Postpartum hypothyroidism

Pituitary failure (secondary hypothyroidism) is an uncommon cause resulting from pituitary tumors, surgical therapy, external pituitary radiation, postpartum pituitary necrosis, metastatic tumors, tuberculosis, histiocytosis, and autoimmune mechanisms. 

Secondary hypothyroidism, or pituitary hypothyroidism, is the consequence of impaired thyroid-stimulating hormone (TSH) secretion and is less common than primary hypothyroidism. It may result from any of the causes of hypopituitarism (e.g., pituitary tumor, postpartum pituitary necrosis, trauma). Patients with secondary hypothyroidism exhibit undetectable or inappropriately low serum TSH concentrations. In secondary hypothyroidism, a normal thyroid gland lacks the normal level of TSH stimulation necessary to synthesize and secrete thyroid hormones. Such patients usually also have impaired secretion of TSH in response to exogenous thyrotropin-releasing hormone (TRH) administration. 

Thyroid Hypofunction Hypothyroidism is the most common disorder of thyroid function. It can be divided into patients who have a failure of the thyroid gland to produce sufficient thyroid hormone (primary hypothyroidism) and patients in which pituitary or hypothalamic disease is associated with impaired TSH stimulation (central or secondary hypothyroidism). Worldwide, primary hypothyroidism is caused most often by iodine deficiency. In areas where iodine is sufficient, chronic autoimmune thyroiditis (Hashimoto s thyroiditis) accounts for most cases. Other causes include postpartum thyroiditis, surgical removal, or radioactive iodine ablation of the gland. Hypothyroidism present at birth (cretinism) is the most common preventable cause of mental retardation in the world. 

Women who have recendy been pregnant comprise an important subpopulation that is frequendy studied to elucidate the prevalence of hypothyroidism. While there are no large population-based reports to date, there are considerable data on the frequency of hypothyroidism in relatively small groups of patients. Postpartum lymphocytic thyroiditis results in transient hypothyroidism, with up to one quarter of patients eventually becoming permanently... 

Hypothyroidism thus remains a significant source of morbidity in the American population. Within this iodine-replete population, relatively small differences in iodine intake do not appear to significantly affect the prevalence of this disorder. Although the risk of hypothyroidism associated with postpartum thyroiditis is significant, the most important subpopulation at risk for hypothyroidism appears to be the elderly. 

Postpartum thyroiditis with hypothyroidism occurs after 6—9% of pregnancies in the United States. 

The most common causes of central hypothyroidism are pituitary adenomas, craniopharyngiomas and the surgery and/or radiotherapy used to treat them. Central hypothyroidism can also result from other tumors (i.e., glioma, meningioma, chordoma, etc.), from a number of inffltra-tive conditions, such as sarcoidosis and histiocytosis, and from postpartum necrosis (Sheehans syndrome). 

Several studies have shown that, when hypothyroid women become pregnant and maintain the pregnancy, they carry an increased risk for obstetric complications. Greater risk of abortion, anemia, gestation hypertension (including severe forms of eclampsia and preeclampsia), abrupto placentae and postpartum hemorrhage have been described (Table 113.2). 

After delivery, most hypothyroid women need the L-T4 dosage they received during pregnancy to be decreased to the preconception dosage. TSH level should be rechecked at 6 weeks postpartum, and it is important to continue monitoring TFTs for at least 6 months after dehvery. 

Within a year of giving birth, 5 to 10 percent of women develop hypothyroidism secondary to postpartum thyroiditis. Initially, thyroid hormone levels may rise, then either return to normal or drop to hypothyroid levels. Of those women who become hypothyroid, about 20 percent will require lifelong treatmenL... 

Roti, E., Minelli, R., Gardini, E., Bianconi, L., Neri, T., Gavaruzzi, G., Ugolotti, G., Salvo, D., Braverman, L.E., Impaired intrathyroidal iodine organificaton and iodine-induced hypothyroidism in euthyroid women with a previous episode of postpartum thyroiditis, J. Clin. Endocrinol. Metab. 73 958 (1991). 

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