Clinical implications
The screening tool has an explicit focus on dairy products for calcium intake, which are the most important sources of calcium in a Western-style diet, but not in plant based or non-Western-style diets. The tool could therefore underestimate calcium intake in women with non-Western dietary habits or a plant based diet. However, the average dietary calcium intake in Asian, African and South American countries generally ranges between 400-700 mg/day, and women with a plant based diet have shown to consistently have calcium intakes below the RDI and EAR. (33, 34) This indicates that non-dairy sources of calcium on its own are probably not sufficient to meet calcium requirements. The classification of these diets as having an inadequate calcium intakes might therefore be an appropriate outcome of the tool. However, the FFQ does not account for calcium fortified foods and drinks or supplements. Hence, calcium intake is likely to be underestimated in women who rely on fortified products or supplements to meet dietary requirements.
Our prediction model has a relatively low negative predictive value, especially compared to other test accuracy measures. In the selection of the optimal cut of probability we prioritized positive predictive value and specificity over negative predictive value and sensitivity, based on a benefit-risk assessment of an increased calcium intake in pregnancy through both supplementation or dietary intervention. Increasing calcium intake in pregnant women with inadequate intakes has explicit beneficial effects on bones, nerves and cardiovascular health, and gives a risk reduction of pre-eclampsia (RR 0.51) and gestational hypertension (RR 0.70). (10) The tolerable upper intake level of calcium is 2500 mg/day (35), which is nearly impossible to reach through dietary intake alone. All interventions that focus on dietary counselling to improve calcium intake are therefore considered safe. In contrast, the possible risks of calcium supplementation are not completely clear, though harmful effects such as cardiovascular event, carcinoma, and kidney stones are only reported in older patients, and with doses of >1000 mg/day. (36) Lower dosages have proven to be sufficient for the prevention of both preeclampsia and gestational hypertension. (3, 10) In summary, calcium supplementation appears to be harmless for the target population, especially when using low to moderate dosages. Based on these considerations, we prefer a tool that improperly classifies women as having an inadequate calcium intake over a tool that erroneously classifies women as having an adequate calcium intake.
Current guidelines recommend calcium supplementation starting from the 20th week of gestation in women with an inadequate calcium intake. The 20 week limit has been established because no effect of supplementation in earlier stages of pregnancy has been scientifically proven. The presented screening tool is developed to primarily facilitate the implementation of current guidelines. For this purpose, it can be used to assess calcium intake at around 20 weeks of gestation. However, the tool’s ability to predict calcium intake levels is not limited to this gestational age. Although there is no scientific evidence, beneficial effects of an adequate calcium intake on embryonic growth and placentation cannot be precluded. Moreover, though current guidelines for pregnant women recommend the use of calcium supplements, we want to encourage clinicians to aim for dietary advises or interventions first. Calcium intake can very well be increased through dietary intake alone, which is not only safer, but can also be part of an overall healthier diet. While supplementation tackles isolated micronutrients, dietary improvements can tackle a range of macro- and micronutrients and improve general fitness and health. When aiming for dietary improvements, it is presumably rewarding to start interventions periconceptionally, providing women with the needed time frame to make adjustments in their diet and lifestyle. For this purpose, the screening tool can also be used during preconceptional hospital or midwife visits, at the general practitioner’s office or at outpatient clinics for lifestyle care. (37) By using an early intervention strategy focused on diet and lifestyle, risks of supplementation are diminished, general health is improved and possible beneficial effects even in the early stages of pregnancy can be achieved.