Hyperthyroidism and Pregnancy
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
At first when I started to write on this topic, I thought of my rotation through Obstetrics as a medical student. I particularly remember one patient during my first week who had Graves' disease and presented to the hospital in her 6th month of pregnancy with uncontrolled hyperthyroidism (overactive thyroid). The attending doctor's face was stern and serious as he went around the table and asked us why we should be concerned. This article will discuss hyperthyroidism in pregnancy and its effects on both the mother and child.
During pregnancy, the hormone HCG (human chorionic gonadotropin) is produced. HCG is the hormone that "pregnancy tests" detect. HCG increases to a peak at around 12 weeks. It has mild thyroid stimulating effects and, as a result, can cause some symptoms of hyperthyroidism. HCG is in part responsible for the nausea during the first trimester. In situations of multiple pregnancies (twins, triplets) HCG levels are even higher, and symptoms can be more pronounced. Temporary subclinical (no apparent symptoms) hyperthyroidism occurs in 10-20% of normal pregnant women during this period, and these women typically do not require treatment.
Hyperemesis gravidarum is a syndrome of nausea and vomiting that is associated with weight loss of more than 5% during early pregnancy. It is associated with high levels of HCG. Sixty percent of these women have either subclinical (no apparent symptoms) or mildly clinical (mild symptoms) hyperthyroidism, which also usually resolves after the first trimester.