Olga Yakusheva, an associate professor at University of Michigan in the US began investigating weight comparisons between women with and without children.
In a study of nearly 30,000 women who had given birth between one and four times, researchers found that most women never returned to their pre-pregnancy body weight after birth.
However, their weight at 1-2 years after giving birth was nearly identical to what they could have been expected to weigh had they remained childless.
The typical age-related weight gain for women is 1.94 pounds a year. The researchers found women with toddlers gained almost a full additional pound annually.
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The reason many mothers have higher rates of weight gain is due to lifestyle, said Yakusheva.
"Mothers tend to put the needs of their children first so they might not be exercising or taking care of themselves," she said.
"It might also be little things like finishing the food on their child's plate or spending more time sitting with their kids reading or watching a movie," she added.
"But it is much better to take a holistic approach focused on a long-term healthy lifestyle before, during, and after pregnancy," she said.
She also strongly emphasises that these findings should not make mothers feel guilty.
"Understanding the demands of motherhood and age-related weight gain is important for promoting positive expectations of body image after pregnancy. As long as women are healthy, that is what matters," she stated.
Researchers encourage health care providers to counsel women about weight changes expected with age, and to make them aware of subtle ways parenthood could exacerbate the ageing-related weight gain trend over many years.