**2.3 Study population**

We studied first trimester data in 90 pregnant women who later developed PE and 100 women who did not. Participants were chosen from a large prospective observational study of women attending the HTH prenatal clinic for early prediction of pregnancies that are prone to develop problems. Women with pregnancies between 11 and 13 weeks of gestation were invited to take part in the study. Participants' maternal characteristics and medical histories were documented.
