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.