Routine serum thyroid-stimulating hormone testing-optimizing pre-conception health or generating toxic knowledge?

Monitoring subclinical hypothyroidism (SCH) in women is believed to be important in terms of preventing overt hypothyroidism and optimizing the health and cognitive development of their children. Current systematic reviews have suggested an association between maternal SCH and adverse obstetric and neonatal outcomes. However, initiating the administration of thyroxine during pregnancy has failed to demonstrate appreciable health benefits. Hence there are calls by professional endocrine societies for optimizing serum thyroid-stimulating hormone (TSH) levels pre-conception. The strategy of ensuring that serum TSH levels are below 2.5 mIU/l during the pre-conception period has generated considerable uncertainty partly because the recommended level of <2.5 mIU/l is lower than those previously used to define the condition and partly due to uncertainty about the best screening programme clinicians can use in this context. Recalibrating the expected normal peri-conceptional range of serum TSH (<2.5 mIU/l), will have a significant impact on clinical services due to an inevitable increase in numbers of women diagnosed with SCH who will need to be investigated, treated and monitored. Serum TSH fulfils the criteria for a screening test and oral thyroxine is an inexpensive drug. Therefore, there is no reason to believe that screening cannot be undertaken in all women planning to conceive. Yet this approach will miss women whose pregnancies are unplanned and generate anxiety, further tests and many more prescriptions for thyroxine, coupled with the need for lifelong monitoring in affected women. A number of existing and ongoing randomized trials have evaluated the use of thyroxine in women with infertility or miscarriage with detectable thyroid auto-antibodies. These are unlikely to answer the question whether routine pre-conception testing for SCH in asymptomatic women is beneficial. Routine screening of women at risk of pregnancy and optimization of their thyroid status could result in significant health benefits for their offspring. Alternatively this approach could prove to be an expensive way of generating toxic knowledge resulting in anxiety, increased drug use and potential harm. Only large, appropriately designed studies can reveal the answer.