Calcium Supplementation Guidelines for the Third Trimester of Pregnancy

Recommended Dosage and Formulation

The WHO strongly recommends 1.5–2.0 g elemental calcium daily for pregnant women living in populations with low dietary calcium intake (< 900 mg/day) to prevent preeclampsia, a leading cause of maternal mortality worldwide. Strong recommendation 3
In settings where a full 1.5–2.0 g may be impractical, a daily elemental calcium dose of 1.0–1.5 g is advised, adjusted to local dietary calcium patterns. Conditional recommendation 1
Calcium carbonate is the preferred calcium salt because it provides 40 % elemental calcium by weight (versus 21 % for calcium citrate), making it more cost‑effective and requiring fewer tablets. Expert consensus 2
The total daily calcium dose should be split into 2–3 administrations, each containing ≤ 500 mg elemental calcium, to maximize fractional absorption, which declines with larger single doses. Evidence‑based 1

Calcium carbonate should be taken with meals, as gastric acid is required for optimal absorption. Practical guidance 2
Supplementation should begin at the first antenatal contact (regardless of gestational age) and continue through delivery; early initiation may further support placental vascular development. Evidence‑based 1

Patients should be instructed to take calcium supplements together with IFA tablets at the same time to simplify the regimen and improve adherence. Strong recommendation 3
Although calcium can acutely inhibit iron absorption in vitro, real‑world studies show minimal clinical impact, and the adherence benefit of combined dosing outweighs theoretical concerns. Moderate evidence 3
Counseling that calcium and IFA must be taken separately creates an unnecessary barrier and should be avoided. Strong recommendation 3

In populations with low baseline calcium intake, the recommended calcium regimen reduces the risk of preeclampsia by approximately 50 %. High‑quality evidence 2
Additional maternal‑fetal benefits include lower rates of preterm birth, longer gestation, higher neonatal birth weight, and improved maternal bone mineral density in the postpartum period. Expert consensus 2

Calcium citrate should be reserved for women with achlorhydria, those on proton‑pump inhibitors, or those unable to take supplements with meals. Expert consensus 2
When using calcium citrate, prescribe roughly 7.1 g of the salt daily to deliver 1.5 g elemental calcium (or 9.5 g for 2.0 g elemental), divided into 3–4 doses of ≤ 2.4 g per dose. Practical guidance 2
Calcium citrate can be taken with or without food, which is its principal advantage over calcium carbonate. Expert consensus 2

Do not administer the entire daily calcium dose as a single tablet; this leads to poor absorption and diminishes clinical benefit. Practical guidance 2
The upper safety limit for elemental calcium is 2,000–2,500 mg per day; exceeding this may increase the risk of cardiovascular events and kidney stones. Safety recommendation 4
Common side effects are constipation and abdominal bloating; patients should be counseled and, if needed, offered stool softeners. Clinical advice 4

The total recommended calcium intake for pregnant women aged ≥ 19 years is 1,000–1,200 mg per day from all sources (diet plus supplements). Guideline target 5