ATLANTA (CBS Atlanta)– Being the oldest woman in a chain of siblings may be linked to heavier weight, according to new research.

A new study suggests that firstborn women are more likely to be overweight or obese as adults when compared to their younger sisters, as reported by CBS News.

Researchers from New Zealand evaluated birth data including information from 99 percent of all births in Sweden since 1973. The study focused on births between 1991 and 2009, while analyzing data from women who were at least 18 at the time of their first pregnancy and who had been born to a mother at least 18 years old. About 29,000 women were analyzed, including 13,406 pairs of sisters. Weight, height and information regarding current health, lifestyle, and family history were all factored into the findings.

Although firstborn girls were slightly lighter than their second-born sisters at birth, as adults who were expecting children themselves, firstborn women had a 2.4 percent higher body mass index (BMI) than their second-born sisters, according to the study. These women were also more likely to be overweight and obese.

Researchers note that no definitive conclusions can be drawn from the study and that the reasons behind certain health risks for firstborn women is still unclear.

CDC data shows that more than one-third (35.1 percent) of U.S. adults over the age of 20 are considered obese. And 69 percent of American adults over the age of 20 are either overweight or obese.

Lead study author Professor Wayne Cutfield says that a change in blood supply to the placenta between pregnancies could affect nutrient supply, possibly reprogramming the regulation of fat and glucose in children. Other experts suggest that environmental factors are most likely a big factor.

“In many cultures, moms are more meticulous with their firstborns,” Dr. Maria Peña, Director of the Center for Weight Management at Lenox Hill Hospital in New York City told CBS News. “With the very firstborn, everyone’s helping out and over-feeding the baby, making sure it’s at a ‘healthy weight.’ But with second children, parents know what to expect and they’re not so overprotective so maybe they feed them a little less.”

Pena says these eating habits could follow individuals throughout their lives, with people developing obesity later in life often having issues regarding signals in their brain telling them to stop eating.

Further research involving more diverse populations, women of different races, education levels, and socioeconimic background could shed light on strengthening the findings.


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