[1] North Middlesex Univ Hosp, Obstet & Gynaecol, London, England
[2] Lagos Univ Teaching Hosp, Obstet & Gynaecol, Lagos, Nigeria
[3] Lagos Univ Teaching Hosp, Obstet & Gyanecol, Coll Med, Lagos, Nigeria
[4] Univ Witwatersrand, Div Epidemiol & Biostat, Johannesburg, South Africa