**4. Materials and Methods**

#### *4.1. Human Research Ethics, Sample Collection and Storage*

Archived placental villous samples, from 20 normotensive controls and 20 women with early-onset PE, were collected at the Royal Women's Hospital Melbourne, Australia for research purposes, and explicitly accessed for this study. The Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) research definition of PE was used to select the PE cohort [43]. Gestation-matched controls were selected from normotensive term pregnancies, idiopathic preterm deliveries or preterm elective deliveries for indications not associated with placental function. All controls were absent of placental pathology and delivered babies with birth weights appropriate for gestational age [44]. The collection and archiving of all samples had the approval of the relevant institutional human research ethics committees in 2000 and 2001 (HREC# 01/46, 00/27). Each woman gave written informed consent for tissue collection and the recording of de-identified demographic information and pregnancy outcomes. Where available, information on maternal age, parity, gestational age, mode of delivery, baby sex, birth weight and placental weight were extracted from electronic records. Sample processing was within 20 min of placental delivery. Villous tissue was dissected from a central placental cotyledon. The decidua was removed before tissues were divided into pieces, snap-frozen in liquid nitrogen and stored at –80 ◦C for future analysis [45].
