Sitras et al. investigated the global placental gene expression profile in severe preeclampsia. Twenty-one women were randomly selected from 50 participants with uncomplicated pregnancies to match 21 patients with severe preeclampsia. Five preeclamptic placentas were excluded because of poor RNA quality, leaving 16 preeclamptic placentas for microarray experiments. Chorionic tissue was dissected from the middle layer of placenta midway between maternal and fetal surfaces, approximately 2 cm beside the umbilical cord insertion.