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.