CHAPTER 5
Physiology of Pregnancy
1 Describe systemic changes occurring in a woman’s body during pregnancy.
2 Describe changes in the uterus, cervix, vagina, and vulva during pregnancy.
3 Identify the presumptive, probable, and positive diagnostic signs and symptoms of pregnancy.
4 Differentiate between normal and abnormal laboratory findings observed during pregnancy.
5 Define optimal nutritional adequacy based on pregnancy outcome indicators.
6 Identify specific changes in nutrient requirements during pregnancy.
7 Examine weight gain recommendations during pregnancy for different women.
8 Design an individualized patient education plan based on data from the history.
9 Detect potential complications of pregnancy based on data from a history, a physical examination, and laboratory test results.
10 Formulate nursing interventions to prevent anticipated problems identified from the nursing assessment.
INTRODUCTION AND BACKGROUND
A Conception and 40 weeks’ gestation involve numerous maternal physiologic adaptations.
1. Regular health care supervision is necessary to ensure that subtle and untoward changes will not go undetected, ensuring a positive outcome for mother, infant, and the entire family. It is necessary for the nurse to be knowledgeable of the physiologic changes of pregnancy to provide competent, high-quality care.
2. The course of pregnancy and the outcome are directly related to the nutritional status of the mother.
3. The health care team is responsible for monitoring expected physiologic and psychologic changes and for providing health teaching for greater understanding of the events of pregnancy as well as preparation for parturition and postpregnancy events.
(1) Size increases to 20 times that of nonpregnant size.
(a) Hyperplasia and hypertrophy of myometrial cells, including muscle fibers, occur.
(b) Increases are related to estrogen and progesterone, with mechanical factors of stretching related to the developing fetus.
(2) Wall thins to 1.5 cm (0.6 inch) or less (changes from almost a solid globe to a hollow vessel).
(3) Weight increases from 70 to 1100 g (1.8 ounces to 2.2 pounds).
(4) Volume (capacity) increases from less than 10 mL to 5 L (2 teaspoons to 1 gallon).
(5) Uterine contractility (Braxton Hicks contractions)
(a) Irregular, painless contractions due to structural and functional changes in myometrium resulting from estrogen increases in pregnancy
(b) As pregnancy advances, these contractions become more intense, frequent, and easily felt.
(c) Braxton Hicks contractions do not typically lead to cervical changes.
(6) Shape changes from that of an inverted pear to that of a soft globe that enlarges, rising out of the pelvis by the end of the first trimester.
(7) Endometrium is called the decidua after implantation.
(1) Softening related to increased vascularity, edema, slight hypertrophy, and hyperplasia (Goodell’s sign)
(2) Cervical glands occupy approximately half of the cervical mass near term.
(3) Mucus plug (operculum) fills the cervical canal soon after conception.
c. Ovaries and fallopian tubes
(1) Anovulation results from the suppression of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) related to high levels of estrogen and progesterone.
(2) Corpus luteum remains active for 6 to 7 weeks into pregnancy, producing progesterone and estrogen to maintain pregnancy; after 6 to 7 weeks’ gestation, the placenta will produce the progesterone to maintain pregnancy.
(1) Increased vascularity results in bluish, violet discoloration (Chadwick’s sign)
(2) Hypertrophy and hyperplasia of epithelium and elastic tissues
(3) Leukorrhea, with an acid pH of 3.5 to 6.0, functions to control the growth of pathogens.
(1) Changes begin soon after conception.
(a) Size increases; weight increases by about 400 g (12 ounces).
(d) Blood vessels become more prominent with a twofold increase in blood flow.
(1) Slight enlargement (hypertrophy) (approximately 12%)
(3) Shift in chest contents: heart is displaced upward, forward and to the left in late pregnancy.
(1) Heart rate increases about 15 to 20 beats/minute (20% increase).
(2) Cardiac output increases by 30% to 50% during first two trimesters and then declines to about 20% near term.
