1. Department of Epidemiology, Emory University , Atlanta, Georgia , USA
2. Division of Epidemiology and Biostatistics, School of Public Health, University of Cape Town , Cape Town , South Africa
3. Department of Obstetrics & Gynaecology, University of Cape Town, Groote Schuur and New Somerset Hospitals , Cape Town , South Africa
4. Biomedical Research and Innovation Platform, South African Medical Research Council , Cape Town , South Africa
5. Health through Physical Activity, Lifestyle and Sport Research Centre, Division of Physiological Sciences, Department of Human Biology, University of Cape Town , Cape Town , South Africa
6. Department of Obstetrics and Gynecology and Medicine, Warren Alpert School of Medicine, Brown University , Providence, Rhode Island , USA
7. Department of Epidemiology and International Health Institute, Brown University School of Public Health , Providence, Rhode Island , USA
8. Department of Obstetrics and Gynecology, Tufts University School of Medicine , Boston, Massachusetts , USA