Chapter 6 - Maternal Adaptations to pregnancy

Mucus plug

A less obvious change occurs as the cervical glands proliferate during pregnancy, and the glandular walls become thin and widely separated. As a result, the endocervical tissue resembles a honeycomb that fills with mucus secreted by the cervical glands. The mucus, which is rich in immunoglobulins, forms a plug in the cervical canal. It blocks the ascent of bacteria from the vagina into the uterus during pregnancy to help protect the fetus and the uterine membranes from infection The mucous plug remains in place until term, when the cervix begins to thin and dilate, allowing the mucous plug to be expelled. One of the earliest signs of labor may be "bloody show," which consists of the mucous plug and a small amount of blood. Bleeding is produced by disruption of the cervical capillaries as the mucous plug is dislodged when the cervix begins to thin and dilate.

Blood Components

Although iron absorption is increased during pregnancy, sufficient iron is not always supplied by the diet. Iron supplementation is necessary to promote hemoglobin synthesis and ensure erythrocyte production adequate to prevent iron deficiency anemia. Leukocytes increase during pregnancy, ranging from 5000 cells/mm3 to 12,000 cells/mm3 or as high as 15,000 cells/mm3. Leukocytes increase further during labor and the early postpartum period, reaching levels of 25,000 cells/mm3 to 30,000 cells/mm3. Pregnancy is a hypercoagulable state because of an increase in factors that favor clotting and a decrease in factors that inhibit clotting. Fibrinogen (factor I), fibrin split products, and factors VII, VIII, IX, and X rise by 50%. These changes increase the ability to form clots. Fibrinolytic activity (to break down clots) decreases during pregnancy. The platelet count may decrease slightly but generally remains within the normal range. These changes offer some protection from hemorrhage during childbirth but also increase the risk for thrombus formation. The risk is a concern if the woman must stand or sit for prolonged periods with stasis of blood in the veins of the legs.

Gastrointestinal System Liver and Gallbladder

Although the size of the liver and gallbladder remains unchanged during pregnancy, estrogen and progesterone cause functional changes. The enlarging uterus pushes the liver upward and backward during the last trimester, and liver function is also altered. The serum alkaline phosphatase level rises two to four times that in nonpregnant women. Serum albumin and total protein fall, partly because of hemodilution The gallbladder becomes hypotonic, and emptying time is prolonged. The bile becomes thicker, predisposing to the development of gallstones. Reduced gallbladder tone also leads to a tendency to retain bile salts, which can cause itching (pruritus)

Effect of position and other variables

An accurate BP is affected by the maternal position. Systolic pressure remains largely unchanged or decreases slightly if it is measured when the woman is sitting or standing. Arterial pressures are approx 10 mm Hg lower when the pregnant woman is in a side-lying or supine position than when she is sitting or standing. The most accurate and therefore preferred measurement is obtained with the woman is in a sitting position. The arm should be at the level of the heart. If the arm is above the heart, the reading will be lower; if the arm is below the heart, the reading will be higher. The size of the cuff can affect the reading. A small cuff will show a higher reading and a large cuff will show a lower reading. It is important at every prenatal visit to measure the blood pressure with the woman in a seated position and using the appropriate cuff size. In addition, the same arm and position should be used consistently. These variables should be documented with the blood pressure reading. Blood pressure can also be affected by age, activity, anxiety, chronic health conditions, pain, smoking, or use of alcohol or medication.

Respiratory Changes

Are the result of three factors Increased oxygen consumption Hormonal factors and the physical effects of the enlarging uterus

Blood Pressure

Blood pressure is an indirect measurement of the systemic vascular resistance. Due to the increased blood volume, the blood pressure changes during pregnancy are minimal. The diastolic pressure decreases slightly (about 10 to15 mm Hg) due to the influence of progesterone. This begins at six weeks of pregnancy and is most noticeable by the beginning of the third trimester

Heart size and position

Changes in the size and position of the heart are minor and reverse soon after childbirth. The muscles of the heart (myocardium) enlarge 10% to 15% during the first trimester. The heart is pushed upward and to the left as the uterus elevates the diaphragm during the third trimester. As a result of the change in position, the locations for auscultation of heart sounds may be shifted upward and laterally in late pregnancy.

Cutaneous vascular changes

During pregnancy, blood vessels dilate and proliferate, which is an effect of estrogen. Changes in surface blood vessels are obvious during pregnancy, especially in women with fair skin. These include angiomas (vascular spiders, telangiectasia) that appear as tiny red elevations branching in all directions and occur most often on areas exposed to the sun. Redness of the palms of the hands or soles of the feet, known as palmar erythema, also occurs in many White women and some African American women. Vascular changes may be emotionally distressing for the expectant mother, but they are clinically insignificant and usually disappear shortly after childbirth.

