The chance of having a premature baby is almost four times lower if the mother eats fish once a week, according to a new study.
Having fish on the menu also reduces the likelihood of low birth weight, according to the research.
The Maternal Nutrition Group within the Danish Epidemiology Science Centre in Copenhagen surveyed more than 8,700 pregnant women about how much fish they ate during their pregnancies.
It publishes its findings this morning in the British Medical Journal.
The occurrence of preterm births fell from 7.1 per cent in women never eating fish to just 1.9 per cent in those eating fish at least once a week.
This means the chance of having a preterm infant was about 3.7 times lower for women who ate fish each week.
The researchers, led by Dr Sjurour Frooi Olsen, senior scientist at the Epidemiology Centre, found that low birth weight and premature birth rate both tended to decrease with increasing fish consumption.
Average birth weight and length of gestation increased as fish consumption increased.
The effective fish "dose" rate for the women studied ranged from none to 15g of fish per day with the women eating at least 15g per day reaching the maximum benefit in terms of lower risk of a preterm baby.
The researchers found that this new study matched well with related studies of women who took fish oil supplements during pregnancy.
"Overall, the findings agree with the randomised trials showing that consumption of fish oil in pregnancy can increase birth weight by prolonging gestation and reduce the risk of recurrence of preterm delivery," the authors write.
The study made adjustments "confounding" factors such as women who smoked, pregnancy during teenage years, educational and cohabitant status and their own weight and height.
"The association between intake of fish and risk of foetal growth retardation weakened but was not always fully abolished after adjustment for potential confounding," the authors say.
