Folate is a key pregnancy vitamin, but not all supplements are created equal. Here's what you need to know

Navigating pregnancy and early parenting advice can be overwhelming — and for many parents, the confusion begins in the supplement aisle.

One of the first things women planning a pregnancy or in the early stages of one are advised to do is take a prenatal supplement containing folic acid — the synthetic version of folate, or vitamin B9 — and iodine.

Iodine is essential for a baby's brain and nervous system development, while folate is particularly important in early pregnancy to help prevent neural tube defects such as spina bifida.

But there are scores of supplements to choose from, many of which contain a plethora of vitamins and minerals, sometimes in vastly different amounts.

Adding to the confusion is the fact many newer supplement companies substitute folic acid with methylfolate — a lesser-studied form of folate, often claimed to be more easily absorbed — and usually at heftier prices.

"It's very hard standing in the pharmacy to negotiate those claims, to understand what is effective, what is cost-effective, and what is safe," Alexis Shub, obstetrician and maternal fetal medicine specialist at the Mercy Hospital for Women, said.

So what ingredients are essential in a prenatal supplement? And when should you start taking one?

What supplements are recommended in pre-conception and pregnancy?

National pregnancy care guidelines recommended women take 400–600 micrograms of folic acid per day ideally from four weeks before conception and throughout the first 12 weeks of pregnancy.

For women at increased risk of having a pregnancy affected by neural tube defects — such as those with a family history, or who have diabetes — a higher dose (5 milligrams per day) may be recommended.

When it comes to iodine, all women are advised to take a daily supplement containing 150 micrograms when they're planning a pregnancy, pregnant and breastfeeding. (Women with a pre-existing thyroid disorder should seek medical advice first.)

If you haven't taken a supplement prior to conception — and it's estimated half of all pregnancies in Australia are unplanned — it's recommended you start once you become aware you're pregnant.

To reduce the risk of nutrient deficiencies and neural tube defects across the population, bread products in Australia are also fortified with folic acid and iodine. Since mandatory fortification was introduced in 2009, neural tube defects have fallen by 14 per cent.

What's the difference between folic acid and other types of folate?

When you consume folate through food or folic acid, your body converts it into methylfolate (also known as L-5-methyltetrahydrofolate or 5-MTHF). It does this with the help of an enzyme made by the MTHFR gene.

In recent years, a growing number of supplement companies have developed prenatal formulations that contain methylfolate instead of folic acid.

Typically, they're promoted as being more "bioavailable" (or easier to absorb) and therefore a better choice, especially for people with MTHFR gene variations, which can slightly reduce the gene's effectiveness.

But Shelley Wilkinson, a prenatal dietitian and an obstetric medicine researcher at the University of Queensland, said that wasn't the case, and stressed that folic acid was the only form of folate that had been shown in trials to help prevent neural tube defects. 

"The majority of people will be able to get the folate they need from [folic acid] supplements and food," Dr Wilkinson said.

Australian pregnancy guidelines (and other international health authorities) note that pregnant women with MTHFR variations — which are estimated to affect 60–70 per cent of the population — can still process all types of folate, including folic acid.

According Dr Shub: "When people look at blood levels of folate in women with MTHFR variants, they're the same when they've taken folic acid as women who don't have that mutation."

It shouldn't be assumed, she said, that methylfolate supplements — which are typically more expensive — work in the same way as folic acid to support neural tube development.

"The other problem with [methylfolate] is that it's not as stable … it's susceptible to changes to light and temperature, and so what you think you're getting in your vitamin might not be what's actually in there."

Claire Roberts, who leads the Pregnancy Health and Beyond Laboratory at Flinders University, said while supplements containing methylfolate were "likely" to help to prevent neural tube defects, and may even be beneficial for some women, there wasn't enough evidence to confirm that.

What about other vitamins and minerals?

Vitamin D testing during pregnancy used to be recommended, as was supplementation for women found to be deficient, but Australia's national pregnancy care guidelines were recently updated to advise against this.

The guidelines note that while routine vitamin D supplementation during pregnancy "may offer some benefit", there's insufficient evidence to recommend testing or supplementation as part of standard pregnancy care.