Physical Effects of the enlarging uterus

During pregnancy, the enlarging uterus lifts the diaphragm approximately 4 cm (1.6 inches). The elevation of the diaphragm does not impede its movement which is increased by about 1 to 2 cm (0.4 to 0.8 inch) during respirations. The ribs flare, the substernal angle widens, and the transverse diameter of the chest expands by about 2 cm (0.8 inches) to compensate for the reduced space. These changes begin when the uterus is just beginning to enlarge. They result from the hormone relaxin, which causes relaxation of the ligaments around the ribs. Breathing becomes thoracic rather than abdominal, adding to the dyspnea that as many as 60% to 70% of women experience beginning in the first or second trimester

Gastrointestinal System Mouth

Elevated levels of estrogen cause hyperemia of the tissues of the mouth and gums and may lead to gingivitis and bleeding gums. Some women develop a highly vascular hypertrophy of the gums, called epulis. The condition regresses spontaneously after childbirth. Although the amount of saliva does not usually change, some women experience ptyalism, or excessive salivation. The cause of ptyalism may be decreased swallowing, associated with nausea or stimulation of the salivary glands by the ingestion of starch. Small, frequent meals and use of chewing gum and oral lozenges offer limited relief to some women. Many women think that pregnancy causes loss of mineral from teeth to meet fetal needs. However, this is not true, and the tooth enamel is stable during pregnancy. Tooth decay may occur because of changes in salvia and the nausea and vomiting of pregnancy. Periodontal disease may result in infections that precipitate labor.

Gastrointestinal System Large and small intestines

Emptying time of the intestines increases, allowing more time for nutrient absorption. It also may cause bloating and abdominal distention. Calcium, iron, some amino acids, glucose, sodium, and chloride are better absorbed during pregnancy, but absorption of some of the B vitamins is reduced. Decreased motility in the large intestine allows time for more water to be absorbed, leading to constipation. Constipation may cause or exacerbate hemorrhoids if the expectant mother must strain to have bowel movements. Flatulence also may be a problem

Hormonal Factors Estogen

Estrogen causes increased vascularity of the mucous membranes of the upper respiratory tract. As the capillaries become engorged, edema and hyperemia develop within the nose, pharynx, larynx, and trachea. This congestion may cause nasal and sinus stuffiness, epistaxis (nosebleed), and deepening of the voice. Increased vascularity also causes edema of the eardrum and eustachian tubes and may result in a sense of fullness in the ears.

Breasts

Estrogen stimulates the growth of mammary ductal tissue, and progesterone promotes the growth of the lobes, lobules, and alveoli. The breasts become highly vascular, with a delicate network of veins often visible just beneath the surface of the skin. If the increase in breast size is extensive, striation ("stretch marks) similar to those that occur on the abdomen may develop. Characteristic changes in the nipples and the areola become larger and more pigmented. The degree of pigmentation varies with the complexion of the expectant mother. Women with very light skin tones exhibit less change in pigmentation that those with darker skin. 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 secreted as early as 16 weeks of gestation. Secretion of milk is suppressed during pregnancy by the high levels of estrogen and progesterone.

Systemic Vascular Resistace

Falls during pregnancy. This change is likely because of (1) vasodilation resulting from the effects of progesterone and prostaglandins (2) The addition of the uteroplacental unit, which provides a greater area for circulation and low resistance (3) Increased heat production from fetal, placental, and matneral metabolism, which produces vasodilation (4) Decreased sensitivity to angiotensin 2 (5) Endothelial prostacyclin and endothelialderived relaxant factors such as nitric oxide

Blood Flow

Five major changes in blood flow occur during pregnancy • Blood flow is altered to include the uteroplacental unit. • Renal plasma flow increases up to 30% to remove the increased metabolic wastes generated by the mother and the fetus. • The woman's skin requires increased circulation to dissipate heat generated by increased metabolism during pregnancy. • Blood flow to the breasts increases, resulting in engorgement and dilated veins. • The weight of the expanding uterus on the inferior vena cava and iliac veins partially obstructs blood return from veins in the legs. Blood pools in the deep and superficial veins of the legs causing venous distention. Prolonged engorgement of the veins of the lower legs may lead to varicose veins of the legs, vulva, or rectum (hemorrhoids).

Uterus

Growth occurs as the result of hyperplasia and hypertrophy caused by estrogen and other growth factors. Growth can be predicted for each trimester (one of three 13 weeks of pregnancy) In the latter half of pregnancy, uterine growth results mainly from hypertrophy as the muscle fibers stretch in all directions to accommodate the growing fetus. In addition to muscle growth, fibrous tissue accumulates in the outer muscle layer of the uterus and the amount of elastic tissue increases. These changes greatly increase the strength of the muscle wall Muscle fibers in the myometrium increase in both length and width. Although the uterine wall thickens during early pregnancy, the wall of the uterus thins to approximately 0.5 to 1 cm (0.2 to 0.4 inch) and the fetus can be palpated easily through the abdominal wall by term. As the uterus expands into the abdominal cavity, it displaces the intestines upward and laterally. The uterus gradually rotates to the right as a result of pressure from the rectosigmoid colon on the left side of the pelvis.

