0426 GMT November 27, 2020
The Irish study, which is the first of its kind, was carried out on nearly 10,000 mothers in the Coombe Hospital in Dublin over an eight-year period, independent.ie reported.
Researchers observed a rise in body mass index (BMI) among expectant mothers between their first and second pregnancies, with one-fifth of all women gaining weight between pregnancies.
It was found that the rate of obesity among the women rose from 11.6% in the first pregnancy to 16% in the second.
Overall, just over 10% of women became overweight by their second pregnancy, while nearly 6% developed obesity by the time they were expecting their second child.
Professor of Obstetrics and Gynaecology at the UCD Centre for Human Reproduction at the Coombe, Michael Turner, said the reasons behind the weight gain are not clear.
"The reason for the increase in BMI and obesity levels after a first baby remains uncertain. We know that it is more likely to be the case in women who are socially disadvantaged," he said.
"This leads one to suspect that women who are employed outside the home are more likely to have higher physical activity levels, or are more likely to have the resources to pay for child care while they exercise or to pay for gym membership."
Turner, along with lead author Dr. Ciara Reynolds and other colleagues, examined the records of women who attended the Coombe between 2009 and 2017.
The study found that one in five women who are in the overweight category at the start of their first pregnancy enter the obesity category by their second pregnancy.
It also found that 87% of women who are in the obesity category at the start of their first pregnancy remain in this BMI category at the start of their next pregnancy.
The development of obesity was found to be associated with formula feeding at hospital discharge, taking antidepressants or anxiolytics, postnatal depression after the first delivery, and a longer inter-pregnancy interval.
The study noted that women in professional or managerial employment are less likely to enter the obesity category the second time around.
Turner said the trends are not surprising, but it is important to have hard data on the health issue.
He said it has been found that breastfeeding does not help with shedding weight after pregnancy.
"I suspect the main culprit is reduced levels of physical activity and added sugar in processed food," he said.
"The main learning point from this study is that women should avoid putting on weight postnatally and they may need societal support to achieve this goal."