Pregnancy may not be the best time for obese mothers-to-be to shed extra kilograms after research finds it is usually "too little, too late" for any meaningful benefit.
Evidence is mounting that obesity should be tackled before pregnancy, and that goes for men and women who want to become parents.
About half of Australian women are overweight or obese when they get pregnant and that can lead to an increased risk of gestational diabetes, hypertension and pre-eclampsia.
Other adverse consequences include an increased chance of a caesarean delivery, stillbirth or miscarriage, while babies born to overweight or obese parents are at greater risk of childhood obesity.
If trends persist, about 80 per cent of Australian adults and a third of Australian children will be overweight or obese by 2025, according to a Perspective piece published in the Medical Journal of Australia on Monday.
Written by associate professor Kirsten Black and Adrienne Gordon from the University of Sydney and Royal Prince Alfred Hospital, the article said pregnancy might not be the ideal time to try to reduce the effects of obesity.
"There's been a number of trials that have tried to reduce the problems associated with obesity by intervening in pregnancy," Professor Black said.
"But these trials, there's two big studies in particular, have had very limited success in reducing the adverse outcomes that we want to reduce, such as very large babies, increased risk of complications such as diabetes and caesarean section rates.
"Evidence from animal studies is indicating that perhaps we need to intervene before women get pregnant."
The weight of both parents when a baby was conceived could have long-term implications for the child, Professor Black said.
"We need to probably target women – and men – of reproductive age before they actually get pregnant," she said.
"Women and men should be supported to seek advice from their GP, because, apart from the complications in pregnancy, there's increased risk of obesity in their children if women are obese at the time of conception.
"There's also long-term health consequences into adulthood for those children."
Dr Gordon and Professor Black have applied for funding to study pre-conception care for women planning a pregnancy.
"Pre-conception care involves providing health care to women of reproductive ages and their partners that optimises their physical, social and emotional wellbeing prior to conception with the aim of improving health-related outcomes for women and their children," the authors wrote.
"A pragmatic approach may be to start with programs that enhance a women's knowledge of the consequences of obesity during pregnancy and the post-partum period and to inform women about post-natal programs that can reduce the risk of post-partum weight retention, and therefore obesity during subsequent pregnancies.
"The most effective interventions include both dietary and exercise components."
But such an approach required hospitals and health services to take a longer term view of pregnancy and the post-partum period, as well as government investment.