Recently, we discussed how postpartum hemorrhage, bleeding that occurs after childbirth as one of the most common obstetric emergencies. Resulting from a variety of causes, including uterine atony (failure of the uterus to contract after delivery), lacerations in the genital tract, and retained placental fragments, postpartum hemorrhage is more likely in the presence of certain risk factors, such as prolonged labor, instrumental delivery, uterine dysfunction, and previous postpartum hemorrhage. Although bleeding can be heavy and accompanied by abdominal pain and abnormal uterine contractions, postpartum hemorrhage usually resolves with appropriate treatment that typically includes administration of fluids and blood products, medications to stimulate uterine contractions, manual removal of placental fragments, and, when needed, surgery. While a common complication of the blood loss is anemia that usually is easily treated, there also are a variety of worse complications, one of them being Sheehan syndrome.
A rare complication, whose incidence has fluctuated among reports from different countries and over the past several decades, Sheehan syndrome is a condition in which postpartum hemorrhage results in poor circulation of blood through the anterior portion of the pituitary gland. This results in various endocrine abnormalities.
We have discussed the endocrine system in a previous post, but to understand Sheehan syndrome we need to dive just a bit into the anatomy of the pituitary and also review how the pituitary functions and hormones that it releases into the blood. The endocrine system consists of the pituitary and the hypothalamus, both located in the brain, plus various glands — the thyroid and parathyroid glands (located in the neck), the adrenal glands (located on top of the kidneys), the pineal body (located in the brain), the ovaries in women, the testes in men, and cells in the pancreas producing insulin and glucagon. Many (not all) of these glands are affected by hormones that the pituitary secretes, but the pituitary is also affected by the hypothalamus and by hormones of the other glands that pituitary hormones affect. In other words, there are loops of hormones. As an example, cells of the hypothalamus secrete thyroid release hormone (TRH), which causes the pituitary to release thyroid stimulating hormone (TSH). TSH, in turn, causes the thyroid gland to release the hormones T3 and T4, which have numerous effects throughout the body. However, as the concentrations of T3 and T4 rise in the blood, they inhibit the pituitary from releasing TSH and the hypothalamus from releasing TRH. Like the thermostat in your home turning off the heat when the temperature rises beyond a certain point, this is a negative feedback loop that keeps the levels of thyroid hormones from rising too high, but also keeps them from getting too low, like your thermostat turning the heat back on when the temperature drops back down.
The pituitary has an anterior section and a posterior section, each of which makes and releases pituitary hormones. The posterior pituitary, for instance, releases oxytocin (the hormone that makes your uterus contract during labor and delivery) and antidiuretic hormone antidiuretic hormone (ADH), which keeps the kidneys from releasing too much water into the urine. These posterior pituitary hormones are not affected in Sheehan syndrome, because the posterior pituitary system has a blood supply that is not so vulnerable to drops in blood pressure and blood volume.
But the anterior pituitary blood supply is different because much of its blood comes from what doctors call the hypophyseal portal system. This system of blood vessels brings blood directly from the hypothalamus. In Sheehan syndrome, a reduction in blood pressure and the circulating blood volume causes reduced perfusion of the anterior pituitary, leading to what doctors call avascular necrosis and ischemia of the anterior pituitary cells, many of which die. These cells in the anterior pituitary are responsible for making several hormones: TSH (which we discussed earlier in our example of feedback loops), adrenocorticotropic hormone (ACTH) follicle stimulating hormone (FSH), luteinizing hormone (LH) growth hormone (GH), and prolactin.
In Sheehan syndrome, the anterior pituitary stops making these hormones, or makes less of them, leading to symptoms of their deficiency. Lack of prolactin means reduced lactation, so you cannot breastfeed. Lack of FSH and LH causes amenorrhea (lack of menstruation, or menstruation does not return after pregnancy. Lack of ACTH leads the adrenal glands to decrease or stop releasing cortisol. This is adrenal insufficiency, leading to adrenal crisis. Lack of TSH causes hypothyroidism, low thyroid hormones.
Women who develop Sheehan syndrome are managed by doctors specializing in endocrinology. Working in concert with your obstetrician and primary care doctor, the endocrinologist oversees replacement of the various missing hormones, resulting from the lack of anterior pituitary hormones. These hormones may include estrogen and progesterone, hydrocortisone, and levothyroxine.