Skin Hyperpigmentation

Increased pigmentation from elevated levels of estrogen, progesterone, and melanocyte-stimulating hormone occurs in 91% of pregnant women. Women with dark hair or skin exhibit more hyperpigmentation than women with very light coloring. Areas of pigmentation include brownish patches called melasma, chloasma, or the "mask of pregnancy." Melasma involves the forehead, cheeks, and bridge of the nose and occurs in approximately 70% of pregnant women. It also may occur in nonpregnant women taking oral contraceptives. Melasma increases with exposure to sunlight, but use of sunscreen may reduce the severity. Although melasma usually resolves after delivery when estrogen and progesterone levels decline, it continues for months or years in about 30% of women

Vagina and Vulva Changes

Increased vascularity causes the vaginal walls to appear bluish purple. Softening of the abundant connective tissue allows the vagina to distend during childbirth. The vaginal mucosa thickens, and vaginal rugae (folds) become very prominent. Vaginal cells contain increasing amounts of glycogen, which causes rapid sloughing and increased thick, white vaginal discharge. The pH of the vaginal discharge is acidic (3.5 to 6) because of the increased production of lactic acid that results from the action of Lactobacillus acidophilus on glycogen in the vaginal epithelium. The acidic condition helps prevent growth of harmful bacteria in the vagina. However, the glycogen-rich environment favors the growth of Candida albicans, and 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.

Braxton Hicks Contractions

Irregular contractions that the uterus undergoes throughout pregnancies. During the contractions, the uterus temporarily tightens and then returns to its original relaxed state. During the first two trimesters, the contractions are infrequent and usually not felt by the woman. Contractions occur more frequently during the third trimester and may cause some discomfort. They are called false labor when they are mistaken for the onset of early labor, and fail to result in cervical change.

Connective Tissue Striae Gravidarum

Linear tears may occur in the connective tissue, most often on the abdomen, breasts, and buttocks, appearing as slightly depressed, pink to purple streaks called striae gravidarum, or "stretch marks" Women are concerned about striae because they do not disappear after childbirth, although the marks usually fade to silvery lines. Laser therapy is sometimes used after childbirth to reduce or eliminate severe striae. Many women believe that striae can be prevented by massaging with oil, vitamin E, or cocoa butter, but these substances have not been found effective. Antipruritic creams may be effective in controlling the itching that often occur

Ovaries

Progesterone called the "hormone of pregnacy" must be present in adequate amounts from the earliest stages to maintain pregnancy. Progesterone helps suppress contractions of the uterus and also may help prevent tissue rejection of the fetus. After conception, the corpus luteum of the ovaries secretes progesterone, mainly during the first 6 to 7 weeks of pregnancy. Between 6 to 7 weeks of gestation, the corpus luteum produces a smaller amount of progesterone as the placenta takes over production. The corpus luteum the regresses because it is no longer needed. Ovulation ceases during pregnancy because of the high circulating levels of estrogen and progesterone inhibit the release of the follicle stimulating hormone and lutenizing hormone, which are necessary for ovulation.

Hormonal Factors Progesterone

Progesterone is considered a major factor in the respiratory changes of pregnancy. Progesterone, along with prostaglandins, helps decrease airway resistance by up to 50% by relaxing the smooth muscle in the respiratory tract. Progesterone is also believed to increase the sensitivity of the respiratory center in the medulla oblongata to carbon dioxide, thus stimulating the increase in minute ventilation. These two factors are responsible for the heightened awareness of the need to breathe, shortness of breath, and increased respirations experienced by many women during pregnancy

Red Blood Cell Volume

RBC volume increases by approximately 20% to 30% above prepregnancy values. Although both RBC volume and plasma volume expand, the increase in plasma volume is more pronounced and occurs earlier. The resulting dilution of RBC mass causes a decline in maternal hemoglobin and hematocrit. This condition is frequently called physiologic anemia of pregnancy, or pseudoanemia of pregnancy, because it reflects dilution of RBCs in the expanded plasma volume, rather than an actual decline in the number of RBCs, and does not indicate true anemia. Physiologic anemia should not be dismissed as unimportant, however. Frequent laboratory examinations may be needed to distinguish between physiologic and true anemia. Generally, iron deficiency anemia occurs when the hemoglobin is less than 11 grams per deciliter (g/dL) in the first and third trimesters or less than 10.5 g/dL in the second trimester. Iron supplementation is often prescribed for all pregnant women by the second trimester to prevent anemia. Dilution of RBCs by plasma may have a protective function. By decreasing blood viscosity, dilution may counter the tendency to form clots (thrombi) that could obstruct blood vessels and cause serious complications. Hemodilution may also increase placental perfusion

