1. Tropical Medicine Research Institute (M.S.B., R.A.F., M.R., T.E.F.), University of the West Indies, Mona, Kingston 7, Jamaica
2. Department of Obstetrics, Gynaecology, and Child Health (M.T., L.G.), University of the West Indies, Mona, Kingston 7, Jamaica
3. Medical Research Council Epidemiology Resource Centre (C.O.), University of Southampton, Southampton SO16 6YD, United Kingdom