But increasingly, there is a new concern.
It is estimated about half of Australian women are entering pregnancy overweight or obese, with many putting on excessive weight while pregnant.
Jane Raymond, manager of Maternity and Newborn in NSW Health, said weight gain tends to be cumulative and lasting during child-bearing years..
"Pregnancy now is called an independent risk factor for obesity," Ms Raymond said.
Increasingly, research is linking a pregnant mum's weight to the health of her child.
Basically, if a mother is overweight or obese, her children are more likely to be heavy as well. And this can be bad news for both of them.
Overweight women have a multitude of health issues during pregnancy, such as increased risk of caesarean birth, gestational diabetes, high blood pressure and foetal macrosomia, which is when a baby is born weighing more than four kilograms.
The US Institute of Medicine recommends women have a normal weight gain between 11.5 and 16 kilograms.
Obese women should gain no more than nine kilograms.
"We have relatively good evidence that if women gain within these recommendations, they will have the healthiest pregnancy for their weight," Ms Raymond said.
'Too little, too late' to intervene in pregnancy: experts
One solution is to offer women more support while pregnant, to watch how much weight they are gaining. That has had mixed results.
One program run out of St George Hospital in Sydney's south diverts overweight or obese mums-to-be to attend group antenatal classes, as well as their midwife.
The classes cover a range of topics, from healthy eating to natural childbirth.
Jane Raymond said women in the program follow Australian dietary guidelines rigorously.
Mothers-to-be are also weighed at each antenatal appointment to make sure they meet their weight target.
Researchers found some of the women gained less than the recommended amount of weight.
But half of the women in the program gained more weight than recommended by the Institute of Medicine guidelines.
Associate Prof Kirsten Black, joint head of obstetrics, gynaecology and neonatology at the University of Sydney, said intervening before pregnancy was preferable.
"Once they are already pregnant, it's too little, too late and you really need to make the changes to wait before pregnancy if you are going to potentially see better outcomes," Associate Professor Black said.
"Essentially, it would be to see women before they conceive to identify any health or family medical history, to provide them with information about dietary and lifestyle changes, about the need for vitamin supplementation."
And partners are not off the hook.
"Obviously [we] would see them with their partners as well because increasingly it is likely that the father's health and weight could potentially impact on the health of the baby as well," she said.
Hear more of RN Health Report's International Women's Day special.