Environmental teratogens of man.
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Biomedical subjects
Publications and source records attributed to R W Smithells.
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Serum folate, red cell folate, white blood cell vitamin C, riboflavin saturation index, and serum vitamin A were determined during the first trimester of pregnancy in over 900 cases. For each of these there was a social classes I + II showed the highest levels which differed significantly from other classes, except for serum folate. In 6 mothers who gave birth to infants with neural tube defects, first trimester serum folate, red cell folate, white blood cell vitamin C, and riboflavin values were lower than in controls. In spite of small numbers the differences were significant for red cell folate (P less than 0-001) and white blood cell vitamin C (P less than 0-05). These findings are compatible with the hypothesis that nutritional deficiencies are significant in the causation of congenital defects of the neural tube in man.
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The incidence of congenital heart disease (C.H.D.) in Liverpool from 1960 to 1969 inclusive has been determined from the Liverpool Congenital Abnormalities Registry with a follow-up period of 3 to 12 years. The incidence is 6-6 per 1000 total births and this probably represents a very small degree of under-reporting. There is no consistent seasonal variation in the incidence of any of the main congenital heart lesions. In general, infants with C.H.D. tend to be of lower birth weight and born after shorter gestation than controls. This is most conspicuous with patent ductus arteriosus (P.D.A.). Females preponderate in P.D.A. and males in transposition. There is probably also a male preponderance in coarctation and aortic stenosis. Fallot's tetralogy is associated with increased maternal age and parity. Pregnancies leading to the birth of a baby with C.H.D. are complicated by threatened abortion more frequently than are controls. The concordance rate for C.H.D. in twins is low. Monozygotic twins are more liable to C.H.D. than are dizygotic twins. The incidence of C.H.D. in the siblings of affected propositi is 2-3 times that expected. Affected sibs often have the same lesion. About 20 per cent of infants with C.H.D. have associated major defects notably monogolism and defects of the alimentary, skeletal, genito-urinary and nervous systems. These are responsible for the early death of about one quarter of all infants born with C.H.D. The data presented here suggest that environmental rather than genetic factors are predominantly responsible for congenital heart disease.
It has been shown that women receiving oral contraceptives have increased levels of serum vitamin A. High vitamin A levels may constitute a teratogenic hazard and it has been suggested that women who conceive soon after discontinuing oral contraceptive therapy may be especially at risk to this hazard.We have confirmed a significant increase in vitamin A levels in women taking oral contraceptives. During early pregnancy there is no significant difference in vitamin A levels between women who have recently been taking oral contraceptives and those who have not. We have been unable to show that either taking oral contraceptives shortly before pregnancy or a high vitamin A level during the first trimester of pregnancy, comparable to that of a woman taking oral contraceptives, has any detrimental effect on the outcome of pregnancy. It seems unlikely that women who conceive soon after discontinuing oral contraception run any teratogenic risk from increased vitamin A levels.
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The range of defects and disabilities in thalidomide children is very much wider than is generally realized. The defects of 154 children are described and classified. Their disabilities range from incapacitating to negligible.
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