Vitamin D has specific functions, including bone and muscle development, and in pregnancy plays a role in fetal calcium metabolism and bone development. Vitamin D deficiency in pregnancy may be associated with adverse pregnancy outcomes, particularly hypertensive disorders, preeclampsia and gestational diabetes for women and small for gestational age for neonates.28 Varying policies and practices are in place internationally to screen for and treat vitamin D deficiency in pregnancy including universal supplementation (for high-risk populations); screening serum levels in all women and treating those labelled as deficient; and screening by risk factors, assessing serum levels and treating those who are deficient.28
A recent Cochrane review examining whether vitamin D supplementation during pregnancy, alone or in combination with calcium or other vitamins and minerals, could safely improve maternal and neonatal outcomes concluded that supplementation with vitamin D alone probably reduced the risk of preeclampsia, gestational diabetes and low birth weight but had no impact on neonatal health outcomes.29 Further rigorous, high-quality and larger randomised trials are needed to evaluate the effects of vitamin D supplementation in pregnancy, particularly in relation to the risk of maternal adverse events.29
Routine vitamin D supplementation is not currently recommended for the general population in Australia. Pregnancy care guidelines in many state and territory jurisdictions recommend screening via blood/serum levels at the antenatal booking visit and treating women when serum levels indicate deficiency.
Iron deficiency is the most widespread nutritional deficiency during pregnancy and the leading cause of anaemia. Anaemia in pregnancy is common, occurring in up to 40% of pregnancies and may be associated with significant maternal and perinatal morbidity. When anaemia in pregnancy is identified and managed appropriately, maternal outcomes improve.30
A recent Cochrane review comparing the effects of daily oral iron supplements with no iron supplement and placebo suggested that preventive iron supplementation during pregnancy reduces maternal anaemia at term by 70% (RR, 0.30; 95% CI, 0.19 to 0.46,), iron deficiency anaemia at term by 67% (RR, 0.33; 95% CI, 0.16 to 0.69) and iron deficiency at term by 57% (RR, 0.43; 95% CI, 0.27 to 0.66).30 The impact on pregnancy outcomes is less clear, with no statistically significant results seen for maternal or neonatal outcomes.30 As such, in most populations it is more appropriate to screen women for iron deficiency by haemoglobin concentration initially. Further testing includes full blood count (if this has not already been conducted), serum ferritin level and specific tests for folate and vitamin B12 levels, if mean cell volume is high.3 Women subsequently identified as iron deficient can then be treated appropriately. Oral iron supplementation remains first-line treatment for iron deficiency anaemia identified in the antenatal period. Intravenous iron should be offered to women who do not respond to oral iron or who are unable to comply with therapy.31
General practitioners are well placed to provide both planned and opportunistic prepregnancy and early pregnancy nutritional advice to women throughout their reproductive years. For all women of reproductive age, a dietary history with focus on specific risk factors will assist GPs in identifying women who may be at risk for micronutrient deficiency. Advice on and assistance to improve diet quality will provide significant nutritional benefit, after which specific treatments can be offered when indicated. Referral to a dietitian may be helpful, for practical advice and support for pregnant women with deficiencies. For women planning a pregnancy and those in early pregnancy, unless there are specific risk factors (i.e. restrictive diets), micronutrient needs can be met with a balanced diet with the addition of a few core food groups or serves of core foods. Many pregnant women take a multivitamin supplement from early pregnancy or while trying to conceive. These supplements contain most of the individual vitamins/minerals discussed in this article, so when providing advice, consider which multivitamins a woman is already taking or planning to take. For many micronutrients, excessive intake can be a concern and should be avoided in pregnancy. MT