(3) Blood volume increases by approximately 1500 mL or 30% to 50% (might be even greater with multiple births) over prepregnancy level.
(4) Stroke volume increases by as much as 30% over prepregnancy level.
(5) Vasodilation occurs because of progesterone.
(a) Readings, positional variations (Lowdermilk & Perry, 2007; Walsh, 2001)
[i] Supine hypotension results from uterine pressure on inferior vena cava (supine hypotensive syndrome).
[ii] Left lateral recumbent position is optimal for cardiac output and uterine perfusion.
[iii] Brachial artery pressure is highest when woman is sitting.
(b) Systolic and diastolic pressures begin to fall in the first trimester; they decrease until midpregnancy and then slowly rise back to the prepregnancy levels.
(7) Venous pressure does not change despite the increase in blood volume.
(1) Red blood cell (RBC) production escalates.
(a) Total RBC volume increases approximately 33% (450 mL) with iron supplementation.
(b) Blood iron levels in RBC volume increase only approximately 20% to 30% (250 mL).
(2) White blood cell (WBC) count increases 5000 to 12,000/mm3; might normally increase to 20,000/mm3 during parturition without infection.
(a) WBCs in pregnant women are less effective in fighting infection and disease than they are in nonpregnant women.
(b) History and physical examination must confirm diagnosis of infection.
(3) Blood volume expansion is made up of increased volume of plasma and increased numbers of RBCs (plasma volume increases more rapidly than RBC production and causes hemodilution or physiologic anemia of pregnancy).
(a) Primary function is to offset blood loss at delivery.
(b) Supplies the hypertrophied vascular system during pregnancy.
(4) Clotting factors increase.
(a) Plasma fibrin levels increase by approximately 40%.
(b) Fibrinogen levels increase by approximately 50%.
(c) Pregnancy is a hypercoagulable state, placing the woman at risk for thrombosis and alterations in coagulation (e.g., disseminated intravascular coagulation).
(5) Hemoglobin and hematocrit decrease (in relation to plasma volume).
a. Respiratory rate and maximal breathing capacity remain unchanged, whereas vital capacity might increase slightly.
b. Tidal volume increases 30% to 40%; minute ventilatory volume and minute oxygen uptake increase as pregnancy advances, as evidenced by deeper breathing.
c. Carbon dioxide output increases.
d. Increased vascularity of the upper respiratory tract is influenced by increased estrogen levels.
e. Thoracic circumference increases by 5 to 7 cm (2 to 3 inches), and the diaphragm elevates approximately 4 cm (1.5 inches).
f. Basal metabolic rate increases and oxygen requirement increases by 15% to 20% to supply the uterine-placental unit and increased cardiac activity.
g. Acid-base balance: arterial blood is slightly more alkaline.
(a) Hormone effects, particularly the influence of progesterone on smooth muscle
(c) Alterations in the cardiovascular system, including increased cardiac output and increased blood volume
(2) Collection system changes (physiologic hydronephrosis)
(b) Ureters elongate and become tortuous; the upper one third of the ureters might dilate (particularly the right ureter).
(c) Urinary stasis or stagnation occurs and increases the danger of pyelonephritis.
(3) Increased urinary frequency is related to the increasing size of the uterus and its pressure on the bladder.
(4) Bladder is pulled up into the abdominal cavity by the growing uterus, and the bladder tone is decreased.
(1) Changes in kidney function occur to accommodate a heavier workload while maintaining stable electrolyte balance and blood pressure.
(2) Urine output is 25% higher during pregnancy.
(3) Laboratory values (Cunningham et al., 2005; Walsh, 2001)
(a) Glucosuria occurs in 20% of pregnant women (might not be abnormal; warrants further evaluation and monitoring).
(b) Proteinuria is abnormal, except in very concentrated urine or in the first-voided specimen on arising (total urine protein of more than 300 mg in 24 hours is a warning of impaired kidney function and/or pregnancy-induced hypertension).
