The physiology of pregnancy is a beautiful design but when mums gain too much weight it exposes their unborn child to diseases later in life, experts say.
Research shows that a child is at greater risk of being overweight or obese later in life if their mum carried too much weight during pregnancy.
It puts the child at greater risk of disease, with obesity linked to 11 cancers, cardiovascular disease and type 2 diabetes.
Professor Karen Sliwa, president-elect of the World Heart Federation, believes the fight against obesity must start with mums.
"If you really want to make a big impact you have to start with the pregnant mother," Prof Sliwa told AAP.
"We do know that if you eat healthy in pregnancy and you only gain your nine to 11 kilos ... your children are less likely to develop any form of diabetes or cardiovascular disease later in life than if you eat unhealthy and gain 20 kilos," she said.
Professor Sliwa was voted the first woman president of the World Heart Federation last year and is the Director of Cardiovascular Research at the Hatter Institute in Africa.
Much of her work addresses inequality in cardiovascular disease, however more recently her research in South Africa is aimed at preventing "unnecessary" weight gain during pregnancy.
Prof Sliwa says they encourage pregnant women in local communities to do simple exercises like pilates and teach them how to cook a healthy meal.
At the moment many pregnant women aren't following a healthy diet and the obesogenic diet - high in sugar and fat - is disrupting the microbiota in the gut, says Professor Emad El-Omar, Professor of Medicine at the St George and Sutherland Clinical School, UNSW.
An unhealthy microbiota - a community of millions of good and bad bacteria living in the bowel - has been linked to colon cancer, asthma, mental illness and autism.
The maternal microbiota has also been recognised as a key determinant of a range of pregnancy outcomes
An unhealthy gut during pregnancy is linked to gestational diabetes, hypertension and the potentially deadly condition pre-eclampsia.
Prof El-Omar, who is heading-up the establishment of Australia's first Microbiome Research Centre in Sydney, says during pregnancy an unexplained "shift" in the microbiota occurs between trimester one and trimester three.
This shift leads to the accumulation of fat and hence weight gain to protect the mother and foetus against "famine or poor diet".
"So it's a beautiful design," said Prof El-Omar.
But if you start pregnancy overweight or obese then the microbiota is already out of balance and this can lead to "all kinds" of negative pregnancy outcomes.
"So understanding how that imbalance occurs is key," he said.
