Scenario: Preconception or pregnant | Management | Hypothyroidism | CKS | NICE
Scenario: Pre-conception, pregnancy, and postpartum | Management | Hyperthyroidism | CKS | NICE
Hypothyroidism affects 3-4% of all pregnancies. If left undertreated or untreated, maternal hypothyroidism is associated with adverse foetal and maternal outcomes.
In the first 12 weeks of pregnancy, the foetus relies on the gestational parents supply of thyroid hormone, which passes through the placenta, after 12 weeks gestation, the foetus’s thyroid begins to work independently, but isn’t self-sufficient until nearer 18-20 weeks gestation.
Levothyroxine (T4) crosses the placenta and supplies the foetus’s thyroid hormone needs, in early pregnancy, T3 cannot enter the foetus’s brain, the T3 needed by the foetus is made from T4 supplied by the parent. There is limited data on the use of liothyronine available for use while pregnant, but data suggests it does not cross the placenta in significant amounts, data also does not suggest it would pose a risk of malformations to the foetus, however the risk of inadequate T4 in the foetus if the parent is treated with liothyronine means liothyronine in pregnancy is not recommended.
Levothyroxine needs during pregnancy usually increase; regular monitoring will be needed to maintain levels within pregnancy reference ranges which are different to non-pregnant reference ranges.
NHS Somerset: Medicines used in pregnancy
