In a study, researchers from New Zealand have suggested that birth order may have an impact on the weight of a woman, with the firstborn women being slightly more overweight or obese as adults, CBS News reports.

The researchers analyzed data from the Swedish Birth Register, focusing on the time period between 1991 and 2009. They analyzed data on 13,406 pairs of sisters, a total of around 29,000 women.

The study suggested that firstborn girls were born slightly lighter than their second-born sisters, but when they grew up and were expecting children themselves, they had a 2.4 percent higher body mass index than their sisters. The firstborns were more likely to be overweight and obese than the second born.

Similar studies on men have suggested that firstborn men are at a higher risk of diabetes and high blood pressure.

However, the researchers said that the study provides no definitive conclusions.

Dr. Maria Peña, Director of the Center for Weight Management at Lenox Hill Hospital in New York City, told CBS News that environmental factors could also play a role.

"In many cultures, moms are more meticulous with their firstborns. 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," she said. "People that develop obesity later on in life forget to listen to the signal in their brain that tells them to stop eating. Early on in life, some kids are taught to override that signal. If a parent tells a child to keep eating even when they're not hungry, then that's a habit they learn."