AU: Use is contraindicated.
UK: Use is not recommended during the first trimester of pregnancy and is contraindicated during the second and third trimesters.
US: This drug should not be used during pregnancy unless there are no alternatives and the benefit outweighs the risk to the fetus.

AU TGA pregnancy category: D
US FDA pregnancy category: D

Comments: Adequate methods of contraception should be encouraged.

Animal studies have revealed evidence of fetal toxicity. Neonatal thrombocytopenia or fetal or neonatal jaundice have been reported with maternal thiazide therapy. In humans, use of drugs that act on the renin angiotensin system (RAS) during the second and third trimesters increases fetal and neonatal morbidity and death. There are no controlled data in human pregnancy.

AU TGA pregnancy category D: Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human fetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Accompanying texts should be consulted for further details.

US FDA pregnancy category D: There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

See references

A decision should be made to discontinue breastfeeding or discontinue the drug, taking into account the importance of the drug to the mother.

Excreted into human milk: Yes (hydrochlorothiazide); Unknown (olmesartan)
Excreted into animal milk: Yes (olmesartan)

See references