The season in which a baby is born may influence the baby's birth weight as well as how quickly the baby gains weight during the first four months of life. A study published in the May issue of the Journal of Nutrition found significant differences among U.S. ethnic groups, with lower birth weights and lower rates of weight gain for black infants born in autumn, compared to other seasons.
"To our knowledge, this is the first description of seasonal variation in infant weight gain in a western society. Previous studies have focused on birth weight or on infant growth in low-income countries where food intake is directly linked to agriculture and the seasons," said Nicolas Stettler, M.D., a pediatric specialist at The Children's Hospital of Philadelphia, and a co-author of this study.
This research could be important because patterns of weight gain in early infancy may predict obesity, diabetes, and other cardiovascular health problems in adolescence and adulthood. Previous research by Dr. Stettler showed that rapid early infancy weight gain - even an extra 100 grams per month, a modest increase over the normal growth weight gain pattern - increased the risk of being overweight at age seven by more than 25 percent. "We continue to try to understand the effects of birth weight and postnatal weight gain on long-term health," said Stettler.
Researchers from The Children's Hospital of Philadelphia; Trinity College, Dublin Ireland; and St. George's Medical School, London studied a multiethnic sample of 24,325 infants who were born at full term gestation at 12 sites throughout the U.S. between 1959 and 1965.
Black infants born in the summer and fall had significantly lower birth weights than those born in the winter and spring. Additionally, weight gain for black and Puerto Rican infants during the first four months of life was significantly lower for those born during the fall compared to those born in the spring and summer. This was not observed in white infants.
"A possible reason for the variation between ethnic groups could be related to health care access. Higher levels of prenatal and infant care among whites during this era may have evened out seasonal differences in that group, " said Dr. Stettler. "This study further emphasizes the importance of appropriate prenatal and postnatal care for all infants."
The seasons were defined as winter (December, January, February), spring (March, April, May), summer (June, July, August), and fall (September, October, November).
The researchers say that further study is necessary, but that when looking at the association between early growth and adult health, researchers should pay attention to the birth season and early infancy growth.