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Physiologic and Psychosocial Adaptations to Pregnancy
A look at pregnancy changes During pregnancy, a woman undergoes many physiologic and psychosocial changes. Her body adapts in response to the demands of the growing fetus while her mind prepares for the responsibilities that come with becoming a parent. Physiologic changes initially indicate pregnancy; these changes continue to affect the body throughout pregnancy as the fetus grows and develops. Psychosocial changes occur in both the mother and father and may vary from trimester to trimester.
Physiologic signs of pregnancy Pregnancy produces several types of physiologic changes that must be evaluated before a definitive diagnosis of pregnancy is made. The changes can be: Neither presumptive nor probable signs confirm pregnancy because both can be caused by other medical conditions; they simply suggest pregnancy, especially when several are present at the same time. (See Making sense out of pregnancy signs.)
Presumptive signs of pregnancy Presumptive signs of pregnancy are those that can be assumed to indicate pregnancy until more concrete signs develop. These signs include breast changes, nausea and vomiting, amenorrhea, urinary frequency, fatigue, uterine enlargement, quickening, and skin changes. A pregnant patient typically reports some presumptive signs.
Tingling, tender, or swollen breasts can occur as early as a few days after conception. The areola may darken and tiny glands around the nipple, called Montgomery tubercles, may become elevated.
At least 50% of pregnant women experience nausea and vomiting early in pregnancy (commonly called morning sickness). These symptoms are typically the first sensations experienced during pregnancy. Nausea and vomiting usually begins at 4 to 6 weeks’ gestation. These symptoms usually stop at the end of the first trimester, but they may last slightly longer in some patients.
Amenorrhea is the cessation of menses. For a woman who has regular menses, this may be the first indication that she’s pregnant.
A pregnant woman may notice an increase in urinary frequency during the first 3 months of pregnancy. This symptom continues until the uterus rises out of the pelvis and relieves pressure on the bladder.
Urinary frequency may return at the end of pregnancy as lightening occurs (the fetal head exerts renewed pressure on the bladder).
A pregnant woman may report that she’s often fatigued. During the first trimester, the woman’s body works hard to manufacture the placenta and to adjust to the many other physical demands of pregnancy while she mentally and emotionally prepares for motherhood. Around 16 weeks’ gestation, the body has adjusted to the pregnancy, the placenta’s development is complete, and the patient should start to have more energy.
Softening of the uterus and fetal growth cause the uterus to enlarge and stretch the abdominal wall.
Quickening is recognizable movements of the fetus. It can occur anywhere between the 14th and 26th weeks of pregnancy but typically is noticed between weeks 18 and 22.
To the patient, quickening may feel like fluttering movements in her lower abdomen.
Numerous skin changes occur during pregnancy, including those listed here:
Probable signs of pregnancy Probable signs of pregnancy strongly suggest pregnancy. They’re more reliable indicators of pregnancy than presumptive signs, but they can also be explained by other medical conditions. Probable signs include positive laboratory tests, such as serum and urine tests; positive results on a home pregnancy test; Chadwick sign; Goodell sign; Hegar sign; sonographic evidence of a gestational sac; ballottement; and Braxton Hicks contractions.
Laboratory tests for pregnancy are used to detect the presence of human chorionic gonadotropin (hCG)—a hormone created by the chorionic villi of the placenta—in the urine or blood serum of the woman. Because hCG is produced by trophoblast cells— preplacental cells that wouldn’t be present in a nonpregnant woman—detection of hCG is considered a sign of pregnancy. Because laboratory tests for diagnosing pregnancy are accurate only 95% to 98% of the time, positive hCG results are considered probable rather than positive.
Looking for hCG in all the right places Tests for hCG include radioimmunoassay, enzyme-linked immunosorbent assay, and radioreceptor assay. For these tests, hCG is measured in milli-international units (mIU). In pregnant women, trace amounts of hCG appear in the serum as early as 24 to 48 hours after implantation of the fertilized ovum. They reach a measurable level of about 50 mIU/ml between 7 and 9 days after conception. Levels peak at about 100 mIU/ml between the 60th and 80th days of gestation. After this point, the level declines. At term, hCG is barely detectable in serum or urine.
