BMJ 1996;312:580 (2 March)

Letters

Predictors of neonatal encephalopathy in full term infants

More information needed about possible role of thyroxine

EDITOR,--Stuart J Adamson and colleagues suggest that maternal thyroxine treatment increases the risk of neonatal encephalopathy, with an odds ratio of between 1.2 and infinity (the mothers of six of the affected babies were taking thyroxine, compared with none of the mothers of the control babies).1 They also claim that this is biologically plausible. These statements need further qualification in view of the large numbers of women who take thyroxine in pregnancy (approaching 1% in our population).

Do the authors claim that the maternal thyroxine treatment itself is dangerous? The fetal thyroid begins to function independently of the maternal hypopituitary-thyroid axis late in the first trimester and is not affected by either maternal thyroxine or thyroid stimulating hormone.2 More importantly, little if any maternal thyroxine is able to cross the placenta.3 Even large doses of thyroxine taken to suppress thyroid cancer do . . . [Full text of this article]


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Relevant Article

Predictors of neonatal encephalopathy in full term infants
Stuart J Adamson, Louisa M Alessandri, Nadia Badawi, Paul R Burton, Patrick J Pemberton, and Fiona Stanley
BMJ 1995 311: 598-602. [Abstract] [Full Text]

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