The cervical glands proliferate during pregnancy, and the endocervical tissue resembles a honeycomb that fills with mucus. The mucus plugs the cervical canal and blocks the ascent of bacteria from the vagina into the uterus during pregnancy (Figure 13-2). One of the earliest signs of labor may be “bloody show,” which consists of the mucous plug plus a small amount of blood. This bleeding occurs from disruption of the cervical capillaries as the mucous plug is dislodged when the cervix begins to thin and dilate.

Vaginal cells contain increasing amounts of glycogen, which causes rapid sloughing and increased vaginal discharge. The pH of the vaginal discharge is acidic because of the increased production of lactic acid that results from the action of Lactobacillus acidophilus on glycogen in the vaginal epithelium (Cunningham et al., 2010). The acidic condition helps to prevent growth of harmful bacteria found in the vagina. However, the glycogen-rich environment favors the growth of Candida albicans, so that persistent yeast infections (candidiasis) are common during pregnancy.

Increased vascularity, edema, and connective tissue changes make the tissues of the vulva and perineum more pliable. Pelvic congestion during pregnancy can lead to heightened sexual interest and increased orgasmic experiences.

During pregnancy the breasts change in size and appearance (Figure 13-3). Estrogen stimulates the growth of mammary ductal tissue, and progesterone promotes the growth of lobes, lobules, and alveoli. The breasts become highly vascular, and a delicate network of veins is often visible. If the increase in breast size is extensive, lineal tears in the connective tissue (striae gravidarum or “stretch marks”) may develop.

Characteristic changes in the nipples and areolae occur during pregnancy. The nipples increase in size and become darker and more erect, and the areolae become larger and more pigmented. Women with very light complexions exhibit less change in pigmentation than those with darker skin tones. Sebaceous glands, called tubercles of Montgomery, become more prominent during pregnancy and secrete a substance that lubricates the nipples. In addition, a thick, yellowish fluid (colostrum) is present beginning at 12 to 16 weeks of pregnancy and can readily be expressed from the breasts by the third trimester (Janke, 2008). Secretion of milk is suppressed during pregnancy by high levels of estrogen and progesterone.

The expanded blood volume of pregnancy causes an increase in cardiac output—the amount of blood ejected from the heart each minute. It is based on stroke volume (the amount of blood pumped from the heart with each contraction) and heart rate (the number of times the heart beats each minute). Cardiac output rises up to 50% with half of the rise occurring in the first 8 weeks of gestation (Beckmann, Ling, Barzansky, et al., 2010). The increase in cardiac output is caused primarily by a gain in stroke volume, but the heart rate also rises about 15 to 20 beats per minute (bpm) (Bond, 2011). Cardiac output is most efficient when the woman is lying in the lateral position and least efficient in the supine position.

Systemic vascular resistance diminishes during pregnancy. This change is likely the result of (1) vasodilation caused by the effects of progesterone and prostaglandins; (2) the addition of the uteroplacental unit, which provides low resistance and a greater area for circulation; (3) fetal, maternal, and placental heat production, which causes vasodilation; (4) decreased vascular sensitivity to angiotensin II; and (5) endothelial prostacyclin and endothelial-derived relaxant factors such as nitric oxide (Blackburn, 2013).

Five major changes in blood flow occur during pregnancy (Koos et al., 2010):

Although iron absorption and iron-binding power are increased during pregnancy, sufficient iron is not always supplied by diet. Iron supplementation is needed to promote hemoglobin synthesis and ensure that erythrocyte production is sufficient to prevent iron deficiency anemia (see Chapter 26). During pregnancy, erythrocyte production increases by 30% if the mother takes iron supplements and by 18% without supplementation (Gordon, 2007).

Leukocytes increase during pregnancy, ranging from 5000 to 12,000 cells/mm³ to as high as 15,000 cells/mm³ (Blackburn, 2013). Leukocytes increase further during labor and the early postpartum period, reaching 25,000 to 30,000 cells/mm³ (Cunningham et al., 2010).

Pregnancy is a hypercoagulable state where the mother’s blood clots more readily. This is because of an increase in factors that favor coagulation and a decrease in factors that inhibit coagulation. Fibrinogen (factor I) increases 50% and factors VII, VIII, IX, and X also rise (Beckmann et al., 2010). Fibrinolytic activity (to break down clots) decreases during pregnancy. Platelets may decrease slightly but remain within normal range (Blackburn, 2013). These changes offer some protection from hemorrhage during childbirth, but also increase the risk of thrombus formation. The risk is a particular concern if the woman must stand or sit for prolonged periods, causing stasis of blood in the veins of the legs. (See Table 13-1 for additional changes in blood components.)

Oxygen consumption increases by approximately 20% in pregnancy. Half the oxygen is used by the uterus, fetus, and placenta. The rest is consumed by the breast tissue, and increased cardiac, renal, and respiratory maternal demands (Beckmann et al., 2010). To compensate for the increased need for oxygen, the woman hyperventilates slightly by breathing more deeply, although her respiratory rate remains unchanged. This hyperventilation promotes the transfer of carbon dioxide from fetal to maternal circulation (Monga, 2009).

Hyperventilation also causes a tidal volume (the volume of gas moved into or out of the respiratory tract with each breath) increase of 30% to 40% causing an increase in the respiratory minute volume (the volume of air inspired or expired in 1 minute) (Beckmann et al., 2010). As a result of the elevated minute volume, the partial pressure of carbon dioxide (PCO₂) is lowered. Renal excretion of bicarbonate from the kidneys compensates for the resulting respiratory alkalosis.

