Many factors weigh in to whether a baby is delivered at term or prematurely, from smoking to diet to genetics. Now even the time your baby is conceived can have an effect. New research published in the journal Proceedings of the National Academy of Sciences found that babies conceived in the month of May are 10 percent more likely to be born premature, and it has something to do with the flu. Flu season peaks in January and February, precisely when a baby conceived in May would be nearing term.

The study of more than 647,000 moms conducted at the Center for Health and Wellbeing at the Woodrow Wilson School at Princeton University found evidence of a link between the flu and birth time. They also found that babies conceived during the summer months tended to weigh a little more at birth than those conceived during other seasons.

The simple answer to avoid the problem of premature birth related to the flu, then, is to get a flu shot rather than plan conception around a certain season. The American College of Obstetrics and Gynecology and the Centers for Disease Control and Prevention both recommend the shot, which is safe for expectant moms. Coming down with the flu, on the other hand, puts pregnant women and babies at a severe risk for complications.

Why does the flu pose such a hazard for moms-to-be and their buns-in-the-oven? Influenza is a respiratory illness caused by influenza A or B viruses. It’s highly contagious. Infants, the elderly and people with chronic illnesses or impaired immune systems — such as pregnant women — are more sensitive to infection.

Besides steeling yourself with a shot, bolster your immune system with sufficient sleep, regular exercise, stress management and standard handwashing. With a solid immune system, you can keep the flu at bay.