(1) Gums become hyperemic, swollen, and soft (friable) and have a tendency to bleed (estrogen influence).
(2) Saliva becomes more acidic.
(a) Production remains unchanged.
(b) Some women experience increased saliva production (ptyalism) due to decreased swallowing associated with nausea and vomiting.
(1) Smooth muscle relaxation and decreased peristalsis occur related to progesterone influence; this can lead to:
(a) Decreased motility, resulting in fluids and nutrients remaining in the intestine longer, facilitating greater absorption but also resulting in constipation
(b) Hemorrhoids: associated with constipation, increased venous pressure, and pressure of the gravid uterus
(c) Heartburn (pyrosis), slowed gastric emptying, and esophageal regurgitation (reflux)
(2) Positional changes of organs occur because of uterine enlargement.
c. Liver function undergoes insignificant, minor changes.
a. Distention of the abdomen and a shift in the center of gravity can result in lordosis.
b. Relaxation and increased mobility of joints occur because of the hormones relaxin and progesterone, and lead to a characteristic “waddle gait.”
c. Diastasis recti, a separation of the rectus muscles of the abdominal wall, is associated with the enlarging uterus in some women.
d. Relaxation and increased mobilitiy of pelvic joints facilitate labor.
a. Skin undergoes hyperpigmentation (primarily due to estrogen influence).
(1) Melasma (also called chloasma) is the blotchy, brownish “mask of pregnancy.”
(2) Linea alba can darken and become linea nigra (abdomen).
(3) Nipples, areolae, axillae, vulva, and perineum all darken.
b. Hair: some women may note increased growth.
c. Stretch marks (striae gravidarum) in the breasts, abdomen, thighs, and inguinal area result from the separation within connective tissue related to the action of adrenocorticosteroids (Blackburn, 2008).
d. Blood vessels have increased permeability, causing:
e. Skin disorders and skin problems associated with pregnancy include noninflammatory pruritus and acne vulgaris (especially in the first trimester).
a. Pituitary gland (not essential to maintain pregnancy) (Cunningham et al., 2005)
(1) Anterior lobe: slight increase in size
(a) FSH and LH production is suppressed.
(b) Thyrotropin and adrenocorticotropic (ACTH) hormones might increase slightly.
(c) Human chorionic somatomammotropin (hCS; formerly called human placental lactogen) from the placenta has been suggested to be a growth hormone, responsible for breast development.
(d) Prolactin production is increased and ensures lactation.
(2) Posterior lobe: oxytocin production gradually increases as the fetus matures.
b. Thyroid gland activity and hormone production increase.
(1) Gland enlarges (related to increased vascularity and growth of glandular tissue).
(2) Total triiodothyronine (T3) and thyroxine (T4) increase in early pregnancy and remain high until term.
(3) Increases in thyroid hormone levels occur and function to support maternal metabolic changes along with fetal growth and development (Blackburn, 2008).
c. Parathyroid gland activity increases, and blood levels of parathyroid hormone are elevated to meet the demands for growth of the fetal skeleton.
d. Adrenal glands: little change in function
e. Pancreas: insulin production increased throughout pregnancy to compensate for placental hormone insulin antagonism
(1) Insulin antagonists (hCS, estrogen, progesterone, and adrenal cortisol) decrease tissue sensitivity or the ability to use insulin.
(2) Normal pancreatic beta cells can meet the increased demand for insulin.
(1) Estrogen (also from adrenal cortex and later the placenta) is responsible for:
(a) Enlargement of breasts, uterus, and genitals
(c) Alterations in thyroid function and nutrient metabolism
(d) Changes in sodium and water retention
(g) Stimulation of melanin-stimulating hormones, hyperpigmentation
(2) Progesterone from the corpus luteum (later, the placenta) is responsible for:
(a) Facilitating implantation and maintaining the endometrium
(b) Decreasing uterine contractility
(c) Development of secretory ducts and the lobular-alveolar system of the breasts
(e) Reducing smooth muscle tone in renal and gastrointestinal systems
(f) Increasing sensitivity of respiratory system to carbon dioxide
(3) Relaxin from the corpus luteum (later, the placenta) is thought to be responsible for inhibiting uterine contractility and cervical ripening (Blackburn, 2008).
