Calcium Supplementation Timing in Pregnancy
Calcium supplementation should be initiated at the first antenatal care visit, regardless of gestational age, and continued until delivery. 1
WHO Guideline-Based Timing
The World Health Organization formally recommends initiating calcium supplementation at 20 weeks' gestation, based on the timing used in the meta-analyses that established the evidence base for preeclampsia prevention. 1 However, this 20-week threshold does not represent a clinically optimal cutoff, as the underlying studies did not specifically examine whether different timing affects outcomes. 1
Practical Implementation: Start at First Contact
From a pragmatic standpoint, calcium supplementation should begin at the first antenatal care visit, even if this occurs before 20 weeks' gestation. 1 This approach offers several advantages:
- Simplifies the regimen by synchronizing calcium with iron supplementation, which is recommended to begin as early as possible in pregnancy 1
- Reduces complexity and confusion that would arise from having two different supplementation protocols with different start times 1
- Accommodates late presenters, as many women in low-resource settings first seek antenatal care after 20 weeks' gestation, and they should still receive calcium supplementation 1
- May provide additional benefit, as the mechanism of calcium supplementation involves modulation of placental vascularization and systemic vasomotor activity, suggesting that earlier (even periconceptional) supplementation could be more beneficial 1
Dosing and Administration Details
- Dose: 1.0-1.5 g elemental calcium daily, divided into doses of ≤500 mg per administration to maximize absorption 2
- Formulation: Calcium carbonate is preferred due to cost-effectiveness and higher elemental calcium content 2
- Duration: Continue from first contact until delivery 1, 2
- Co-administration: Can be taken together with iron and folic acid supplements to simplify the regimen and improve adherence 1, 2
Clinical Context: Why Calcium Matters
Calcium supplementation reduces the risk of preeclampsia by approximately 50%, particularly in populations with low dietary calcium intake. 2 This intervention addresses a leading cause of maternal mortality globally. 2
Common Pitfalls to Avoid
- Don't delay supplementation waiting for 20 weeks if the woman presents earlier—start immediately 1
- Don't withhold calcium from women who present after 20 weeks—supplementation beyond this timepoint is still beneficial 1
- Don't create overly complex schedules by separating calcium from iron supplements, as this reduces adherence without clear clinical benefit 1