Calcium IS Absolutely Needed During Pregnancy
Calcium supplementation during pregnancy is essential and strongly recommended by the WHO, particularly in populations with low dietary calcium intake, as it reduces preeclampsia risk by approximately 50% and addresses a leading cause of maternal mortality globally. 1
Why Calcium Is Critical
Calcium is not optional during pregnancy—it serves multiple vital functions:
Prevents preeclampsia and eclampsia: The WHO issued a strong recommendation based on moderate-quality evidence from meta-analyses showing calcium supplementation prevents approximately half of preeclampsia cases, which is the second leading cause of maternal mortality worldwide. 1
Supports fetal skeletal development: The developing fetus requires 50-330 mg of calcium daily, with approximately 30 g transferred to the fetus during gestation for bone formation. 1, 2
Protects maternal bone health: Pregnancy and lactation cause transient lowered bone mineral density and increased bone resorption, especially during the third trimester and throughout lactation. 3
Reduces additional complications: Calcium supplementation is associated with reduced preterm birth risk, longer pregnancy duration, higher neonatal birth weight, and improved maternal bone mineral density postpartum. 4, 5
Recommended Dosing Regimen
Prescribe 1.0-1.5 g elemental calcium daily, divided into doses of ≤500 mg per administration. 1, 6, 7
The WHO originally recommended 1.5-2.0 g daily, but lower doses of 1.0-1.5 g are likely sufficient and offer better adherence while maintaining clinical benefits. 6, 4
Divide into 3 doses throughout the day (not exceeding 500 mg elemental calcium per dose) to maximize absorption, as fractional calcium absorption decreases significantly with larger single doses. 1, 4
Optimal Formulation
Use calcium carbonate as the preferred formulation. 1, 6, 7
Calcium carbonate contains 40% elemental calcium by weight compared to only 21% in calcium citrate, making it more cost-effective and requiring fewer pills. 1, 4
Calcium carbonate is cheaper and highly bioavailable, though it should ideally be taken with meals for optimal absorption. 1
Reserve calcium citrate for patients with achlorhydria, those taking proton pump inhibitors, or those who cannot reliably take supplements with meals. 4
When to Start and Stop
Initiate calcium supplementation at the first antenatal care visit, regardless of gestational age, and continue until delivery. 1, 6, 7
While the WHO recommendation specifies starting at 20 weeks' gestation (based on the timing used in meta-analyses), pragmatic implementation should begin at first contact with the health system. 1, 7
Starting earlier may provide additional benefit by modulating placental vascularization and systemic vasomotor activity. 1, 7
Do not withhold calcium from women who present after 20 weeks—supplementation beyond this timepoint is still beneficial. 7
Integration with Iron and Folic Acid
Administer calcium together with iron and folic acid (IFA) supplements—do NOT counsel patients to separate them. 1, 6
This is a critical practical point that differs from older guidance:
While calcium acutely inhibits iron absorption in short-term studies, the clinical effects over longer periods are minimal due to adaptive responses in iron regulatory mechanisms. 1
Requiring separation of calcium and IFA would necessitate at least 4 separate administrations per day, dramatically reducing adherence to both supplements. 1
The theoretical concern about calcium-iron interaction is outweighed by the practical benefit of simplified regimens and improved compliance. 4
Who Needs Supplementation
In most low- and middle-income countries, assume calcium supplementation is needed unless local dietary studies indicate otherwise. 1
In 35 of 42 studies from low- and middle-income countries, mean calcium intake was <900 mg/day, consistently across Asia, Africa, and Latin America. 1
The average calcium consumption in Western countries is approximately 800 mg/day in young women, below the recommended 1,000 mg/day for pregnant women. 2
Women with chronic autoimmune disorders, those on low-molecular-weight heparin therapy, lactose intolerance, or those who avoid dairy products should receive 500-1,000 mg supplemental calcium in addition to dietary measures. 2
Common Pitfalls to Avoid
Don't create overly complex schedules: Separating calcium from iron supplements reduces adherence without clear clinical benefit. 7
Don't delay waiting for 20 weeks: If a woman presents earlier, start immediately. 7
Don't use excessive single doses: Keep individual doses ≤500 mg elemental calcium to optimize absorption. 1, 4
Don't assume adequate dietary intake: Most developing countries and many women in developed countries have insufficient calcium intake. 1, 8
Safety Considerations
Calcium supplementation is generally safe with rare side effects:
Increased risk of HELLP syndrome (hemolysis, elevated liver enzymes, low platelet count) has been reported in 2 studies, though extremely few cases occurred. 1, 6
Postnatal bone resorption has been observed in some populations. 1
The benefits substantially outweigh these rare risks, particularly in preventing maternal mortality from preeclampsia. 6
Dietary Counseling as Adjunct
While supplementation is necessary in most settings, dietary counseling should complement it:
Encourage 3-4 servings of dairy products (milk, yogurt, cheese) or calcium-rich alternatives daily. 2
Recommend calcium-rich mineral waters and leafy greens like kale. 3
The feasibility of meeting requirements through dietary counseling alone is remote in many low-income settings given limited access to calcium-rich foods. 1