If a test during pregnancy reveals low free thyroxine, it is possible that the pregnant woman is suffering from hypothyroidism. There are many changes in hormone levels in the body after pregnancy, and these hormones may affect the secretion of thyroxine and even cause hypothyroidism to occur. Thyroid hormones can promote the biological metabolism of sugar, protein, fat and other substances, as well as the synthesis of protein, which is a raw material substance necessary for fetal growth and development. If free thyroid hormone is low after pregnancy, there is a risk of miscarriage, fetal malformation, fetal growth restriction or fetal growth retardation. Therefore, if you have a low free thyroxine test, it is recommended that you take the necessary medication in combination with other laboratory tests.