In Australia, practice recommendations are for routine supplementation of iodine and folic acid, while recommendations for other vitamins and minerals differ from one pregnant woman to another.
Supplementation is also restricted to those with low dietary intake or established micronutrient deficiencies. However, many women take complex pregnancy multivitamins to avoid potential micronutrient deficiencies.
Therefore, in one study, researchers at the University of Adelaide conducted a review of the existing evidence and special considerations for the aforementioned vitamins and minerals on pregnancy outcomes, in order to evaluate the appropriateness of certain individual and multicomponent vitamin and mineral supplements.
Folic acid supplementation in the peri-conceptional and gestational periods is recommended by health professionals as it prevents certain major congenital malformations, especially neural tube defects, as folate is crucial during periods of rapid growth.
However, the researchers also reported that "a meta-analysis of 31 trials of folic acid supplementation throughout pregnancy found no conclusive evidence of benefit with respect to any pregnancy outcomes", adding that "further trials are required to determine the effects of folic acid supplementation throughout pregnancy on other prevalent pregnancy complications", such as pre-eclampsia and hypertensive disorders.
Doctors also recommend vitamin D supplementation, as its deficiency is linked to higher risk of pregnancy complications, such as low birth weight and pre-eclampsia. Maternal vitamin D deficiency has also been associated with the onset of diseases later in life, such as asthma and type 1 diabetes.
While the evidence so far was said to be insufficient to inform clinical or policy recommendations for supplementation in pregnancy, the researchers advised that pregnant women and women planning to conceive be assessed for vitamin D deficiency based on established risk factors.
Previous trials have shown that high calcium intake significantly lowers the risk of pre-term birth, but has no impact on the risk of infants being born smaller than average, said the researchers.
With anaemia a prevalent issue among pregnant women, particularly in developing countries, reducing the incidence of maternal iron deficiency is considered a priority for organisations like the WHO.
However, routine supplementation of iron is not recommended, with no evidence that it helps reduce 'adverse perinatal outcomes'.
Despite this, it may be able to reduce the risk of preterm birth or low birth weight in areas where nutritional intake is lacking and the risk of anaemia or adverse perinatal outcomes is much greater, such as in developing nations, said the paper.
Maternal iodine deficiency is said to be responsible for irreversible damage to a child's physical and mental development. As such 150 micrograms of iodine supplementation daily is recommended for both pregnant and lactating women, and mandatory where deficiency is widespread.
Still, the researchers wrote that the evidence of iodine’s benefits for pregnant women and their offspring was 'inconclusive', as there were insufficient RCTs on outcomes like pre-term birth or pre-eclampsia.
Multiple issues with multivitamins
They also reported that often, supplementation with multivitamins may lead to excessive intake of vitamins and minerals, which could trigger adverse outcomes.
For instance, combined supplementation of vitamins C and E between 12 and 18 weeks of gestation has been found to raise the risk of foetal loss or perinatal death, added the paper.
At the same time, they states a high intake of vitamin A during pregnancy has been linked with a higher risk of congenital malformation.
The researchers noted that a lack of high quality, large RCTs kept them from evaluating the benefits or possible harm of routine vitamin and mineral supplementation during pregnancy, and advised a cautious approach to widespread routine supplementation.
The researchers concluded: "At present, only folic acid and iodine are recommended for routine supplementation for all women. Intake of other vitamins and minerals, such as iron, calcium and vitamin D, are dependent on a woman's abilities to meet recommended dietary intakes based on nutritional intake alone, or on identified nutritional deficiencies.
"Although multivitamin use is common in pregnancy, there is a lack of data supporting widespread use. Pharmacists should be aware of special considerations regarding vitamin and mineral supplementation in pregnancy and be prepared to provide balanced and up-to-date information to women."
However, another study by the University of Adelaide, published in the journal Midwifery, explored the beliefs of women who took prenatal dietary supplements — and pointed to their benefits.
The study used 10 focus group discussions and two in-depth interviews among 40 women aged 21 to 45, who were either pregnant or had given birth less than 12 months ago, with the aim of better understanding the psychosocial factors behind prenatal vitamin and mineral supplementation.
The researchers found that the participants generally believed supplements to be an easier and more reliable nutrient source than food alone, and used prenatal dietary supplementation as 'insurance', i.e., to ensure sufficient nutrition for themselves and their offspring in order to optimise health and avoid adverse birth outcomes.
The authors wrote: "While some women acknowledged that lack of supplementation is unlikely to result in adverse pregnancy outcomes, they took supplements as a precaution, to avoid feelings of guilt and regret in the event that any adverse birth outcomes did occur.
"Women often had little knowledge of how to ensure an adequate nutrient intake from foods alone during pregnancy and turned to supplementation as an insurance policy."
They then called for further research using larger and more representative samples, so intervention strategies could be tailored to different sub-groups of women.
Source: Journal of Pharmacy Practice and Research
"Vitamin and mineral supplementation in pregnancy: evidence to practice"
Authors: Rebecca L. Wilson, et al.