Chapter 22: Endocrine Disorders in Pregnancy

INTRODUCTION

Pregnancy results in multiple normal physiologic changes, and these changes may have an impact on the diagnosis, evaluation, or treatment of endocrine disorders. Pregnancy itself is the result of, and maintained by, a well-choreographed set of endocrine signaling. Ovulation results from the orchestration of signaling from the hypothalamus, pituitary, ovary, and uterus axis. Pregnancy occurs when the ovulated egg is fertilized and implants in the previously prepared endometrium. Pregnancy continues through the first half of the first trimester dependent on the corpus luteum. The rest of pregnancy is maintained by placental hormonal support.

A clinical challenge occurs in the diagnosis and treatment of endocrine disorders during pregnancy because many of the symptoms of the endocrine diseases are common symptoms in pregnancy. Physiologic changes of pregnancy affect the chemistry and biology of the pituitary, thyroid, and adrenal hormones, which hampers the identification of these endocrine dysfunctions and their treatment. A deep understanding of the biology of pregnancy and endocrinology is needed to diagnose and treat these patients well.

Endocrine disorders may be affected by the gestational state, with its large quantities of pregnancy-secreted hormones, increased overall plasma volume, hypermetabolic state, and altered hormonal feedback mechanisms. This chapter reviews the impact of pregnancy on endocrine diseases with the exception of diabetes, which is discussed separately in a different chapter because it is the most prevalent endocrinopathy. Thyroid disorder is the next most frequent endocrinopathy of reproductive-aged women. Our chapter starts with thyroid disease, followed by parathyroid disease, adrenal disorder, and finally by pituitary disorders.

THYROID PHYSIOLOGY IN PREGNANCY

Pregnancy alters both normal thyroid function and thyroid diseases in 3 main ways: changes in iodine physiology; increases in pregnancy hormone (human chorionic gonadotropin, hCG), which simulates thyroid hormone; and increases in thyroxine-binding globulin (TBG) affect the amount of free hormone.

Brief Review of the Normal Hypothalamic-Pituitary-Thyroid System

The thyroid gland is located in the lower front of the neck, just below the larynx; it comprises two lobes connected by the isthmus. The lobes are divided into lobules containing follicular cells, which produce a glycoprotein material called colloid into the follicular lumen. The thyroid gland extracts iodine from dietary intake to incorporate into the thyroid hormone to produce two hormones: thyroxine (T₄, which has 4 iodine molecules) or triiodothyronine (T₃, which has 3 iodine molecules). These hormones are stored in the thyroid until needed. T₃ is made from T₄ by cleaving 1 iodine molecule.

Regulation of thyroid function occurs through the hypothalamic-pituitary-thyroid axis. Within the paraventricular nucleus of the hypothalamus, thyrotropin-releasing hormone (TRH) is created and is regulated by tonic stimulation in response to positive/negative feedback (Figure 22-1). TRH is secreted via the pituitary portal circulation, where it acts as an agonist on anterior pituitary thyrotrope cells. It modulates the manufacture and ...