Hydrochlorothiazide in pregnancy, thiazide diuretics may cause an increased risk of congenital defects. Lab tests, including kidney function, blood pressure, and electrolyte levels, may be performed while you use Hydrochlorothiazide, check with your doctor. Hydrochlorothiazide is a type of medicine known as a thiazide diuretic. Hydrochlorothiazide in pregnancy, thiazide diuretics may cause an increased risk of congenital defects. Lab tests, including kidney function, blood pressure, and electrolyte levels, may be performed while you use Hydrochlorothiazide, check with your doctor.