1. Annotated Bibliography on Maternal Nutrition (1970 ): U.S. Department of Health, Education, and Welfare, Washington, p70 .
2. Reduction of Incidence of Prematurity by Folic Acid Supplementation in Pregnancy
3. N. R. Butler, and D. G. Bonham (1963 ): PerinataI Mortality . First Report of the 1958 British Perinatal Mortality Survey. Livingstone, Edinburgh, p71 .
4. N. R. Butler, and E. D. Alberman (1969 ): Perinatal Problems . Second Report of the 1958 British Perinatal Mortality Survey. E. & S. Livingstone Ltd, Edinburgh and London, p41 .