According to the 2011 "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum," research has shown that women who are positive for thyroid antibodies -– thyroid peroxidase (TPOAb), thyroglobulin (TgAb), or anti-microsomal antibodies -- have a risk of pregnancy loss that is two to four times higher than the normal population of women. While there is a clear link, it’s not clear whether the elevated antibody levels are actually the cause of the pregnancy loss, however.
The Guidelines point to a study that showed a significantly decreased rate of pregnancy loss in women who were TPOAb-positive and treated with levothyroxine, versus untreated (3.5% vs. 13.8%). The Guidelines, however, stated that there is insufficient evidence to recommend for or against screening all women for thyroid antibodies in the first trimester of pregnancy.
Recurrent Pregnancy Loss and Thyroid AntibodiesRecurrent pregnancy loss –- which occurs in about 1% of women –- is defined as two consecutive pregnancy losses, or three total spontaneous losses.
Some studies have found a higher prevalence of thyroid antibodies in women who have had recurrent pregnancy loss, while other studies have not found a connection. There is, however, some evidence that anti-phospholipid antibodies and thyroid antibodies may interact to cause pregnancy loss in some women.
In women with recurrent pregnancy loss, trials with intravenous immunoglobulin (IVIG) or levothyroxine have shown a decrease in the rate of pregnancy loss. The Guidelines say that the studies demonstrating this connection have methodological problems, however, and so they feel there is not enough evidence to recommend for or against antibody screening, or levothyroxine or IVIG treatment to help prevent recurrent pregnancy loss.
Thyroid Antibodies, Pregnancy Loss and In-Vitro Fertilization (IVF)Studies are mixed as to the relationship between thyroid antibodies and pregnancy loss in women undergoing in-vitro fertilization (IVF). The Guidelines state that there is not enough evidence to recommend for or against levothyroxine treatment in women who have thyroid antibodies, but who have normal thyroid levels, and are undergoing assisted reproduction.
Preterm Delivery in Women with Thyroid Antibodies and Normal Thyroid LevelsPreterm delivery -– which is considered birth prior to 37 weeks gestation -– occurs in approximately 12% of pregnancies in the U.S., and is the leading cause of neonatal death, and the second leading cause of death in newborns. Uncontrolled hyperthyroidism results in a higher rate of preterm delivery, and studies have shown that women who are positive for thyroid peroxidase and/or thyroglobulin antibody have a higher rate of preterm birth.
Because research results were mixed, the Guidelines state that there is not enough evidence to recommend for or against screening for thyroid antibodies in the first trimester of pregnancy, or treating thyroid antibody-positive women who have normal thyroid levels, to prevent preterm delivery.
One study has shown, however, that thyroid peroxidase antibody-positive women who were treated with levothyroxine had a significantly lower rate of preterm delivery (7%) compared to women who were not treated (22.4%).
Stagnaro-Green, Alex, et. al. "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum.” Thyroid. Volume 21, Number 10, 2011 (Online)