1 Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Nuffield Department of Women's & Reproductive Health, University of Oxford, Women's Centre, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom; Oxford Maternal and Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, United Kingdom; St George's University Hospitals National Health Services Foundation Trust, London, United Kingdom. Electronic address: aris.papageorghiou@wrh.ox.ac.uk.
2 Centre for Environmental Research and Community health, School of Public Health, University of California, Berkeley, CA.
3 Nuffield Department of Women's & Reproductive Health, University of Oxford, Oxford, United Kingdom; Oxford Maternal and Perinatal Health Institute, Green Templeton College, University of Oxford, Oxford, United Kingdom.