1. Department of Obstetrics and Gynaecology, Federal Medical Centre, Makurdi, Nigeria;
2. Federal Ministry of Health, Abuja, Nigeria;
3. Nigeria Field Epidemiology and Laboratory Training Programme/African Field Epidemiology Network, Abuja, Nigeria;
4. Department of Epidemiology and Medical Statistics, University of Ibadan, Ibadan, Nigeria;
5. Department of Obstetrics and Gynaecology, University of Maiduguri, Maiduguri, Nigeria