Until recently, the main supplements recommended for pregnancy were folic acid and iron: maternal folic acid (ideally taken before conception) helps prevent spina bifida and other neural tube defects, while increased blood volume and the developing placenta place large demands on iron stores.
These days, there are specialist multi-vitamin and mineral preparations for pregnancy and breastfeeding, as well as conception. Are these supplements a gimmick, or is there good evidence they're beneficial?
Micronutrient requirements of pregnant women
The National Health and Medical Research Council (NHMRC) lists recommended daily intakes of various nutrients for pregnant and breastfeeding women, based on latest available evidence. The key nutrients at issue for pregnant women are as follows:
Pregnancy increases the need for iron in the diet. Apart from increased vascular blood mass for the mother and placenta, the developing foetus draws iron from the mother to last it through the first five or six months after birth (breast milk is low in iron). Although studies show that absorption of iron can increase substantially during pregnancy, the recommended daily intake (RDI) is 27mg, and vegetarians, vegans and women carrying more than one baby are at risk of iron deficiency.
The RDI for women is 500 micrograms (mcg) for one month before conception and 600mcg for three months after. In 2009, Food Standards mandated that bread be fortified with folic acid, and two slices contains about 80mcg. This will help, but a supplement is still recommended, as are natural sources such as green vegetables and wholegrains.
Iodine is necessary for the normal growth and mental development of a baby, and the RDI for pregnant women is 220mcg and 270mcg for breastfeeding women. After milk producers switched from using iodine-based to chlorine-based cleaners to clean dairy equipment, and more people ditched iodised table salt for gourmet salt – or none at all – iodine deficiency became an issue, with pregnant woman in parts of Australia suffering mild to moderate deficiency in the early 2000s.
Since 2009, bread manufacturers have been required to use iodised salt in all bread except organic bread. This is expected to increase average iodine levels by about 54mcg per day. However, on its own this won’t ensure pregnant or lactating women are getting enough iodine, and a 150mcg supplement is recommended. The NHMRC recommends you avoid kelp and kelp-derived iodine due to mercury poisoning risks.
Vitamin D helps the body absorb and use calcium. The most recent recommendations are that an adequate intake (AI) for all adults up to the age of 70, including pregnant and lactating women, is 15mcg (or 600 international units) of dietary vitamin D per day, with a safe upper limit of 100mcg (4000 IU). While we can get our vitamin D from the sun, deficiency is an emerging health issue in Australia – studies of the general population show that while few people are moderately or severely deficient in vitamin D, a significant minority (23-49%) have a mild deficiency.
The main risks for deficiency are having dark skin and covering up for religious or cultural reasons. People living in colder southern parts of Australia are also susceptible to deficiency. Obesity is another risk factor, and its prevalence is increasing in Australia – a Queensland study found 14% of pregnant women were obese.
Most people will get enough vitamin D by spending 10 minutes in the morning or late afternoon sun with face, arms and hands exposed; a bit longer in winter (15 minutes or 30 minutes in Tasmania) .
The level of vitamin D found in most pregnancy supplements is less than the recommended adequate intake of 600 IU (Ethical Nutrients Pregnancy Support and Swisse Pregnancy Ultivite being the exceptions). So if you’re at increased risk of deficiency, consult your doctor for advice.
A developing foetus needs calcium for healthy bones, teeth, muscles, nerves and heart. Normal levels of recommended calcium intake will suffice, although pregnant teenagers will need extra. For most people, calcium needs can be met through the diet. Women who avoid dairy products or have a vitamin D deficiency may need a supplement.
Vitamin B12 is needed for neurodevelopment. It’s only found in animal products (flesh, eggs and dairy) and some types of algae, so vegans may need vitamin B12 daily supplementation of 250-500 mcg. Ethical Nutrients Pregnancy Support contains 500mcg - however, the supplement contains animal-derived ingredients and so isn’t suitable for vegetarians or vegans.
Omega 3 fatty acids
Many supplements contain fish oil, which provides fatty acids essential for the baby’s neural development. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists currently don’t recommend it in the first trimester, due to a lack of evidence supporting its use and a lack of safety data. But they told us that this position is likely to change soon, with more evidence of its safety now available.
Too much of a good thing?
Some vitamins in excess can cause problems. These include:
Vitamin A is available as retinol or from conversion of beta carotene in brightly coloured fruits and vegetables. The retinol form is found in liver, full-fat dairy products and margarines. The particularly high levels in liver can be toxic and pregnant women are advised to avoid liver and pate for this reason. Vitamin pills tend to contain the beta-carotene form of vitamin A. Avoid those containing retinol.
Vitamin B6 may help relieve nausea, though not necessarily vomiting, associated with morning sickness. Many supplements contain 50mg of vitamin B6, which is much greater than the RDI of 1.9mg/day but at the upper level of recommended intake for pregnant women. A typical balanced diet will give you a few milligrams in addition to this, but it’s extremely unlikely you’d get anywhere near the safe maximum of 100mg per day without additional supplements. More than 100 mg per day in the first trimester may be linked to birth defects involving the baby's arms, legs and nerve development.
The upper intake for iron intake from all sources is 45mg per day, and most supplements have less than this. At higher levels, there is a risk of gastrointestinal upset and constipation, though this can be minimised by taking the pill with food and drinking plenty of water throughout the day. In cases of iron deficiency anaemia, the doctor’s supervision of intake is essential: large amounts of iron can lead to an excessive increase in red blood cells (called haemoconcentration), which thickens blood and slows its flow, causing, paradoxically, the same problems as too little iron: premature birth and low birth weight. Iron supplements are also hazardous for the 1 in 300 people with haemochromatosis, a condition that may not be diganosed in women during their child-bearing years.