A survey has found 38 per cent of women gain too much weight during pregnancy.
On the other hand, the Queensland University of Technology survey of 664 women also showed that another 26 per cent struggled to gain enough weight, with some mothers recording a lower weight just before giving birth than they did before falling pregnant.
Being overweight or obese can lead to health complications, including gestational diabetes, while being underweight carries a different set of risks, including premature birth or having a low-birth-weight infant.
The study, published in the Australian and New Zealand Journal of Obstetrics and Gynaecology, also revealed that 56 per cent of women who were overweight before falling pregnant gained too much maternity weight, compared to only a third of their trimmer counterparts.
Researcher Susie de Jersey says two-thirds of Australian mums-to-be are in the dark when it comes to how much weight they should gain during pregnancy.
"Most women said they also didn't know the recommended amount of weight they should gain during pregnancy and reported very limited advice about healthy weight gain," de Jersey said in a statement issued by QUT.
Ms de Jersey said less than half of the study's participants viewed exercise during pregnancy as very important, possibly owing to old beliefs that physical activity was not safe for mothers-to-be, despite the opposite being widely proven.
To find out the optimum weight gain for you in pregnancy, speak to your doctor or obstetrician.