I'm pregnant. Do I need a multivitamin?

Raising a healthy baby requires getting enough nutrients during pregnancy.

However, instead of following a healthy diet to get these nutrients, many people rely on "pink" multivitamins.

These supplements are widely advertised for pregnant or breastfeeding women, as well as those planning to become pregnant. They contain folic acid, iodine, iron, vitamin D, vitamin B12, calcium and many other vitamins and minerals.

Multivitamins during pregnancy are, in most cases, a waste of money. At worst, there is a risk that they could harm you and your baby.

Most people only need folic acid and iodine.

Official dietary guidelines recommend taking only two supplements before and during pregnancy: folic acid (folate) and iodine.

It is recommended to take a folic acid supplement one month before conception and during the first three months of pregnancy. The recommended dose is 400 micrograms per day to reduce the risk of neural tube defects (such as spina bifida) in newborns. Folate needs remain high throughout pregnancy, and some people may be prescribed higher doses of folic acid or other forms of folate depending on their individual medical needs.

Due to mild iodine deficiency in Australia, people who are pregnant, breastfeeding or planning to become pregnant should also take an iodine supplement of 150 micrograms per day to support the baby's brain development. People with thyroid disease should consult a doctor first.

However, in individual cases, other nutrients may be needed during pregnancy. For example, vegetarians or vegans may need to take vitamin B12 and iron supplements on the advice of their doctor. People diagnosed with vitamin D or iron deficiency will be prescribed supplements to increase their levels. Those at risk for certain conditions, such as preeclampsia, may need to take a calcium supplement from mid-pregnancy.

So why are multivitamins so popular?

Multivitamins are promoted as an essential part of pregnancy, and obstetricians often prescribe them.

In Australia, more than 4 in 5 people take a multivitamin during pregnancy. People see it as "insurance" to ensure they get enough nutrients.

Our study, using data from the Queensland Pregnancy Cohort, shows that socioeconomic factors influence the likelihood of using multivitamins during pregnancy. We found that those with access to private obstetric care and health insurance, and those who ate more meat (all associated with having more money) were more likely to use multivitamins.

This is not surprising given the high cost. The most popular prenatal multivitamin costs at least A$180 for use in the month before conception and throughout pregnancy. Compare that to less than A$40 for a supplement containing only folic acid and iodine for the same period.

Expensive brands are no better. The price is largely determined by the public perception of the brand's quality, which is shaped by strong marketing. For most vitamins, any excess is excreted through urine, turning it into, at best, expensive pee.

What happens if you have too much?

Our study found a very high reliance on supplements, especially for folic acid, iron and iodine, to meet nutrient needs.

If people's diets already provide enough of these nutrients and supplements provide additional amounts, there is a risk of nutrient overload.

For example, more than 1 in 20 people in our study had high folate intakes (above the safe " upper intake level "). Nearly half of all study participants exceeded the upper intake level for iron. Nearly all of them took multivitamins and had higher-than-normal blood levels of these nutrients.

Folic acid intakes above the upper intake level have been associated with lower birth height in children, decreased cognitive development in children, and an increased risk of developing asthma in childhood. Taking folic acid at the recommended daily dose of 400 micrograms after the first trimester, however, may be beneficial for a child's cognitive development, although further research is needed before this can be routinely recommended.

High doses of iron increase the risk of high red blood cell count in the expectant mother. This condition increases the risk of pregnancy complications, including small for gestational age, stillbirth, gestational diabetes, preeclampsia, and low birth weight.

When it comes to iodine, about one in four expectant mothers taking multivitamins in our study had very high intake levels, which is associated with poorer neurodevelopmental outcomes in children.

Chances are you're getting enough nutrients.

In low- and middle-income countries, multivitamins have a place; they improve weight gain during pregnancy, birth weight, and may reduce the risk of preterm birth.

In high-income countries like Australia, the diet is extremely diverse. There are also mandatory food fortification programs – folic acid and iodized salt have been used in bread since 2009.

In these countries, frequent use of multivitamins may pose health risks to the mother and fetus. This includes the development of gestational diabetes (possibly due to high iron intake ) and autism in children.

However, there are people who do not take any supplements during pregnancy. Our study, which looked at supplement use around 28 weeks of pregnancy, found that those under 30 and those with lower household incomes were the least likely to take supplements. These same groups also tend to have poorer diets.

What should I take?

People should look for supplements that contain only folic acid and iodine at the recommended dose, or take them as separate supplements.

They should work closely with their midwives and possibly an accredited dietitian to focus on getting enough from each of the five food groups.

Supplements should not replace a healthy diet. There are many benefits to eating a variety of foods that contain many additional nutrients and other compounds that we cannot get from supplements. Following dietary recommendations can also save you money.

Healthcare professionals also need to stop routinely recommending these expensive "pink" multivitamins and instead focus on encouraging people to eat healthier. Other than folic acid and iodine, supplements should only be prescribed according to individual needs. Multivitamins are not a must for everyone during pregnancy.

The results of the work are described in detail in an article published in The Conversation journal.