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 a standardised location—approximately 2 cm beside the umbilical cord insertion, from the middle layer of placenta midway between maternal and fetal surfaces—in order to reduce the bias related to the physiological difference in gene expression within the same placenta depending on the sampling site.