A 38-year-old woman is in her first pregnancy, which has been uneventful until the 34th week, when she develops swelling of feet and hands. An obstetric check-up reveals that she also has hypeension and proteinuria. Laboratory analysis shows elevated aspaate aminotransferase (AST) and alanine aminotransferase (ALT) and slightly decreased platelets. The initial event in the pathogenesis of her condition is thought to be which of the following?

This patient's condition is a classic third trimester complication referred to as toxemia of pregnancy, or preeclampsia. It occurs in 6% of all pregnancies but is more frequent in primiparas. Although the pathogenesis is still unclear, the first event appears to be placental ischemia, probably due to abnormalities in the trophoblast and alterations in the maturation of placental vessels. The trophoblast of invading placental vessels fails to acquire the characteristics of normal endothelial cells, with subsequent alterations in blood flow. Placental ischemia then triggers the release of thromboplastic substances, increases renin synthesis, and reduces prostaglandin E levels. Chorioamnionitis is an infection of chorioamniotic membranes due to bacteria that ascend through the vaginal canal. This is an impoant cause of spontaneous aboion in the second and third trimester, but it plays no role in the pathogenesis of toxemia of pregnancy. The release of thromboplastic substances may cause disseminated intravascular coagulation (DIC). Increased renin and reduced prostaglandin E mediate increased sensitivity to angiotensin, leading to maternal hypeension.