Armour thyroid is desiccated porcine extract which is a historical treatment for hypothyroidism. It contains both L-thyroxine and liothyronine. Each grain (60 mg) contains 38 μg of L-thyroxine and 9 μg liothyronine. Since the 1960s its use has been superseded by L-thyroxine. Due to limited clinical effectiveness studies, it is not licensed for use in the United Kingdom. We present a case of Armour thyroid use in pregnancy at patients request following refusal to switch to L-thyroxine.
Case: 33 year old lady was referred to our joint antenatal-endocrine clinic at 18 weeks gestation. She was initially diagnosed with primary hypothyroidism in 2010 with strongly positive TPO antibodies 6 weeks following her first pregnancy. She was commenced on 125 μg of L-thyroxine. Treatment with L-thyroxine failed to abate her symptoms and as a result she commenced a self-prescription with three grains of armour thyroid in 2011. She had a subsequent pregnancy which ended with a miscarriage at 6 weeks gestation whilst on armour thyroid. In her third pregnancy she increased her dose of armour thyroid to three and a half grains at booking. Her TSH was suppressed throughout gestation at <0.02 mU/l (0.204.00 mU/l). Her average free T4 was 12.4 pmol/l (9.019.0 pmol/l) and free T3 6.15 pmol/l (2.55.7 pmol/l). The entire course pregnancy course was uneventful with foetal normal anatomy and interval scans. She delivered a live male foetus at 40 weeks with an unremarkable baby check and heel prick screen.
Discussion: Armour thyroid is not recommended for treatment of hypothyroidism in the UK, this is more so in the context of pregnancy. There are safety concerns regarding excessive amounts of T3 relative to T4, which is inconsistent with normal physiology. In pregnancy, the potential risk to both mother and foetus are unknown. Moreover compared to L-thyroxine, it is not regarded as a pure preparation of thyroid hormone. Our patients TSH was suppressed throughout the pregnancy, despite being fully aware of the potential risks. Although the outcome was uneventful, this was an ethico-legal challenge balancing patient expectation against recommended practice. We do not recommend its use in pregnancy.