INTRODUCTION
Managing adequate intakes of calcium during pregnancy is important in several physiological processes, and reduces the risk of perinatal adverse events such as hypertensive disorders and preterm birth. (1-3) The recommended daily intake (RDI) of calcium is 1000 mg/day for all women of childbearing age. (1) Calcium demands increase substantially during pregnancy, but are met by an increased intestinal absorption, renal reabsorption and mobilization from the maternal skeleton, mediated mostly by an increase in PTH and IGF-I over the course of pregnancy. (4-6) However, these measures are insufficient to compensate for an inadequate intake. Adult women of childbearing age (18-50) have remarkably low intakes of calcium. 22.7-44.5% of women in the Netherlands consume less than the estimated average requirement (EAR) of 750 mg/day. (7) In the UK, 6-8% of women of childbearing age consume even less than the lower reference nutrient intake (LRNI) of 400mg/day. (8) Individuals habitually consuming less than the LRNI are almost certainly deficient of the nutrient concerned. (9) The EAR and recommended daily intake (RDI) are further explained in the supplement.
Calcium supplementation starting from the second or third trimester in women with chronically low intakes reduces risks of gestational hypertension and preeclampsia, with estimated risk reductions of 30% and 50%, respectively. (2, 3, 10) The WHO and Dutch guidelines for pregnancy consultation therefore recommend daily calcium supplementation starting from the 20th week of gestation in women with an inadequate intake. (11, 12) Due to tight regulation of serum calcium levels (2.10-2.55 mmol/L) (13)), there is poor association between dietary and total calcium serum levels. (5, 14) Hence, nutritional screening is the only appropriate method to assess calcium intake. During regular maternal outpatient clinic visits there is neither time nor expertise for elaborate dietary assessments. A simple screening tool for calcium intake could offer a solution, and contribute to better care and prevention through early detection and intervention in women at risk of having an inadequate intake, and with that the improvement of perinatal outcomes and maternal-fetal health. A digital screening tool could also contribute to improved self-management in periconceptional care, by enabling women to assess and improve their own calcium intake, and with that leading to greater health care efficiency and maternal and perinatal outcomes.
To our best knowledge, no studies have been conducted on the development of a calcium-specific FFQ or a prediction model to assess calcium intake in pregnancy. We hypothesize that intake of an adequate amount of calcium can accurately be predicted by a limited number of products.
Therefore, the aim of this study is to develop an effective and simple digital screening tool based on a prediction model for calcium intake in pregnancy, that is suitable for making accurate individual predictions with a minimal number of predictors and can be integrated in existing pregnancy health platforms (e.g. Smarter Pregnancy) to be used by both clinicians and women who are or are planning to become pregnant.