Open Access
Feature Article

Optimising micronutrients during pregnancy

Open Access
Feature Article

Optimising micronutrients during pregnancy

KAREN P. BEST, MARIA MAKRIDES, ROSALIE GRIVELL

Figures

© michaela besteiger/ stock.adobe.com
© michaela besteiger/ stock.adobe.com
Dr Best is a midwife; and Senior Research Fellow at South Australian Health and Medical Research Institute, Adelaide. Professor Makrides is a dietitian; and Deputy Director and Theme Leader at South Australian Health and Medical Research Institute, Adelaide. Associate Professor Grivell is a Maternal Fetal Medicine Subspecialist; and Matthew Flinders Fellow, College of Medicine and Public Health at Flinders University, Adelaide, SA.

Folate and folic acid

Folate is a B-vitamin that is naturally present in many foods including leafy green vegetables, citrus fruit, breads, cereals and legumes. It serves many important functions and plays a crucial role in cell growth and the formation of DNA. Folic acid is the synthetic, more stable form of folate, and is often added to foods or used in supplements. 

There is consistent scientific evidence that folic acid is of high importance for the prevention of neural tube defects (NTDs), and health authorities around the world recommend supplementation.7 Given that it can take three weeks to increase serum folate to adequate level, folic acid supplementation should be started before conception and continued until neural tube closure, which normally occurs around 28 days after conception. The current evidence-based guidance recommends women take a daily dietary supplement containing 400 micrograms of folic acid for at least one month before trying to become pregnant until 12 weeks of gestation (Figure).3 Prescription of the bioavailable form of folic acid, L-methylfolate, may be advantageous to women diagnosed with genetic polymorphisms that impair the conversion of supplemental folic acid to its active form.8

Despite recommendations for supplementation, many Australian women do not have sufficient folate intake in early pregnancy;9 and for many women, neural tube closure occurs before they confirm their pregnancy. Therefore, mandatory folic acid fortification of bread-making flour was introduced in Australia in 2009. This action has increased folic acid intake in women of reproductive age by around 0.15 to 0.2 mg/day and has reduced the incidence of NTDs by about 14% in states where data are available.10 Even greater reductions in NTDs have been reported in the offspring of Australian Indigenous and teenage women.11 The preventative strategy of adding folic acid to food staples has been adopted by more than 80 countries worldwide.12

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Although routine folic acid supplementation has been universally adopted for the prevention of NTDs, systematic reviews of the available evidence suggest that continuing supplementation beyond the periconceptional period does not improve other pregnancy outcomes such as premature birth, low birth weight or miscarriage.13,14 Similarly, a recent large randomised controlled trial showed that high-dose folic acid supplementation throughout pregnancy did not to reduce the risk of preeclampsia.15 There are no clear benefits for taking higher doses of folic acid or continuing supplementation beyond 12 weeks of pregnancy.

Iodine

Iodine is a trace element that is naturally present in some foods. The main dietary sources of iodine in Australia include bread, eggs, dairy, iodised salt and seafood. Iodine is used by the body to produce thyroid hormones, which are important for the growth and development of the fetal nervous system. During pregnancy (and breastfeeding), thyroid activity increases, therefore, pregnant women have a higher risk of iodine deficiency because of their increased iodine requirement.16 There is no reliable way to measure iodine status in an individual; however, urinary iodine concentration is used as a biomarker to determine iodine status on a population level. 

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Observational studies suggest that mild to moderate iodine deficiency during pregnancy may result in childhood learning difficulties and affect the development of motor skills and hearing.17 The results of the 2004 national survey of school-aged children showed that mild iodine deficiency (based on urinary iodine concentration) had re-emerged in south-eastern parts of Australia.18 In response, in addition to folic acid fortification in 2009, the Australian government also mandated the replacement of non-iodised salt with iodised salt for bread-making. Mandatory fortification has increased levels of iodine in the food supply and improved iodine status in the general population and women of child-bearing age (52% increase).10 Moreover, a consensus-based recommendation was made that women who are considering becoming pregnant, who are pregnant, or are breastfeeding should consume 150 micrograms of iodine per day through supplements, as well as obtaining iodine from a healthy diet (Figure).