High blood pressure which is well controlled generally does not increase the risk of miscarriage. However, certain antihypertensive medications are associated with an increased risk of birth defects. These include angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) and Thiazide diuretics. These should be changed to safer antihypertensives prior to pregnancy. The majority of women with controlled chronic hypertension will, under close supervision and appropriate management, have a successful outcome. Poorly controlled hypertension in the first trimester will significantly increase maternal and fetal morbidity and mortality.