A new study from Princeton University finds that children conceived during the month of May face a 10 percent increase in risk of being born prematurely compared to babies conceived at other times of the year. The reason? Flu viruses.
Expectant mothers have increased exposure to the seasonal flu during January and February, exactly when a baby conceived in May would be nearing term.
“We were surprised that the relationship between potential flu exposure and premature birth appears to be so evident in the data,” said study author Janet Currie, director of the Center for Health and Wellbeing at the Woodrow Wilson School at Princeton University. “There has been some recent work suggesting that flu can induce premature labor in women late in pregnancy, and our results appear to corroborate this.”
Currie, who conducted the study with researcher Hannes Schwandt, added that if pregnant women got flu shots, they might not be at risk of premature labor due to flu infection.
Another interesting finding: babies conceived during the summer months tended to weigh slightly more at birth than babies conceived at other times of the year.
“The birth weight results suggest that infants conceived during the summer have higher birth weight in part because mothers tend to gain more weight during pregnancy when they conceive in summer,” Currie said. “It seems likely that this is because they have a better diet, though we cannot directly observe that in our data.
“We cannot rule out other factors that might also be important for pregnancy outcomes,” she said. “But we think the message of our paper is that parents should take steps to guard against known problems,” suggesting that the most practical thing pregnant women can do is simply eat well and get a seasonal flu shot. “That would probably be a more sensible approach then trying to time conception to avoid May.”
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