Occasionally, symptomatic nasopharyngeal obstruction and nasal stuffiness occur, eustachian tubes are transiently blocked, and the tone and quality of voice change. Mild dyspnea during exertion is consistently noted, and deep respirations occur more frequently. As pregnancy progresses, the enlarging uterus pressing against the rectum and lower portion of the colon may cause constipation. In addition, GI motility decreases because elevated progesterone levels relax smooth muscle. Heartburn and belching are common, possibly resulting from delayed gastric emptying and gastroesophageal reflux due to relaxation of the lower esophageal sphincter and diaphragmatic hiatus.
Pregnancy subtly affects hepatic function, especially bile transport.
Pregnancy alters the function of most endocrine glands, partly because the placenta produces hormones and partly because most hormones circulate in protein-bound forms and protein binding increases in pregnancy. The placenta may produce a form of ACTH that increases adrenal gland function. Adrenal hormone levels increase, probably causing the pink skin striae known as stretch marks and contributing to edema. Increased levels of glucocorticoids, estrogens, and progesterone modify glucose metabolism and increase the need for insulin, as does the stress of pregnancy and possibly the increased level of human placental lactogen. Commonly, pigment in the mammary areolae increases, and a dark line appears down the midabdomen.