Medical experts are calling for a national strategy to help young women maintain a healthy weight before conceiving a baby, with research showing the obesity epidemic is causing "substantial" health problems for mother and child.
A study published in the Medical Journal of Australia found there's been a big increase in the number of overweight and obese first-time mums.
Researchers analysed the data for more than 42,000 first-time mothers who gave birth to a single child at the Royal Prince Alfred Hospital in Sydney between January 1990 and December 2014.
Over the 25 year period, the prevalence of mothers who were classified overweight according to their body mass index (BMI) increased from 12.7 per cent to 16.4 per cent. BMI determines whether you are in a healthy weight range for your height.
The prevalence of obesity rose from 4.8 per cent to 7.3 per cent, while the proportion of women with a 'normal' weight range fell from 73.5 per cent to 68.2 per cent.
For almost one in four (23.8 per cent) pregnant women who had pre-eclampsia between 2010-14, the condition was attributable to carrying too much weight.
Being overweight or obese was associated with 17 per cent of gestational diabetes cases and 23.4 per cent of fetal macrosomia (a baby weighing more than four kilograms).
However a "wide range" of these complications could have been averted if these women had lost enough weight to drop one BMI (body mass index) category, says co-author Associate Professor Associate Professor Kirsten Black, Joint Head of Discipline of Obstetrics, Gynaecology and Neonatology at the University of Sydney.
"We could prevent around 19 per cent of pre-eclampsia cases, 15.9 per cent of macrosomia, 14.2 per cent of gestational diabetes and about 8.5 per cent of caesarean sections," Professor Black said.
Nearly six per cent of babies born premature could have been prevented, she added.
The authors have called for a greater investment in obesity prevention strategies that target women prior to starting a family.
Professor Black says a growing body of evidence in epigenetics - the study of heritable changes in gene function that do not involve changes in the DNA sequence - shows this is critical to ensuring the health of future generations.
"At the time of conception, the health and lifestyle of parents, including diet, body weight and smoking, impacts not only on the developing foetus but also on the long term health outcomes of that child," Professor Black said.
"The World Health Organisation, looking at trying to end childhood obesity, lists pre-conception care as one of the six key strategies because it's vital that the mother's weight is as normal as possible around the time of conception because it will have implications not only for weight but also for metabolic disease in the child and cardiovascular disease potentially in the future," she said.
