An Australian study has found just over a quarter of women took the correct amounts of folic acid and iodine supplements during pregnancy.

A majority of Australian women aren't taking the recommended dosage of folic acid and iodine supplements during pregnancy, a new study has found.

The study of more than 850 women found that around 90 per cent knew that folic acid should be taken to help their unborn babies, but only 27 per cent ended up taking the correct dosage, or even knew how much they needed.

Knowledge of iodine requirements was a bit lower at 56-69 per cent. Just 23 per cent knew about the correct dosage.

Folic acid is a B group vitamin that helps prevent neural tube defects, such as spina bifida in infants.

Iodine is nutrient needed for the development and functioning of the thyroid gland, brain and nervous system, especially in infants and young children.

According to a report released by the Australian Institute of Health and Welfare (AIHW) earlier this year, the rates of spina bifida and other neural birth defects in Australian babies have significantly decreased since the fortification of bread was made compulsory.

Mandatory fortification of bread with folic acid and iodine was introduced in Australia in 2009 under the Australia New Zealand Food Standards Code.

A review of the bread fortification program, conducted by the AIHW, found the overall rate of neural tube defects (NTDs) had decreased by 14.4 per cent since its implementation.

There was an even bigger decrease of NTDs among babies born to teenagers and Aboriginal and Torres Strait Islander women.

The rate of NTDs among teenagers decreased by almost 55 per cent, and by 74 per cent among Aboriginal women.

Despite this, the authors of The University of Adelaide study, published in the Australian and New Zealand Journal of Public Health, say new strategies to increase the adoption of preconception iodine supplements must be explored "particularly given that a large percentage of pregnancies are unplanned."

They also want to see GPs play a bigger part in enforcing the uptake of the supplements.