Why should ACE inhibitors and ARBs be avoided during pregnancy?

ACE inhibitors and ARBs are contraindicated in pregnancy because they can cause fetal renal damage, oligohydramnios meaning low amniotic fluid, skull defects, lung hypoplasia, and fetal death, particularly in the second and third trimesters. These drugs cross the placenta and disrupt the fetal renin-angiotensin system, which is essential for normal kidney development and blood pressure regulation in the fetus.