Pregnant women overdiagnosed and treated for thyroid dysfunction

‘The practice of TSH [thyroid stimulating hormone] testing early in the first trimester may be resulting in overdiagnosis and unnecessary thyroid hormone therapy during and after pregnancy.’
 
That is endocrinologist Dr Lois Donovan, co-author of new research published in the Canadian Medical Association Journal (CMAJ).
 
The retrospective cohort study followed more than 188,000 pregnancies in Alberta, Canada. It found that more than 111,000 of those pregnant women (59.2%) had at least one TSH measurement performed, usually around gestation week five to six.
 
In 5050 pregnancies (4.5%), women were started on thyroid hormone therapy. Almost half of these women (44.6%) continued treatment after giving birth, and almost one-third (31.5%) received two or more prescriptions in the first postpartum year.
 
‘This raises concerns about overmedicalisation during pregnancy, given that minor, untreated TSH elevation usually normalised, as indicated by repeat measurement,’ the authors said.
 
‘The frequent postpartum continuation of thyroid hormone therapy for those who started it during pregnancy adds to this concern.’
 
Dr Alex Polyakov is a senior lecturer in the Department of Obstetrics and Gynaecology at the University of Melbourne and a consultant obstetrician, gynaecologist and fertility specialist at the Reproductive Biology Unit at the Royal Women’s Hospital in Melbourne.
 
He told newsGP the same issues are happening in Australia.
 
‘A lot of doctors do thyroid function testing – so, TSH in their initial blood tests when someone becomes pregnant – but the recommendation is not to test universally,’ he said.
 
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) outlines current Australian recommendations in their position statement on hypothyroidism in pregnancy.
 
According to that statement, thyroid function testing should only be performed on pregnant women who have symptoms of thyroid disease or are at risk of, or have a personal history of, thyroid dysfunction.
 
RANZCOG states that screening for sub-clinical hypothyroidism and subsequent treatment with thyroxine is not recommended in pregnancy.
 
Yet, Dr Polyakov said, TSH is often added on to pre-pregnancy screening blood tests. When that happens, he cautions that results need to be interpreted in the context of pregnancy, as the reference range for TSH is a ‘little bit lower’ than normal in the first trimester.
 
‘So if the other parameters, like T3 and T4 are normal, most women actually don’t require treatment,’ Dr Polyakov said.
 
‘There is no evidence, or very poor evidence, that it improves pregnancy outcomes if you treat sub-clinical hypothyroidism.’
 
On the other hand, treating pregnant women who are overtly hypothyroid is important.
 
Dr Polyakov said clinical hypothyroidism in pregnancy can lead to a host of negative effects, including increased risk of placental abruption, neurodevelopmental delay in children, miscarriage, pre-eclampsia, low birth weight and perinatal mortality.
 
However, he said these risks are only for women who have overt – not sub-clinical – hypothyroidism.
 
‘That has to be quite severe; we’re talking about TSH above 10, or TSH above reference range with abnormal T4,’ he said.
 
Instead of adhering to such guidelines, Dr Polyakov said pregnant women who yield an ‘even slightly abnormal’ TSH result are often commenced on thyroxine.
 
‘Then nobody tests again, almost ever, and patients just continue taking it long-term, even after delivery without any further testing, which is really not appropriate,’ he said.
 
‘Most of these people don’t really require long-term therapy.
 
‘It’s not detrimental; it’s just not very useful.’
 
If a woman is commenced on treatment for hypothyroidism during pregnancy, Dr Polyakov said it is important to continue testing thyroid function.
 
‘They should have thyroid function tested in every trimester and then it should be tested again six weeks after they deliver to determine whether they should require continuation of therapy,’ he said.
 
‘That does not seem to be happening, certainly in Canada, and I think in Australia it’s a similar picture.’
 
While Dr Polyakov said overdiagnosis of thyroid dysfunction is problematic, he said lack of long-term follow-up is the most worrying concern.
 
‘The problem that this study identified is not so much that people test and then treat hypothyroidism – because there is no adverse outcome in someone who is treated for sub-clinical hypothyroidism – the problem is that a lot of those people continue taking thyroxine long-term, even after pregnancy and for most of them it is really not required,’ he said.
 
‘So there is a lot of overtreatment.’
 
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