There are no controlled data using calcium carbonate in human pregnancy; however, based on years of use, the malformative risk is unlikely in humans. In some patients, permanent hypercalcemia has resulted in adverse events on the fetus. Animal studies using magnesium carbonate have not been reported. There are no controlled data using either of the drugs, alone or in combination, in human pregnancy.

The manufacturer makes no recommendation regarding use during pregnancy.

AU pregnancy category: Not formally assigned to a pregnancy category.
US FDA pregnancy category: Not formally assigned to a pregnancy category.

Comment: Some experts state that patients should consider limiting their daily intake of calcium to 2500 mg.

See references

The manufacturer makes no recommendation regarding use during lactation.

Excreted into human milk: Yes

Comments:
-Calcium carbonate has been used without apparent harmful effects in the nursing infant.
-The WHO considers aluminum hydroxide compatible with breastfeeding.
-Some authorities recommend monitoring breastfed infants for adverse effects.

See references