November 7, 2017

expert reaction to unpublished conference abstract on pregnant women’s exposure to the chemical perchlorate and maternal thyroid hormone levels

Research presented at the Society for Endocrinology Annual Conference, examines whether pregnant women exposed to higher levels of a common environmental pollutant – perchlorate – had lower levels of a thyroid hormone crucial for normal foetal brain development.

Dr Mark Vanderpump, Consultant Physician and Endocrinologist & member of the Society for Endocrinology, said:

“Thyroid hormone, requiring adequate maternal iodine intake, is critical for foetal neurodevelopment. Perchlorate is used in a variety of industrial products including missile fuel, fireworks and fertilisers and blocks thyroid iodine uptake. Previous studies investigating perchlorate exposure have been limited by small sample sizes and short study duration but have not demonstrated that environmental perchlorate exposure adversely affects thyroid function in pregnant women. This epidemiological study in UK pregnant women has demonstrated an association between evidence of perchlorate exposure and subtle low circulating thyroid hormone levels in the third trimester. Further study is required to establish whether this exposure is associated with neurodevelopment abnormalities in children.”

Dr Michelle Bellingham, Lecturer at the Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow & member of the Society for Endocrinology, said:

“I think it is a very tenuous link to infer that a reduction in concentrations of maternal thyroid hormones in third trimester urine and blood could potentially be associated with neurodevelopmental problems in foetus. There are several endogenous (and exogenous) factors, in addition to T4, which are also crucially involved in programming normal brain development (not measured in the study), therefore to pull out an association between one chemical and T4 and then speculate that exposure to this common chemical could cause neurodevelopmental disorders in offspring, I am concerned about how this might be received by the public.

“Personally I feel there is not enough information in the abstract to be able to draw such a conclusion. To begin with it’s not clear how many samples were taken e.g. was this a one-time sample point? In which case it only reflects the T4 level at that time and is not reflective of T4 levels across gestation. Brain development occurs throughout gestation and so a one-time measurement in the third trimester does not indicate what the levels of either the chemical or T4 were like during other critical windows of development. Nor is it clear whether the mother’s occupation or diet could be confounders or whether this was taken into account in the analysis. It comes down to the well know saying that correlation cannot infer causation and based on the minimal information given in the abstract pregnant women should not be panicked by this finding. There is minimal detail on the method of sample analysis which is important. Also maternal blood and urine concentrations cannot be directly related to what the developing foetus is exposed to; the authors do not know the levels in the developing foetus which also makes it difficult to speculate about the effects on the developing brain.”

* ‘Perchlorate exposure affects thyroid function in third trimester pregnant women from South-West England’ by Knight et al. presented at the Society for Endocrinology Annual Conference on Tuesday 7 November.

Declared interests

Dr Mark Vanderpump: No conflicts of interest

None others received.