From the Guidelines
Yes, the thyroid gland typically grows during pregnancy, with an increase in size of 10-20%, due to increased demands on the thyroid gland to produce more thyroid hormones, as noted in studies such as 1. The thyroid gland's growth during pregnancy is a normal physiological response to the increased demands of pregnancy. This growth is caused by the increase in estrogen levels, which leads to higher levels of thyroid-binding globulin (TBG), requiring more thyroid hormone production. Additionally, human chorionic gonadotropin (hCG), which peaks during the first trimester, has a mild stimulatory effect on the thyroid. The placenta also produces enzymes that metabolize thyroid hormones, further increasing the demand. Some key points to consider:
- The growth of the thyroid gland during pregnancy is usually not concerning and resolves after delivery, as indicated by 1.
- However, if a woman notices significant thyroid enlargement during pregnancy, she should consult her healthcare provider as it could occasionally indicate an underlying thyroid disorder that requires evaluation and possibly treatment, as suggested by 1 and 1.
- Women with hypothyroidism may need to increase their thyroid replacement dosages during pregnancy, typically by four to six weeks’ gestation, possibly by 30% or more, as noted in 1.
- Routine screening for subclinical hypothyroidism is not recommended, but women with risk factors and symptoms of thyroid diseases should be screened, and subclinical hypothyroidism should be treated, as recommended by 1.
From the Research
Thyroid Growth During Pregnancy
- The thyroid gland may increase in size during pregnancy, particularly in areas with iodine deficiency 2.
- This increase in thyroid size is thought to be due to autoregulatory mechanisms of iodine on thyroid growth, and can be partly prevented by treatment with extra iodine or thyroxine 2.
- However, in areas with sufficient iodine, thyroid size does not increase significantly during pregnancy 2.
- The physiological changes in thyroid function during pregnancy, including a slight transient increase in free thyroxine in the first trimester, may play a role in reducing energy expenditure during pregnancy 2.
- The increase in thyroid size and changes in thyroid function during pregnancy are adaptive responses to meet the increased demands for iodine and energy 2.
Factors Affecting Thyroid Function During Pregnancy
- Increased renal clearance of iodine leading to a low iodine state can affect thyroid function during pregnancy 3.
- Elevated estrogen levels can lead to an increase in circulating thyroglobulin level and a decrease in free thyroxine level, potentially affecting thyroid function 3.
- The placenta secretes compounds such as human chorionic gonadotropin (hCG), placental growth factor (PIGF), and soluble FMS-like tyrosine kinase-1 (s-Flt1) that could affect thyroid function 3.
- The passage of thyroid hormones and iodine to the fetus is highly regulated within the placental barrier, which can also impact thyroid function during pregnancy 3.