During pregnancy, a number of changes occur in the mother’s thyroid function. Human chorionic gonadotropin (HCg), a glycoprotein produced by the placenta has a stimulating action on the mother’s thyroid gland leading to increased thyroid hormone production (T3 & T4) as well as partial suppression of TSH, putting mum into more of a temporary hyperthyroid state. For this reason, it is important to know that ranges for thyroid function change in pregnancy compared to non pregnant ranges, so ensure the pregnancy ranges are being applied if you are pregnant and having your bloods done.
Until further data is available and as of 2018, the following trimester-specific recommendations for TSH reference ranges during pregnancy are:
0.1–2.5 mIU/L (first trimester),
0.2–0.3 mIU/L (second trimester), and
0.3–3.0 mIU/L (third trimester)1
Note these ranges are quite different to non-pregnant ranges, thus it is important to routinely check thyroid hormones at every trimester if you have a thyroid condition such as Hashimotos or Graves disease as having enough thyroid hormones, in particular T3, is imperative for the development of the baby, especially during the first trimester of pregnancy, when the fetal thyroid gland is not fully functional.
Baby is dependant on mum having adequate amounts as the mother’s thyroid hormones cross the placenta in small quantities to maintain normal fetal thyroid function and thus inadequate T3 is associated with increased risk of miscarriage as well as developmental issues to the baby.
Adequate nutrients (e.g. iodine, selenium, zinc, iron, tyrosine, vitamin A, vitamin D) are all essential to make thyroid hormones however pregnancy increases demands of pretty much all these nutrients.
Naturopathic management ensures there are adequate intake of these nutrients in the diet as well as proper absorption of these nutrients to ensure optimal levels of T3 and reduce autoimmune risk.
1. Leung AM1 Thyroid function in pregnancy J Trace Elem Med Biol. 2012 Jun;26(2-3):137-40