1 Departments of Medicine and Obstetrics and Gynecology, MedStar Georgetown University Hospital and Georgetown University Medical Center, Washington, DC, USA. andrea.f.singer@gunet.georgetown.edu.
2 Department of Obstetrics and Gynecology, MedStar Georgetown University Hospital, Washington, DC, USA. andrea.f.singer@gunet.georgetown.edu.
3 MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, UK.
4 Alan Turing Institute, London, UK.
5 National Osteoporosis Foundation, Arlington, VA, USA.
6 Department of Medicine, University of Pittsburgh and University of Pittsburgh Medical Center, Pittsburgh, PA, USA.