Heart Sounds

Some heart sounds may be so altered during pregnancy that they would be considered abnormal in the nonpregnant state. The changes are first heard between 12 and 20 weeks and continue for 2 to 4 weeks after childbirth. The most common variations in heart sounds include splitting of the first heart sound and a systolic murmur that is found in more than 95% of pregnant women The murmur is best heard at the left sternal border. Up to 90% of pregnant women have a third heart sound

Cardiac Output

The expanded blood volume of pregnancy results in 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 increases 30% to 50% with half of the rise occuring in the first 8 weeks of pregnancy and remains elevated throughout pregnancy. The increase in cardiac output is the result of a gain in stroke volume and a heart rate acceleration that peaks at 15 to 20 beats per minute (bpm) by 32 weeks gestation. Cardiac output is highest when the woman is lying on her side and it is lower in the standing and supine positions.

Pattern of uterine growth

The growth helps confirm the estimated date of delivery. By 12 weeks of gestation, the fundus can be palpated above the symphysis pubis. At 16 weeks the fundus reaches midway between the symphysis pubis and the umbilicus. It is located at the umbilicus at 20 weeks. The fundus reaches its highest level at the xiphoid process at 36 weeks of gestation. It pushes againnst the diaphram, and the expectant mother may experience shortness of breath, even during rest. By 40 weeks, the fetal head descends into the pelvic cavity and the uterus sinks to a lower level. This descent of the fetal head is called lighting because it reduces pressure of the disphram and makes breathing easier. Lightening is more pronounced in first pregnancies.

Skin Linea Nigra

The linea alba -- the line that marks the longitudinal division of the midline of the abdomen - darkens to become the linea nigra. This dark line of pigmentation may extend from the symphysis pubis to as high as the top of the fondus. Preexisiting moles (nevi), freckles, and the areolae become darker as pregnancy progresses. Hyperpigmentation usually disappears after childbirth.

Gastrointestinal System Esophagus

The lower esophageal sphincter tone decreases during pregnancy, primarly because of the relaxant activity of progesterone on the smooth muscles. These changes, along with upward displacement of the stomach, allow gastroesophageal reflux of acidic stomach contents into the esophagus and produces heartburn (pyrosis)

Blood Volume

Total blood volume increases significantly because of a combination of plasma and components such as red blood cells (RBCs, erythrocytes), white blood cells (WBCs, leukocytes), and platelets (thrombocytes). Total blood volume increase begins by 6 weeks of gestation and reaches an average of 30% to 45% during pregnancy. The increased volume is needed to (1) transport nutrients and oxygen to the placenta, where they become available for the growing fetus; (2) meet the demands of the expanded maternal tissue in the uterus and breasts; and (3) provide a reserve to protect the pregnant woman from the adverse effects of blood loss that occurs during childbirth.

Gastrointestinal System Appetite

Unless the woman is nauseated, her appetite is often increased during pregnancy. This helps her consume the additional calories recommended. Food intake may increase by 15% to 20% beginning in early pregnancy

Cervix

Water content and vascularity of the area increase. The most obvious changes occur in color and consistency. Increasing levels of estrogen cause hyperemia (congestion with blood) of the cervix, resulting in the characteristic bluish-purple that extends to include vagina and labia. This discoloration, referred to as the Chadwicks sign, is one of the earliest signs of pregnancy. The cervix is largely composed of connective tissue that softens when the collagen fibers decrease in concentration. Before pregnancy, the cervix has a consistency similar to that of the tip of the nose. After conception the cervix feels more like the lips or earlobe. The cervical softening is referred to as the Goodell's sign.

Supine hypotension

When the pregnant woman is in the supine position, particularly in late pregnancy, the weight of the gravid (pregnant) uterus partially occludes the vena cava and the aorta. The occlusion diminishes return of blood from the lower extremities and consequently reduces cardiac return. Cardiac output may be reduced 25% to 30% when the woman is in this position. As many as 5% to 10% of women develop a drop in BP known as supine hypotensive syndrome, with symptoms of lightheadedness, dizziness, nausea, or syncope (a brief lapse in consciousness) when in the supine position. Blood flow through the placenta also decreases if the woman remains in the supine position for a prolonged time, which could result in fetal hypoxia. Turning the woman to a lateral recumbent position alleviates the pressure on the blood vessels and quickly corrects supine hypotension. Women should be advised to rest in the side-lying position to prevent or correct the occurrence of supine hypotension. If they must lie in the supine position for any reason, a wedge or pillow under one hip may be effective in decreasing supine hypotension.