Preterm preeclampsia is an important cause of maternal and perinatal death and complications. It is uncertain whether the intake of low-dose aspirin during preg- nancy reduces the risk of preterm preeclampsia

n engl j med nejm.org 1 From King’s College Hospital (D.L.R., L.C.P., N.O., A.S., R.A., K.H.N.), Homerton University Hospital (S.C.), North Middlesex University Hospital (D.J.), and University College London Comprehensive Clinical Trials Unit (K.M.), London, University of Exeter, Exeter (D.W.), Medway Maritime Hospital, Gillingham (R.A.), and Southend University Hospital, Westcliff-on-Sea (M.S.) — all in the United Kingdom; Chinese University of Hong Kong, Hong Kong (L.C.P.); Hospital Clínico Universitario Virgen de la Arrixaca, Murcia (C.P.M.), Hospital Universitario San Cecilio, Granada (F.S.M.), and Hospiten Group, Tenerife (W.P.) — all in Spain; Ospedale Maggiore Policlinico, Milan (N.P.); University Hospital Brugmann, Université Libre de Bruxelles, Brussels (J.C.J.); Attikon University Hospital, Athens (G.P.); Rabin Medical Center, Petach Tikva (K.T.-G.), and HyLabs Diagnostics, Rehovot (H.M.) — both in Israel; and University of Iceland, Reykjavik (S.G.). Address reprint requests to Dr. Nicolaides at the Harris Birthright Research Centre for Fetal Medicine, Fetal Medicine Research Institute, King’s College Hospital, Denmark Hill, London SE5 8BB, United Kingdom, or at kypros@ fetalmedicine . com.