Thyroid Disease During Pregnancy

Options for Management

Tuija Männistö


Expert Rev Endocrinol Metab. 2013;8(6):537-547. 

In This Article

Autoimmune Thyroiditis & Postpartum Thyroiditis

Approximately 11–15% of all fertile aged women have positive thyroid antibodies, either thyroid peroxidase antibodies (TPO-Abs) or thyroglobulin antibodies (TG-Ab), which act as a marker of silent autoimmune thyroiditis. Up to 20–40% of all women with positive thyroid antibodies develop hypothyroidism during pregnancy or immediately postpartum,[46,74] and generally women with autoimmune thyroiditis have higher TSH concentrations at baseline.[46] Notably, TPO-Ab and TG-Ab concentrations decrease as pregnancy progresses,[46] so false-negative findings regarding thyroid autoimmunity are possible in late gestation.

Thyroid antibody positivity has been associated with increased risk for miscarriages,[75–78] perinatal mortality[35] and preterm birth.[77] TPO-Ab positivity in euthyroid women is associated with placental abruptions,[79] very early preterm delivery,[80] neonatal respiratory distress[80] and externalizing problems, for example, attention problems and aggressive behavior, in children.[81] However, most of these studies evaluated thyroid function only once during pregnancy, so the effect of hypothyroidism as the underlying reason for these associations cannot be ruled out.

The effect of levothyroxine treatment among TPO-Ab-positive euthyroid women to reduce miscarriages has been studied in a few trials, with generally encouraging results.[74,75] In one trial, risk for preterm delivery risk was also reduced.[74] Among women undergoing in vitro fertilization, the pregnancy and delivery rates of TPO-Ab-positive and -negative women are generally similar[78] and levothyroxine treatment of TPO-Ab-positive women did not improve delivery outcomes.[78] However, women undergoing assisted reproduction with TPO-Ab positivity and miscarriage had higher prepregnancy TSH than those with successful pregnancies.[82] Overall, these studies suggest that the association between TPO-Ab positivity and adverse outcomes might be influenced by the presence of hypothyroidism, so levothyroxine might be improving pregnancy outcomes by addressing hypothyroidism rather than a direct effect related to antibody status. More studies with longitudinal follow-up are needed to demonstrate whether thyroid autoimmunity is associated with adverse outcomes in women who are euthyroid throughout pregnancy.

In one small trial among women with autoimmune thyroiditis undergoing ovulation stimulation and intrauterine insemination, oral prednisone treatment was associated with somewhat improved pregnancy rates but no difference in miscarriages.[83] However, until these results are replicated in other studies and in women with thyroid autoimmunity trying to conceive spontaneously, prednisone treatment cannot be recommended.

Postpartum thyroiditis is a new-onset thyroid dysfunction during the 12 months following pregnancy in a previously euthyroid woman.[2] The risk of postpartum thyroiditis is higher in women with positive thyroid antibodies or other autoimmune diseases.[2,84] Up to 50% of all women with TPO-Ab or TG-Ab positivity in the first trimester of pregnancy develop postpartum thyroiditis.[2,84] In its classical form, postpartum thyroiditis manifests with an episode of thyrotoxicosis followed by transient hypothyroidism and subsequent euthyroidism, but the clinical course varies.[2,84] The thyrotoxic phase generally does not require or respond to antithyroid drugs but symptomatic women may be treated with a low dose of propranolol. Treatment of the hypothyroid phase of postpartum thyroiditis with levothyroxine depends on the symptom severity, if a woman is breastfeeding, if she plans to conceive again in the near future and her preference to receive treatment.[2,84] Treatment for postpartum thyroiditis is usually transient, with discontinuation of treatment 6–12 months after the initiation, unless the patient is pregnant, breastfeeding or trying to become pregnant.[2,84] Postpartum thyroiditis can lead to permanent hypothyroidism in over 50% of all women and annual TSH tests are indicated to those with postpartum thyroiditis history.[2,84]