Although the enlarging uterus lifts the diaphragm by approximately 4 cm (1.6 inches) by the third trimester, movement of the diaphragm is slightly increased. The total lung capacity is decreased 5% because of the elevated diaphragm (Callahan & Caughey, 2009). The ribs flare, the substernal angle widens, and the thoracic circumference increases by 5 to 7 cm (2 to 3 inches) (Bond, 2011). These changes result from relaxation of the ligaments around the ribs (Blackburn, 2013). Breathing becomes more thoracic than abdominal, adding to the dyspnea many women experience.

Some women experience ptyalism (excessive salivation) that is unpleasant and embarrassing. The cause of ptyalism appears to be stimulation of the salivary glands by the ingestion of starch (Cunningham et al., 2010). Decreased swallowing during nausea and vomiting may also may play a part (Bond, 2011). Small, frequent meals, gum chewing, and oral lozenges offer limited relief.

Some women believe pregnancy adversely affects tooth mineralization, but the teeth do not lose minerals to the fetus. However, existing periodontal disease may be exacerbated during pregnancy and dental care is important.

Elevated levels of progesterone relax all smooth muscle, decreasing gastrointestinal tone and motility. The effect on gastric emptying time is unclear with some studies showing a decrease and others showing no change during pregnancy (Beckmann et al., 2010; Cunningham et al., 2010).

Emptying time of the intestines is increased allowing more time for nutrient absorption. Calcium, amino acids, iron, glucose, sodium, and chloride are better absorbed during pregnancy, but absorption of some of the B vitamins is reduced (Blackburn, 2013). Decreased motility in the large intestine allows time for more water to be absorbed leading to constipation. Hemorrhoids may be caused or exacerbated by constipation if the expectant mother must strain to have bowel movements.

Progesterone causes functional changes of the liver and gallbladder. The gallbladder becomes hypotonic and emptying time is prolonged, resulting in thicker bile and predisposing to the development of gallstones. Reduced gallbladder tone also leads to a tendency to retain bile salts, which can cause itching (pruritus) (Cunningham, et al., 2010).

During the last trimester the liver is pushed upward and backward by the enlarging uterus. Serum alkaline phosphatase rises to two to four times that of nonpregnant women and levels of serum albumin and total protein fall (Williamson & Mackillop, 2009).

The woman experiences frequency of urination throughout pregnancy. Although uterine expansion within the pelvis is one cause of these urinary changes, frequency begins before the uterus is big enough to exert pressure on the bladder. Hormonal influences, the increased blood volume, and changes in glomerular filtration rate (GFR) may play a significant role in urinary frequency (Blackburn, 2013). Many women experience stress or urge incontinence that begins at any time during pregnancy and continues until after delivery. Nocturia is also common.

The bladder, like all smooth muscle, relaxes in response to increasing levels of progesterone. Bladder mucosa becomes congested with blood, and the bladder walls become hypertrophied as a result of stimulation from estrogen. Decreased drainage of blood from the base of the bladder makes the tissues edematous and susceptible to trauma and infection during childbirth. The base of the bladder is pushed forward and upward near the end of pregnancy by pressure from the uterus.

Striae gravidarum or “stretch marks” appear as slightly depressed pink to purple streaks on the abdomen, breasts, and buttocks. Striae fade to white or silvery lines but do not disappear after childbirth. Laser therapy is sometimes used after childbirth to reduce or eliminate severe striae. Many women believe that striae can be prevented by massage with oil, cocoa butter, or vitamin E, but no topical treatment has been found effective (Rapini, 2009). Lotions and antipruritic creams may be effective in controlling the itching that often occurs.

Because fewer follicles are in the resting phase, hair grows more rapidly and less hair falls out during pregnancy. After childbirth, hair follicles return to normal activity. Many women become concerned about the rate of hair loss that begins 2 to 4 months postpartum. They need reassurance that more follicles have returned to the normal resting phase and that excessive hair loss will not continue. Hair growth returns to normal 6 to 12 months after delivery (Beckmann et al., 2010).

During pregnancy, fetal demands for calcium increase, especially in the third trimester. Absorption of calcium from the intestine is increased from the first trimester, and calcium is stored to meet the later needs of the fetus (Blackburn, 2013). The amount of calcium transferred to the fetus is small in comparison with maternal stores, and there is no loss of maternal bone density to supply fetal needs.

During the third trimester, the abdominal muscles may become so stretched that the rectus abdominis muscles separate (diastasis recti). The extent of the separation varies from slight, which is clinically insignificant, to severe, when a large portion of the uterine wall is covered only by peritoneum, fascia, and skin (see Figure 20-4).

Hyperplasia and increased vascularity cause the thyroid gland to enlarge during pregnancy. Early in the first trimester, a rise in total serum thyroxine (T₄) and thyroxine-binding globulin occurs. The level of serum free (unbound) T₄ rises in early pregnancy and then returns to normal. Maternal thyroid hormones are important in the development of the fetal brain. The basal metabolic rate (BMR) increases up to 25% primarily because of the fetal metabolic activity (Cunningham et al., 2010).

Parathyroid hormone, important for calcium homeostasis, decreases during the first trimester but then increases steadily throughout pregnancy (Cunningham et al., 2010). Calcium for transfer to the fetus is adequate.

During pregnancy, alterations in maternal blood glucose and fluctuations in insulin production occur. Glucose levels are 10% to 20% lower than before pregnancy, and hypoglycemia may develop between meals and at night as the fetus draws glucose from the mother (Blackburn, 2013).

During the second half of pregnancy, maternal tissue sensitivity to insulin begins to decline because of the effects of human chorionic somatomammotropin, prolactin, progesterone, estrogen, and cortisol. The mother uses fat stores to meet her energy needs. The higher blood glucose level makes more glucose available for fetal energy needs and stimulates the pancreas of a healthy woman to produce additional insulin. Inadequate insulin production results in gestational diabetes (see Chapter 26).