Mother’s Age Linked to Newborn’s Birth Weight
By Lynne Peeples, from Reuters Health Information
NEW YORK (Reuters Health) – Older women are more likely to give birth to bigger babies, while smaller newborns are more common among younger moms, Dutch researchers say.
Prior studies have hinted at links between a mother’s age and her baby’s birth weight, as well as potential health consequences when babies are very small or very large. Babies who grow less than expected in utero have a higher risk of birth complications, as well as diabetes and heart disease in adulthood. Very large newborns may be more likely to become obese later in life.
This could be particularly relevant as the age at which women are having children is still increasing in the Western world. For example, according to a 2010 study by the Pew Research Center, the percentage of U.S. babies being born to women older than 35 went from 9 percent in 1990 to 14 percent in 2008.
Researcher Rachel Bakker of the Erasmus Medical Center in Rotterdam, the Netherlands and her colleagues studied 8,568 Dutch women who gave birth between 2002 and 2006.
The average newborn weighed around 7.7 pounds (3,500 grams). The researchers defined a “small” baby as one weighing 5.5 pounds (2,500 grams) or less and a “large” baby as weighing 10 pounds (4,500 grams) or more.
In total, about 5% of newborns were small, and another 5% were large.
Compared to 30-to-35-year-olds, mothers under 25 tended to be more likely to have small babies. For example, about 4% of 30-to-35-year-olds had small newborns, compared to 7% of mothers under 20.
On the other hand, older mothers were more likely to have large babies, the researchers reported online January 18th in the British Journal of Obstetrics and Gynecology. The risk of a large baby went from 3% in the very youngest women, to about 6% in 30-to-35-year-olds, to roughly 10% in women over 40.
For the very youngest mothers, the link between age and the risk of delivering a small baby was mostly due to sociodemographic and lifestyle factors. In the other age groups, sociodemographic factors- but not lifestyle factors – could also explain why younger women tended to have smaller babies.
But none of those factors could explain why the risk of having a large baby went up in the oldest women. The findings suggest that other factors in women’s bodies could be playing a role, but the researchers don’t know yet what those might be.
Bakker noted that there might be other nonbiologic factors involved that were not accounted for in the study, and that more research is needed to clarify the range of potential effects.
In the meantime, she told Reuters Health by email, there isn’t enough information available “to advise women about the most optimal age to have children.”