When it comes to supplementing other key vitamins and minerals, the guidelines currently recommend:

• Calcium: recommended for women at risk of high blood pressure
• Iron: recommended for pregnant women based on blood test results at 28 weeks
• Vitamin B6: not enough evidence to detect clinical benefits in pregnancy, though it may help to reduce nausea (high doses, however, can lead to serious adverse outcomes — see below)
• Vitamin B12: not enough evidence to draw conclusions, though it may benefit women who are vegetarian or vegan
• Magnesium: not routinely recommended
• Omega-3 fatty acids: may reduce the risk of preterm birth in women who are low in omega-3
• Vitamin A and E: high-dose supplementation not routinely recommended for pregnant women with no identified deficiency or clinical need
• Vitamin C: high-dose supplementation not routinely recommended for pregnant women with adequate dietary intake
• Zinc: guideline under review
• Other minerals (e.g. selenium): not enough evidence to draw conclusions
• Probiotics: guideline under review.

With the exception of folic acid and iodine, Dr Shub said there was limited evidence for many of the ingredients in prenatal supplements, and that for the majority of pregnant women (without risk factors or known deficiencies), a balanced diet would provide most of the nutrients they needed.

"If women are trying to do the best thing in their pregnancy, a healthy diet and exercise is still the best way to go. Although that can be difficult, spending money on [multi]vitamins is probably not a good use of money."

Dr Wilkinson agreed: "There's a lot you can get from a well-planned diet — omega-3, so DHA and EPA [two types of omega-3 fatty acids] can be obtained, and choline [a nutrient important for fetal development] … is in meat, fish, poultry, dairy, eggs, green leafy veggies, legumes, and potatoes."

Evidence for choline supplementation is mixed, though some experts suggest it may help women meet their recommended daily intake.

Dr Wilkinson acknowledged that many Australians struggled to get enough fruit and vegetables in their diet, and encouraged pregnant women concerned about their nutrient intake to work with an accredited dietitian or their healthcare provider to create a "food-first approach".

Why more is not always better

Dr Wilkinson said while many women took pregnancy supplements containing a range of vitamins and minerals for "peace of mind", there was a risk of consuming too much, particularly if women were taking a combination of products.

"We've seen it with vitamin B6, which can be in magnesium [supplements], energy drinks, multivitamins and morning sickness tablets."

She said she had seen some pregnant women who were taking more than 50 times the recommended daily amount of vitamin B6, which in high doses can cause irreversible nerve damage.

Australia's national medicines regulator recently reported that high doses of B6 could lead to adverse pregnancy outcomes, particularly in the first trimester.

High doses of vitamin A, C and E can also be dangerous during pregnancy: "It's why women should not take non-pregnancy multivitamins," Dr Shub said.

Unnecessarily high doses of recommended vitamins can also pose potential health risks, said Professor Roberts, whose research has found a link between excess maternal folate levels and a rise in gestational diabetes.

In a small 2023 study, Dr Wilkinson and her colleagues found 5 per cent of pregnant women exceeded the safe upper level of intake for folic acid (1,000 micrograms per day), and almost 50 per cent exceeded the upper limit for iron.

While folic acid supplementation is only recommended during the first trimester, research suggests many women continue to take it in the second and third trimesters as part of a prenatal multivitamin.

Dr Wilkinson said this was generally OK, given daily folate requirements were increased during pregnancy, but advised women against taking "large amounts" that might put their daily consumption above the recommended upper limit.

Calls for better regulation and labelling

Unlike registered medicines, most vitamin supplements in Australia aren't evaluated by the Therapeutic Goods Administration before they hit the market.

The TGA regulates the safety and quality of AUST L products by limiting them to use only pre-approved low-risk ingredients, however many are not assessed for efficacy, placing them in a regulatory "grey area", Dr Wilkinson said.

She and Professor Roberts said they'd like to see increased regulation of prenatal supplements to help consumers make evidence-based choices.

"Women want to do the best thing for their baby, and they have an awful lot of guilt if they don't," Professor Roberts said.

Dr Wilkinson added that increased oversight could help women avoid paying for products they didn't need.

"It could be a lot cheaper and easier if you took what you needed, rather than what you're marketed."