Australia and New Zealand are the only countries to have combined policies of mandatory iodine fortification of foods and recommended for supplementation during pregnancy and lactation. This double-barrelled approach was recently brought into question by an evaluation of iodine nutrition during pregnancy in South Australia, which showed that children of pregnant women whose iodine intake was at the extreme ends (either too low or too high) had poorer performance on cognitive and language tests compared with children of pregnant women with adequate iodine intake levels.19 A randomised controlled trial to determine the effect of iodine supplementation in pregnancy on early childhood neurodevelopment is underway in Australia and will provide evidence regarding optimal iodine intakes for pregnant women (https://clinicaltrials.gov/ct2/show/NCT04586348).
There are limited single-nutrient iodine preparations and most women will select a multivitamin and mineral prenatal supplement containing iodine. Women should be advised not to exceed recommended intakes for all supplements, but iodine is a particular concern. Seaweed and kelp supplements are high in iodine but can contain toxic levels and are therefore not recommended during pregnancy.
Fish and fish oils are rich sources of omega-3 LCPUFAs, particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In population studies, intake of omega-3 LCPUFAs in pregnancy has been associated with longer pregnancy and improved perinatal outcomes.20, 21 However, pregnant women are reluctant to increase their fish intake because of concerns around mercury levels in seafood. Women may even decrease their intake because of these concerns and confusing advisories.22 Women can safely consume two to three serves of cooked seafood per week by avoiding the larger, deep sea predatory fish (Table 3).23 Additionally, canned fish such as tuna and salmon are low in mercury and can be consumed more regularly.
The recent Cochrane Review assessing the effects of omega-3 LCPUFAs (taken as supplements or as dietary additions during pregnancy) on pregnancy outcomes showed a lower risk of preterm birth (<37 weeks) and early preterm birth (<34 weeks) for women receiving omega-3 LCPUFAs compared with those not receiving omega-3 LCPUFAs.24 Preterm birth at less than 37 weeks was reduced by 11% in women who received omega-3 LCPUFAs compared with women who did not receive omega-3 (risk ratio [RR], 0.89; 95% confidence interval [CI], 0.81 to 0.97) and early preterm birth at less than 34 weeks was reduced by 42% (RR, 0.58; 95% CI, 0.44 to 0.77). Many of the trials in this review were conducted before prenatal supplementation with low levels of omega-3 LCPUFA was common. The largest and most recent Australian trial suggests that routine omega-3 supplementation of all women in pregnancy will not be effective in reducing overall premature birth rates, rather it will only benefit women with a low omega-3 status in early pregnancy in this way.25-27 Women with sufficient omega-3 status in early pregnancy are already at lower risk of preterm birth and further omega-3 supplementation may increase this risk.26 The latest update of the Australian Pregnancy Care Guidelines includes an evidence-based recommendation for women with low omega-3 levels to take an omega-3 supplement (800 mg DHA and 100 mg EPA) to reduce their risk of preterm birth.3
Identifying women with low omega-3 status by assessing diet is difficult unless they are vegans or vegetarians who also do not consume eggs. In South Australia, a state-wide program of serum omega-3 screening in early pregnancy commenced in April 2021. This screening program will identify women with low status and guide their treatment to assess the effectiveness of a precision nutrition approach to reducing preterm birth on a population basis.
Vitamin D (also known as calciferol or D2 and D3) is a fat-soluble vitamin that is found in only a small number of foods (namely fish-liver oils, fatty fish, mushrooms, egg yolks and fortified foods), but is easily synthesised cutaneously by humans through exposure to sunlight.3