Pregnancy is such a fascinating time of life that it’s no wonder so much speculation surrounds it. One line of thought is that a baby’s birth month brings certain characteristics for its health, almost like the signs of the zodiac are thought to influence personality. Science hasn’t been able to confirm the lore surrounding birth month but a recent Princeton University study does demonstrate a connection between spring conception and premature delivery. Seems the link is the mother’s bout with the flu during the latter stages of pregnancy.

Flu season falls between October and May in the US. Women who conceive during the spring months are in second and third trimesters when flu season arrives. Pregnant women are more prone to getting the flu than when not pregnant. Influenza during pregnancy affects the pregnancy and the baby in ways that include low birth weight and preterm birth.

To test the theoretical link between springtime conception, mom’s flu, and early delivery, researchers from the Center for Health and Wellbeing at Princeton University analyzed medical data for more than 1.4 million babies born in New Jersey, New York City, and Pennsylvania. These babies represented 647,050 groups of siblings. By studying siblings, the research team could assess fixed maternal characteristics of each mother instead of using a random sampling of individual pregnancies. They could also see seasonal contrasts in the birth outcomes of siblings born in different months to the same mother.

Seasonal differences were identified:

• Babies conceived in May were more than 10% more likely to be born early if their mother suffered the flu during pregnancy. Babies conceived in May come to term in January and February, the height of flu season in the US.
• Babies conceived during summer months were found to weight 8 to 9 grams more than babies conceived the rest of the year. This difference is thought to be linked with seasonal nutritional variations in the mother’s diet. Fresh fruits and vegetables reach peak nutritional value during the summer, perhaps translating to better-fed babies during gestation.

The findings of this study reinforce the value of flu vaccines for pregnant women. Pregnancy itself affects a woman’s immune system, heart, and lungs - all parts of the body under attack by the flu virus. The virus also contributes to increased risk of miscarriage, low birth weight, and premature delivery no matter what time of year a child is conceived. The flu shot is the best protection a woman can get for herself and her baby. A flu shot taken as soon as it’s available will provide optimum protection throughout pregnancy.

Source: Currie, J and Schwandt, H. "Within-Mother Analysis of Seasonal Patterns in Health at Birth." Princeton University Center for Health and Wellbeing. Proc Natl Acad Sci U S A. 2013 Jul 23. Web. Retrieved 7 Nov 2013.