Firstborn women are more likely to be overweight than their younger sisters a weight study has found.
The study looked at the height and weight of 13,500 pairs of siblings born between 1999 and 2009.
Published in the Journal of Epidemiology and Community Health, the study used data from the Swedish Birth Register.
The results revealed that while first-born sisters were likely to be lighter than their younger sisters when they were born, they were more likely to be overweight or even obese in comparison to their younger siblings.
The study reads, ""Our study corroborates other large studies on men, as we showed that firstborn women have greater BMI and are more likely to be overweight or obese than their second born sisters."
Co-Author, Professor Wayne Cutfield, said that this pattern could be partly down to a change in the amount of blood the placenta receives between first and later pregnancies.
He said blood vessels could be narrower in the first pregnancy, which would reduce the nutrient supply and change how fat and glucose is regulated which would mean first born women store more fat and have less effective insulin.