Normal Thyroid Function
The thyroid gland is controlled both indirectly and directly by the hypothalamus via thyrotropin releasing hormone (TRH) and the pituitary via thyroid stimulating hormone (TSH), respectively.(4) The thyroid gland itself, secretes thyroid hormone, which is normally found in two states, both within the gland as well as in the serum, a precursory hormone known as thyroxine (T4) as well as a metabolically active hormone, a conversion from T4, called, triiodothyronine (T3). Small amounts of T3 are released into the serum daily. Additionally, T4 is released at an approximate rate of 100-125nmol/day and has a half-life of approximately 7-10 days. Decreased production and/or serum levels of T4 levels signal increased secretion of TSH by the anterior pituitary, which, in turn, leads to hypertrophy of the thyroid gland and subsequent release of T3.(5)

Thyroid Function During Pregnancy & The Post-Partum Period
Thyroid hormone is utilized by every living cell in the body. During pregnancy, the basal metabolic rate (BMR) increases 10-25% above prepartum levels, which will affect thyroid function. Typically, T4 levels will increase but T3 levels decrease gradually until the end of the first trimester when they typically level off and become constant. Following delivery of the infant, thyroid levels return to normal by 12th week postpartum.(7) Furthermore, TSH levels are normally decreased during the first trimester of pregnancy, then normalize for the remainder, followed by a TSH surge during the first two days post-partum.(8)

Post-Partum Thyroiditis
Thyroid function is altered during pregnancy and this may lead to thyroid dysfunction, the second most common endocrine disorder during pregnancy and the postpartum period, which is prevalent amongst peripartum patients according to the following: subclinical hypothyroidism 2-3%, over hypothyroidism 0.3-0.5%, hyperthyroidism 0.1-0.4%. These disorders are frequently, but not necessarily due to autoimmune mechanisms. Those of autoimmune origin, such as Grave’s tend to improve during pregnancy due to altered maternal immune status, but may frequently be exacerbated following delivery.(9)

Postpartum thyroiditis, classified as subclinical and sometimes referred to as lymphocytic thyroiditis, is an autoimmune disease that occurs within 2-10 months following delivery in 4-10% of non-diabetic women, and in up to 25% of those who are diabetic. Additional factors that increase the risk of postpartum thyroiditis include prepartum presence of thyroid autoantibodies, iodine deficiency, and cigarette smoking.(6)

Postpartum thyroiditis typically consists of two stages, a thyrtoxic state in which there is autoimmune, lymphocyte-mediated, destruction of thyroid gland, in which the patient becomes hyperthyroid in an attempt to compensate for the destruction, and the resulting hypothyroid state due to the inability of the thyroid to resume normal function following the destruction. The thyrotoxic state is not necessary to cause postpartum hypothyroidism, nor is it required to make a diagnosis of postpartum thyroiditis.

Patients who have postpartum thyroiditis may present with non-tender thyroid enlargement and/or the following symptoms: lack of sleep, nervousness, fatigue, and easy weight loss. (6)

Serum tests for postpartum hyperthyroidism are characterized by low TSH and high free T4 levels, while postpartum hypothyroidism would be characterized by opposite findings, high TSH and low free T3 and T4 levels. (2) Additionally, high antithyroid antibody titers may be present.(1)

Although frequently self-limiting and resolves within two to four months of its onset, in some cases, postpartum thyroiditis can lead to permanent hypothyroidism due to the pathological destruction of the thyroid gland which occurs while the disorder is active. Allopathic (traditional medicine) management of this condition includes the oral administration of T4 until the thyroid and TSH levels return to normal for those with hypothyroidism, and beta-blockers for those who have hyperthyroidism.

Significance:
1] Thyroid disorders during pregnancy post a threat to maternal health as well as the viability of the fetus in question, as well as the integrity of future pregnancies. (6)

2] Thyroid disorders may cause signs and symptoms that are musculoskeletal in nature and therefore subclinical cases may be overlooked. Furthermore, some of these symptoms may too often be dismissed as part of normal and expected findings during the postpartum period. (6) As a reminder, some of the most common symptoms and signs of hypothyroidism and hyperthyroidism are listed below:

Hypothyroidism
Symptoms of hypothyroidism include: fatigue, loss of energy, and/or lethargy, weight gain; decreased appetite; cold intolerance; dry skin and decreased perspiration; hair loss; sleepiness; muscle pain, joint pain, and/or weakness in the extremities; paresthesia and/or nerve entrapment syndromes; depression; mental impairment such as forgetfulness, impaired memory or inability to concentrate; blurred vision; hearing loss; fullness or hoarseness in the throat region; constipation; as well as infertility and/or menstrual irregularities. (5)

Physical signs of hypothyroidism include the following: hypothermia; weight gain; lethargy in speech and movement; pallor and dullness of facial expression; coarsened facial expressions; brittle, straw like hair; loss of scalp, axillary, and/or pubic hair; hoarseness, goiter, or macroglossia; periorbial puffiness, abdominal distension, myxedema, and/or pitting edema; bradycardia, decreased systolic with increased diastolic blood pressure, pericardial effusion; and hyporeflexia with delayed relaxation, ataxia, bothHyperthyroidism
Common symptoms of hyperthyroidism include the following: nervousness, anxiety, increased perspiration, heat intolerance, tremor, hyperactivity, palpitations, weight loss despite increased appetite, and reduction in menstrual flow or oligomenorrhea. Common signs of hyperthyroidism include the following: hyperactivity, tachycardia or atrial arrhythmia, systolic hypertension, warm, moist, and smooth skin, lid lag, stare, tremor, and muscle weakness. (10)

3] Increased risk towards comorbid conditions and future health problems: Decreased thyroid hormone effect can cause increased levels of total cholesterol and low-density lipoprotein (LDL) cholesterol and a possible change in high-density lipoprotein (HDL) cholesterol due to a change in metabolic clearance. In addition, hypothyroidism may result in an increase in insulin resistance.

4] There is a correlation between hypothyroidism and post partum depression.

Differential Diagnosis/Other Problems to Consider:
Prolactin Deficiency, Pituitary Adenoma (5), Disturbance of the Hypothalamus

References:
1] http://emedicine.medscape.com/article/125648-overview
2] http://www.medscape.com/viewarticle/433853_5
3] http://www.aafp.org/afp/20020201/431.html
4] Medical Physiology. Guyton & Hall.
5] http://emedicine.medscape.com/article/122393-overview
6] http://emedicine.medscape.com/article/125648-overview
7] Interpretation of diagnostic tests: A handbook of laboratory medicine. Wallach J. 1970.
8] Interpretation of diagnostic tests. Wallach J. 6th ed. 1996.
9] http://emedicine.medscape.com/article/261913-overview
10] http://emedicine.medscape.com/article/121865-overview

This article was originally published by Dr. Bergan-Guzman, in the Synapse a publication of National University of Health Sciences. Volume 32:1. Healing. Septemer/October 2009.