1. Birth counts: Statistics ofpregnancy and childbirth;for example, See; A, Macfarlane; M, Mugford,1984
2. Population Censuses and Surveys. Occupational mortality. The Registrar General Decennial Supplement for England and Wales 1970-1972 Series;p'82.;DS,1978
3. The Aberdeen maternity and neonatal data bank, in Mednick SA;Samphier, M.L.; Thompson, B.
4. Prospective longitudinal research,1981
5. The Cardiff Births Survey: development, perinatal mortality, birthweight and length of gestation;Andrews, J.; Davies, K.; Chalmers, I.; Campbell, H.