Almost two-thirds of women fail to take the supplements recommended by the Ministry of Health when pregnant.
The Ministry of Health rarely recommended using supplements but did urge mothers to take additional iodine and folic acid before and during pregnancy, and iodine when breastfeeding, to help avoid neurodevelopmental problems in their babies.
University of Otago researchers carried out a study of 535 women from across the country to gauge how well the advice was followed and found only about a third of women fully adhered to the recommendations.
The iodine recommendation was followed by 52 per cent of the women while 38 per cent followed both the iodine and folic acid recommendations.
Women considering pregnancy, who were pregnant, or who were breastfeeding were recommended to take a supplement containing 150mcg of iodine each day. Iodine is important for optimal foetal and infant brain development, including their IQ later in life.
It was also recommended women take one folic acid tablet (0.8mg) each day for four weeks before conception through to 12 weeks after becoming pregnant to help prevent neural tube defects in their babies.
Associate Professor Sheila Skeaff, co-author on the paper, said although the data only captured information at one point in time it suggested low numbers of women were following the advice across the board.
"We need to make a bigger effort to promote these recommendations and increase access to iodine and folic acid supplements - we want communities to know about these nutrients, and why they are important," she said.
Skeaff said the study also found that 80 per cent of women were getting their iodine with a prescription from a GP or midwife which gave them access to a Ministry of Health subsidy.
• Iodine is essential for healthy brain development in the foetus and young child.
• A woman's iodine requirement increases substantially during pregnancy to ensure adequate supply to the foetus but most foods are relatively low in iodine content.
• Foods that are high in iodine are well cooked seafood, milk, eggs, some cereals and bread.
• The World Health Organisation has recommended the universal iodisation of salt to combat the problem.
About folic acid
• Folic acid helps the body to make new cells.
• It is important because it can help to prevent birth defects of a baby's brain and spine, such as spina bifida. Spina bifida can cause walking, bladder and bowel problems.
• Folic acid is a man-made form of a B vitamin called folate.
• The best food sources of folic acid are fortified cereals. Folate is found naturally in dark green vegetables and citrus fruits.