Researchers at the University of Sydney examined more than 40,000 pregnant women over a 25-year period and found the prevalence of overweight and obese first-time mothers had increased and the number of women within a normal body mass index (BMI) range had fallen.
At the same time, the proportion of poor health outcomes attributable to excessive weight during pregnancy had steadily increased.
“This includes maternal complications such as pre-eclampsia, gestational diabetes and caesarean birth, as well as complications for the baby, including being large for gestational age,” said senior author Kirsten Black.
Associate Professor Black said previous efforts to reduce the risks of maternal obesity in pregnant women had failed, and that obesity prevention strategies needed to target women prior to getting pregnant.
“The sentiment from nutritionists and obstetricians is that the greatest impact on adverse outcomes will occur if women lose weight before they get pregnant,” she said.
Dropping one weight class would improve health outcomes
Researchers analysed the BMIs, demographic characteristics and health outcomes around the time of birth of 42,582 first-time mothers at Sydney’s Royal Prince Alfred Hospital between 1990 and 2014.
“We were interested in looking at how the trends had changed over time in obesity, and to what extent that was impacting on a range of adverse health outcomes,” Associate Professor Black said.
“As a consequence of that, we saw a rise in a whole range of adverse outcomes such as caesarean sections, prematurity, gestational diabetes, stillbirths, foetal abnormality, pre-eclampsia and foetal macrosomia [larger than average baby],” Associate Professor Black said.
A substantial number of those outcomes could have been avoided with obesity prevention strategies that reduce pre-pregnancy weight, she said.
“Were overweight and obese women to have moved down one BMI category during 2010 to 2014, 19 per cent of pre-eclampsia, 15.9 per cent of foetal macrosomia, 14.2 per cent of gestational diabetes, and 8.5 per cent of caesarean deliveries … could have been averted,” the authors wrote.
Pre-conception health is key
Once women are already pregnant it may be too late to reduce the risks of maternal obesity, Associate Professor Black said.
“There have been a number of studies that have tried to alter the impact of obesity on adverse outcomes in women who are already pregnant, so instituting things like exercise and dietary changes,” she said.
“But the results have been disappointing in all those trials… so it’s important women optimise their health before pregnancy.”
In addition to population-wide strategies to reduce obesity, the gynaecologist said health professionals needed to get better at having “healthy conversations” with people about their weight.
“There are a range of conditions for which women should be advised on around pregnancy … so we need to also ensure that there is greater access to pre-conception care.”