Physiologic Adaptations During Pregnancy PDF

1/16/24, 10:11 PM Realizeit for Student Physiologic adaptions during pregnancy Every system of a woman's body changes during pregnancy to accommodate the needs of the growing fetus, and these changes occur with startling speed. The physical changes of pregnancy can be uncomfortable, although every...

1/16/24, 10:11 PM Realizeit for Student Physiologic adaptions during pregnancy Every system of a woman's body changes during pregnancy to accommodate the needs of the growing fetus, and these changes occur with startling speed. The physical changes of pregnancy can be uncomfortable, although every woman reacts uniquely. Reproductive System Adaptations Significant changes occur throughout the woman's body during pregnancy to accommodate the growing human being within her. Many have a protective role for maternal homeostasis and are essential in meeting the demands of both the mother and the fetus. Many adaptations are reversible after the woman gives birth, but some persist for life. Uterine growth occurs as a result of both hyperplasia and hypertrophy of the myometrial cells, which do not increase much in number but do increase in size. In early pregnancy, uterine growth is due to hyperplasia of uterine smooth muscle cells within the myometrium; however, the major component of myometrial growth occurs after mid-gestation due to smooth muscle cell hypertrophy caused by mechanical stretch of uterine tissue by the growing fetus (Cunningham et al., 2018). Blood vessels elongate, enlarge, dilate, and sprout new branches to support and nourish the growing muscle tissue, and the increase in uterine weight is accompanied by a large increase in uterine blood flow, which is necessary to perfuse the uterine muscle and accommodate the growing fetus. As pregnancy progresses, 80% to 90% of uterine blood flow goes to the placenta with the remainder distributed between the endometrium and myometrium. During pregnancy, the diameter of the main uterine artery approximately doubles in size. This enlargement from a narrow to a larger-caliber vessel enhances the capacity of the uteroplacental vessels to accommodate the increased blood volume needed to supply the placenta (Kail & Cavanaugh, 2018). Uterine contractility is enhanced as well. Spontaneous, irregular, and painless contractions called Braxton Hicks contractions begin during the first trimester. These contractions continue throughout pregnancy, becoming especially noticeable during the last month, when they function to thin out or efface the cervix before birth. The lower portion of the uterus (the isthmus) does not undergo hypertrophy and becomes increasingly thinner as pregnancy progresses, thereby forming the lower uterine segment. Changes in the lower uterus occurring during the first 6 to 8 weeks’ gestation produce some of the typical findings, including a positive Hegar sign. This softening and compressibility of the lower uterine segment results in exaggerated uterine anteflexion during the early months of pregnancy, which adds to urinary frequency by placing pressure on the bladder (Jordan et al., 2019). The uterus remains in the pelvic cavity for the first 3 months of pregnancy, after which it progressively ascends into the abdomen (Fig. 11.1). As the uterus grows, it presses on the urinary bladder and causes the increased frequency of urination experienced during early pregnancy. In addition, the heavy gravid uterus in the last trimester can fall back against the inferior vena cava in the supine position, resulting in vena cava compression, which reduces venous return and decreases cardiac output and blood pressure, increasing orthostatic stress. This occurs when the woman changes her position from recumbent to sitting to standing. This acute hemodynamic change, termed supine hypotensive syndrome, causes the woman to experience symptoms of weakness, light-headedness, nausea, dizziness, or syncope (Fig. 11.2). These changes are reversed when the woman is in the side-lying position, which displaces the uterus to the left and off the vena cava. FIGURE 11.1 The growing uterus in the abdomen. