In addition to this post, please see 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum. Alexander, Pearce, et al., Thyroid. March 2017, 27(3): 315-389. doi:10.1089/thy.2016.0457.
In this post I link to and excerpt from the section on Pregnancy and Hypothyroidism from the Curbsiders‘ [Link is to the Full Episode List] #208 Hypothyroidism Master Class with Susan Mandel MD, MPH. APRIL 20, 2020 By DR. ELENA GIBSON.
Here is the excerpt:
Pregnancy and Hypothyroidism
When a woman is diagnosed with hypothyroidism, Dr. Mandel recommends immediate counseling on the importance of thyroid hormone adjustment before and during pregnancy. Additional levothyroxine is needed during pregnancy, and dose adjustments could be necessary as early as 6 weeks (Mandel 1990). Fetal development relies on maternal T4 during the first trimester, so patients should let a provider know as soon as possible instead of waiting until the first trimester appointment (usually around 11-12 weeks) (Patel 2011). Required levothyroxine dose increases vary from approximately 25-40% based on how much functioning thyroid the mother has left, with higher dose adjustments required for surgical hypothyroidism compared to autoimmune (Jonklaas 2014). Until a pregnant patient is able to have thyroid function testing completed, Dr. Mandel will often recommend taking 2 extra pills per week to avoid low thyroxine levels. Furthermore, remind patients to take their prenatal vitamin and levothyroxine at different times to avoid decreased levothyroxine absorption. Postpartum, dosing should return to the same dose before pregnancy and there are no changes required while breastfeeding (Garber 2012).
Kashlak Pearl: Fetal development relies on maternal T4 during the first trimester. Therefore, until a pregnant patient is able to have thyroid function testing completed, Dr. Mandel recommends taking 2 extra pills per week to avoid low thyroxine levels.