetrics. They also indicate that preterm delivery might actually be modified by maternal diet, they conclude.
In an accompanying editorial, Professor Lucilla Poston at King's College London, says healthy eating in pregnancy is always a good idea.
She points to several studies that have proposed the benefit of a diet rich in fruit and/or vegetables in prevention of premature birth, and says health professionals "would therefore be well advised to reinforce the message that pregnant women eat a healthy diet."