To the Editor:
We have just read a publication by Bernardi et al. on the topic of subclinical hypothyroidism and recurrent early pregnancy loss (1). Going through the paper we found that the opposite situation was being described, that is, no impact of subclinical hypothyroidism on recurrent early pregnancy loss. This puzzling situation motivated us to dissect the concepts presented by the authors.
One central point of misconception on thyroid function can be tracked down to a 2007 publication cited by Bernardi which recommended a “desirable TSH level” of 2.5 mIU/ml for pregnant women. In that original publication the authors had admitted that this recommendation was done on the basis of a poor level of evidence. Although this recommendation does not fulfill the principles of evidence-based medicine, it has very unfortunately found its way into clinical practice. Choosing a low cut-off value for the upper range of TSH, as Bernardi et al. have done, will result in a misclassification of normal subjects by which the apparent subgroups, euthyroids and women with subclinical hypothyroidism, are not truly subgroups but belong to a same group of subjects having TSH values within the normal range. Therefore it is logical that one cannot expect to find any difference between these artificial subgroups in relation to recurrent early pregnancy loss. Read the rest of this entry »