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Thyroid problems can be at the root of miscarriage and premature birth

Posted May 10 2011 9:54am

In conventional medicine it is my experience that we tend to struggle a bit with the diagnosis and management of certain conditions, and near the top of the list (again, in my experience) is low thyroid function (hypothyroidism). Conventional wisdom dictates that ‘normal’ levels of thyroid hormones mean normal thyroid function. The ‘screening’ test for thyroid function is to measure ‘thyroid stimulating hormone’ (TSH). Raised levels of this point to low thyroid function. However, there is evidence that TSH is not as utterly reliable as an indicator of thyroid function or marker of health, and I’ve written previously about some of the issues here , here and here .

I’ve known for a long time that, in practice, it’s wise to assess individuals biochemically, but at the same time it’s crucial to take into account the clinical picture too. Failure to do this, in my view, can result in individuals suffering needlessly. And the symptoms of hypothyroidism are not just a minor inconvenience either. They can include: weight gain, fatigue, low mood and depression, mental lethargy, generalised swelling (known as ‘myxoedema’), sensitivity to cold, dry skin, dry hair, thinning of the hair and constipation. It’s unusual for hypothyroid individuals to exhibit all these symptoms, but it’s not uncommon for them to exhibit many of them.

In more recent times, I’ve become increasingly aware that it’s generally a good idea to check levels of ‘thyroid auto-antibodies’. These antibodies are made by the body in response to substances involved in thyroid function. The two most commonly tested antibodies when hypothyroidism is being suspected are anti thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-TG). I think it’s fair to say that most endocrinologists (hormone disorder specialists) would not treat a person with positive antibodies who also has a normal TSH level. However, I doubt that this is the best way, particularly having read this book . The book focuses on the most common form of hypothyoidism known as ‘Hashimoto’s Disease’. One may point made by the book as that standard blood tests are not to be relied upon. It also recommends management of the immune dysfunction that appears to be at the root of the disease. One key strategy here is to avoid gluten (in foods such as wheat, oats, rye and barley). For more details, see the book!

The relevance of thyroid antibodies was again highlighted this week on the publication of a study in the British Medical Journal [1]. In this review, the relationship between thyroid autoantibodies and miscarriage and preterm (premature) birth was assessed. Pre-term birth was defined, in this review, as birth occurring from between 24 and 37 weeks gestation.

Here’s a summary of the findings of this review:

1.     Evidence from ‘cohort’ studies (generally recognised as the best type of ‘epidemiological’ evidence) showed that the presence of thyroid autoantibodies was associated with a 390 per cent increased risk of miscarriage (i.e. risk was almost 4 times that in individuals without antibodies).

2.     Evidence from ‘case-control’ studies (generally regarded as inferior to cohort studies) risk of miscarriage was raised by 80 per cent in individuals with thyroid autoantibodies).

3.     The presence of autoantibodies was associated with a more than doubling in risk of pre-term birth.

The authors of the review offer two potential explanations for how a positive antibody status might affect pregnancy:

Firstly, the presence of thyroid autoantibodies in women with normal thyroid function could be associated with a subtle deficiency in the availability of thyroid hormones (a fall in circulating free thyroid hormones within the reference range) or a lower capacity of the thyroid gland to adequately rise to the demand for augmented synthesis of thyroid hormones required in pregnancy. Given that minor perturbations in thyroxine concentrations within the normal range can lead to an association between thyroid autoantibodies and adverse pregnancy outcomes, trials have been conducted to evaluate the effects of supplementation with levothyroxine on pregnancy outcomes in women with normal thyroid function who tested positive for thyroid autoantibodies. Secondly, thyroid autoantibodies might be an indicator of an underlying enhanced global autoimmune state. This itself can have a direct adverse effect on placental or fetal development.

Notice here there is mention of treating those with positive antibodies with levothyroxine (the stand drug/hormone used to treat hypothyroidism). The review goes on to report on the results of these trials: overall, treatment with levothyroxine roughly halves the risk of miscarriage.

Of what use is all this information? If you or someone you know has had a miscarriage or pre-term delivery (or perhaps more than one) and is planning pregnancy (however far off this may be), I suggest having a full thyroid ‘work-up’ including levels of TSH, free T4 and free T3. I recommend, obviously, that thyroid autoantibodies be checked too.

If your doctor expresses scepticism regarding the need for these tests, show him or her the study I’m reporting here. Click this link for a full text version of it.

In Malta recently I suggested that someone have her antibodies checked as I suspected hypothyroidism. The lab refused to do the test. Why? Because the TSH was normal. The problem, as I see it, is that people who work in labs generally haven’t seen enough patients, and don’t appreciate just how limited in value the TSH test is in practice.

References:

1. Thangaratinam S, et al. Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence. BMJ 2011; 342:d261

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