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 1/3 1/16/24, 10:11 PM Realizeit for Student FIGURE 11.2 Supine hypotensive syndrome. The uterus becomes ovoid as length increases over width. By 20 weeks’ gestation, the fundus, or top of the uterus, is at the level of the umbilicus and measures 20 cm. A monthly measurement of the height of the top of the uterus in centimeters, which corresponds to the number of gestational weeks, is commonly used to date the pregnancy. Take Note! Fundal height can usually be correlated with gestational weeks most accurately between 18 and 32 weeks. Obesity, hydramnios, and uterine fib of this correlation. The fundus reaches its highest level, at the xiphoid process, at approximately 36 weeks. Between 38 and 40 weeks, fundal height drops as the fetus begins to descend and engage into the pelvis. Because it pushes against the diaphragm, many women experience shortness of breath. By 40 weeks, the fetal head begins to descend and engage in the pelvis, which is termed lightening. For the woman who is pregnant for the first time, lightening usually occurs approximately 2 weeks before the onset of labor; for the woman who is experiencing her second or subsequent pregnancy, it usually occurs at the onset of labor. Although breathing becomes easier because of this descent, the pressure on the urinary bladder now increases and the woman now experiences urinary frequency again, as she did in the first trimester of pregnancy. Cervix Between weeks 6 and 8 of pregnancy, the cervix begins to soften (Goodell sign) due to vasocongestion and the influence of estrogen. Along with the softening, the endocervical glands increase in size and number and produce more cervical mucus. Under the influence of progesterone, a thick mucus plug is formed that blocks the cervical os and protects the opening from bacterial invasion. At about the same time, increased vascularization of the cervix causes Chadwick sign, a cyanosis or bluish purple discoloration. Cervical ripening (softening, effacement, and increased distensibility) begins about 4 weeks before birth. The connective tissues of the cervix undergo biochemical modifications in preparation for labor that result in changes to its elasticity and strength. These changes are mediated through several factors, including inflammation, cervical stretch, pressure of the fetal presenting part, and release of hormones, including oxytocin, relaxin, nitric oxide, and prostaglandins (Norwitz et al., 2019). Vagina During pregnancy, vascularity increases because of the influences of estrogen, resulting in pelvic congestion and hypertrophy of the vagina in preparation for the distention needed for birth. The vaginal mucosa thickens, the connective tissue begins to loosen, the smooth muscle begins to hypertrophy, and the vaginal vault begins to lengthen (Leung & Qiao, 2019). Vaginal secretions become more acidic, white, and thick. Most women experience an increase in a whitish vaginal discharge, called leukorrhea, during pregnancy. This is normal except when it is accompanied by itching and irritation, possibly suggesting Candida albicans, a monilial vaginitis, which is a common occurrence in this glycogen-rich environment (Norwitz et al., 2019). Symptomatic vulvovaginal candidiasis affects 15% of pregnant women (King et al., 2019). It is a benign fungal condition that is uncomfortable for the woman and can be transmitted from an infected mother to her newborn at birth. Neonates develop an oral infection known as thrush, which presents as white patches on the mucous membranes of their mouths. It is self-limiting and is treated with local antifungal agents. Ovaries The increased blood supply to the ovaries causes them to enlarge until approximately the 12th to 14th week of gestation. The ovaries are not palpable after that time because the uterus fills the pelvic cavity. Ovulation ceases during pregnancy because of the elevated levels of estrogen and progesterone, which block secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. The ovaries are active in hormone production to support the pregnancy until about weeks 6 to 7, when the corpus luteum regresses and the placenta takes over the major production of progesterone. Breasts https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 2/3 1/16/24, 10:11 PM Realizeit for Student The breasts increase in fullness, become tender, and grow larger throughout pregnancy under the influence of estrogen and progesterone. The breasts become highly vascular, and veins become visible under the skin. The nipples become larger and more erect. Both the nipples and the areola become deeply pigmented, and tubercles of Montgomery (sebaceous glands) become prominent. These sebaceous glands keep the nipples lubricated for breastfeeding. Changes that occur in the connective tissue of the breasts, along with the tremendous growth, lead to striae (stretch marks) in approximately half of all pregnant women (Jordan et al., 2019). Initially they appear as pink to purple lines on the skin, but they eventually fade to a silver color. Although they become less conspicuous in time, they never completely disappear. Creamy, yellowish breast fluid called colostrum can be expressed from the breast, if squeezed, by the third trimester. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 3/3