C Pregnancy signs and symptoms
1. Presumptive evidence of pregnancy
(2) Breast changes: increase in size, tenderness
(3) Vaginal mucosa discoloration (Chadwick’s sign; significant sign only in primiparous women)
(4) Skin pigmentation changes (melasma/chloasma, linea nigra, and linea alba)
2. Probable evidence of pregnancy
(1) Abdominal enlargement and striae
(2) Uterine changes: softening of isthmus (Hegar’s sign); cervical softening (Goodell’s sign)
(3) Braxton Hicks contractions
(5) Endocrine tests positive for human chorionic gonadotropin (hCG) levels
3. Positive evidence of pregnancy
D Nutritional consideration during pregnancy: although attitudes have varied over the years and within cultures about desirable weight gain, much of the scientific body of knowledge allows some general observations.
1. Prepregnancy weight and weight gain
a. Weight before pregnancy and weight gain during pregnancy are directly related to the birthweight of the infant and the incidence of morbidity and mortality.
b. Prepregnancy weight and height along with stores of micronutrients affect health and size of the newborn (Kaiser & Allen, 2002).
c. Body mass index (BMI) is commonly used to evaluate weight for height.
(1) BMI is expressed as weight/height2 in which weight is in kilograms (kg) and height is in meters (m).
(2) BMI classifications are used to categorize nutritional status based on prepregnancy measurements (Cesario, 2003).
d. A weight gain of between 11.5 and 16 kg (25 and 35 pounds) is recommended for healthy pregnant women (Reifsnider & Gill, 2000).
(1) Weight gain should be steady throughout the pregnancy and depends on the stage of pregnancy.
(a) Progressive weight gain during pregnancy is essential to ensure normal fetal growth and development and the deposition of maternal stores.
(b) Recommended weight gain during pregnancy is determined largely by prepregnancy weight for height (Lowdermilk & Perry, 2007).
(2) Approximately 200 to 450 g/week (0.5 to 1 pound) should be adequate during the second and third trimesters.
e. Recommended weight gain for overweight women is between 7 and 11.5 kg (15 and 25 pounds), depending on nutritional status and degree of obesity (Cesario, 2003).
(1) Women must be aware of the adverse effects of maternal malnutrition on infant growth and development.
(2) All pregnant women should gain at least enough weight to equal the weight of the products of conception.
(3) Dietary restriction can result in inadequate intake of essential nutrients and in catabolism of fat stores.
(a) This process augments the production of ketones leading to ketonuria, which has been found to be correlated with preterm labor.
(b) Long-term effects of mild ketonemia during pregnancy are not known (see Chapter 22 for discussion of endocrine disorders).
(4) Ideally, obese women should address weight management issues before conception.
f. If prepregnancy weight is estimated at 10% to 20% below ideal body weight, the mother is considered to have poor nutritional status.
2. Nutritional needs during pregnancy
a. Energy and calorie requirements are increased during pregnancy due to deposition of new tissue, increased metabolic expenditure, and increased energy needed to move the pregnant body.
b. Optimal weight gain from a nutritionally sound diet contributes to a successful pregnancy (Lederman, 2001).
c. Nutrients needed during pregnancy can be obtained with a diet that provides all essential nutrients, fiber, and energy in adequate amounts.
(1) Dietary supplementation is justified when there is concern that adequate nutrition or a well-balanced diet is compromised.
(a) Indicators of nutritional risk include:
[ii] Short interval between pregnancies
[iii] Obesity or low prepregnancy weight
[iv] Use of alcohol, drugs, or tobacco
[vi] Poverty; lack of access to food distribution programs
[vii] Multiple-gestation pregnancy
[viii] Medical conditions (e.g., diabetes, heart disease, errors in metabolism)
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