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 those who are pregnant or breastfeeding, or those planning a pregnancy. 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 advise 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 requirements 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 pregnancy should also take an iodine supplement at a dose of 150 micrograms per day to support baby's brain development. People with thyroid disease should consult their 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 at the advice of their doctor. People diagnosed with vitamin D or iron deficiency will be prescribed supplements to boost their levels. Those at risk of 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 are often prescribed by obstetricians.

In Australia, more than 4 in 5 people take multivitamins during pregnancy. People view this as "insurance" to ensure they get enough nutrients.

Our research, using data from a pregnancy cohort in Queensland, shows that socioeconomic factors influence likelihood of using multivitamins during pregnancy. We found that those who have access to private obstetric care and health insurance, and who eat more meat (all linked to having more money), are more likely to use multivitamins.

This is not surprising given the high cost. The most popular prenatal multivitamin costs a minimum of A$180 when taken a month before conception and throughout pregnancy. Compare that to less than $40 for a supplement containing only folic acid and iodine taken for the same duration.

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

What happens if you have too much?

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

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

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

Folic acid intake above the upper intake level was associated with more short growth in children at birth, reduced levels of children's cognitive development 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 is recommended on a routine basis.

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.

For iodine, about one in four expectant mothers taking multivitamins in our study had very high intake levels, which is associated with lower rates of neurodevelopment in children.

You're most likely getting enough nutrients

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

In high-income countries such as Australia, food is extremely varied. There are also mandatory food fortification programs - folic acid and iodized salt have been used in baked goods since 2009.

In these countries, frequent use of multivitamins may pose a risk to maternal and fetal health. 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 the 28th week of pregnancy, found that those least likely to take supplements were those under 30 and those with lower incomes families. These same groups usually 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 obstetricians and possibly a registered dietitian to focus on adequate intake from each of the five food groups.

Supplements should not replace a nutritious 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 guidelines can also save you money.

Healthcare providers also need to stop routinely recommending those expensive "pink" multivitamins and instead focus on encouraging people to eat healthier. Apart from 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 journal The Conversation.