Wald, N.J.; Brock, D.J.H.; Bonnar, J. (1974). "Prenatal Diagnosis of Spina Bifida and Anencephaly by Maternal Serum-Alpha-Fetoprotein Measurement". The Lancet. 303 (7861): 765–767. doi:10.1016/S0140-6736(74)92838-4. PMID4132705.
Wald, NJ; Densem, J; Frost, C; Stone, R (20 July 1991). "Prevention of neural tube defects: Results of the Medical Research Council Vitamin Study". The Lancet. 338 (8760): 131–137. doi:10.1016/0140-6736(91)90133-A.
Wald, N.J.; Brock, D.J.H.; Bonnar, J. (1974). "Prenatal Diagnosis of Spina Bifida and Anencephaly by Maternal Serum-Alpha-Fetoprotein Measurement". The Lancet. 303 (7861): 765–767. doi:10.1016/S0140-6736(74)92838-4. PMID4132705.