(HealthDay is the new name for HealthScoutNews.)MONDAY, June 9, 2003 (HealthDayNews) -- New research suggests that the season of birth -- and, by extension, the season of conception -- could affect the weight of black newborns and young babies.
Babies born in the fall appear to be most likely to weigh less in the early months of life, potentially setting them up for cardiovascular problems when they become adults.
Researchers aren't sure why season of birth and weight appears to be connected in black babies and -- in the first few months of life -- in Puerto Ricans. "I don't think anyone knows exactly what happens," says study co-author Dr. Nicolas Stettler, a pediatric nutrition specialist at The Children's Hospital of Philadelphia.
Researchers in Philadelphia, Ireland and Great Britain studied 24,325 infants who were born in the United States between 1959 and 1965. None of the babies was premature.
The researchers report their findings in the May issue of the Journal of Nutrition.
The black babies born in the fall (defined as September-November) weighed less (an average of 6.88 pounds) than those born in the winter (6.97 pounds). A large number of black babies -- 11,477 -- were studied.
Other ethnic groups showed no such difference.
Both black and Puerto Rican babies born in the fall "gained weight less slowly in the first few months than those born in other seasons," Stettler says.
Black and Puerto Rican babies born in the fall gained an average of 816 and 820 grams per month, respectively, in the first four months of life, compared to blacks born in the spring (844 grams) and Puerto Ricans born in the summer (861 grams).
Researchers already knew that season of birth affects the weight of some newborns, Stettler says. The new study, however, is the first to reveal that weight in the first months of life is also affected.
It's possible the mother's metabolism or weight may vary by season and affect the baby, Stettler says. He adds that babies born in the fall may need to burn more calories in the cold of winter, causing them to be thinner, especially if they live in homes that are not well-heated.
"That may explain the difference between the African and European Americans. Perhaps the African-Americans were living in conditions where the infants were less well-protected," he says.
The season of conception may also play a role, he says. "We're looking at events that happened nine months before. Any of those periods could be critical for weight gain."
Abnormal weight at birth can spell trouble for babies when they reach adulthood, Stettler notes. Babies who are thinner than normal are more likely to suffer from heart problems as adults, while the fatter babies often become overweight.