Home pregnancy tests, which are available over-the-counter, are 97% accurate when performed correctly. They’re convenient and easy to use, taking only 3 to 5 minutes to perform.
Here’s how the home pregnancy test works:
Most manufacturers suggest that a woman wait until the day of the missed menstrual period to test for pregnancy.
Chadwick sign is a bluish coloration of the mucous membranes of the cervix, vagina, and vulva. It can be observed at 6 to 8 weeks’ gestation by bimanual examination.
Goodell sign is a softening of the cervix that occurs at 6 to 8 weeks’ gestation. The cervix of a nonpregnant woman typically has the same consistency as the tip of the nose; the cervix of a pregnant woman feels more like an earlobe.
Hegar sign is a softening of the uterine isthmus that can be felt on bimanual examination at 6 to 8 weeks’ gestation. As pregnancy advances, the isthmus becomes part of the lower uterine segment. During labor, it expands further.
Ultrasonography, or sonographic evaluation, can detect probable and positive signs of pregnancy. At 4 to 6 weeks’ gestation, a characteristic ring indicating the gestational sac is visible on sonographic evaluation, making this a probable rather than a positive sign of pregnancy.
Ballottement is passive movement of the fetus. It can be identified at 16 to 18 weeks’ gestation.
Braxton Hicks contractions Braxton Hicks contractions are uterine contractions that begin early in pregnancy and become more frequent after 28 weeks’ gestation. Typically, they result from normal uterine enlargement that occurs to accommodate the growing fetus. Sometimes, however, they may be caused by a uterine tumor.
Positive signs of pregnancy Positive signs of pregnancy include sonographic evidence of the fetal outline, an audible fetal heart rate, and fetal movement that’s felt by the examiner. These signs confirm pregnancy because they can’t be attributed to other conditions.
Ultrasonography can confirm pregnancy by providing an image of the fetal outline, which can typically be seen by the 8th week. The fetal outline on the ultrasound is so clear that a crown to rump measurement can be made to establish gestational age. Fetal heart movement may be visualized as early as 7 weeks’ gestation.
Fetal heart rate can be confirmed by auscultation or visualization during an ultrasound. Fetal heart sounds may be heard as early as the 10th to 12th week by Doppler ultrasonography.
Even though the pregnant woman can feel fetal movement at a much earlier date (usually around 16 to 20 weeks), other people aren’t able to feel fetal movement until the 20th to 24th week. Obese patients may not feel fetal movement until later in pregnancy because of excess adipose tissue.
Physiologic changes in body systems As the fetus grows and hormones shift during pregnancy, physiologic adaptations occur in every body system to accommodate the fetus. These changes help a pregnant woman to maintain health throughout the pregnancy and to physically prepare for childbirth. Physiologic changes also create a safe and nurturing environment for the fetus. Some of these changes take place even before the woman knows that she’s pregnant.
In addition to the physical changes that initially indicate pregnancy, such as Hegar sign and Goodell sign, the reproductive system undergoes significant changes throughout pregnancy.
External reproductive structures affected by pregnancy include the labia majora, labia minora, clitoris, and vaginal introitus. These structures enlarge because of increased vascularity. Fat deposits also contribute to the enlargement of the
Internal reproductive structures, including the ovaries, uterus, and other structures, change dramatically to accommodate the developing fetus. These internal structures may not regain their prepregnant states after childbirth.
When fertilization occurs, ovarian follicles cease to mature and ovulation stops. The chorionic villi, which develop from the fertilized ovum, begin to produce hCG to maintain the ovarian corpus luteum. The corpus luteum produces estrogen and progesterone until the placenta is formed and functioning. At 8 to 10 weeks’ gestation, the placenta assumes production of these hormones. The corpus luteum, which is no longer needed, then involutes (becomes smaller due to a reduction in cell size).
In a nonpregnant woman, the uterus is smaller than the size of a fist, measuring approximately 7.5 cm × 5 cm × 2.5 cm (3″ × 2″ × 1″). It can weigh 60 to 70 g (2 to 2½ oz) in a nulliparous patient (a patient who has never been pregnant) and 100 g (3½ oz) in a parous patient (a patient who has given birth). In a nonpregnant state, a woman’s uterus can hold up to 10 ml of fluid. Its walls are composed of several overlapping layers of muscle fibers that adapt to the developing fetus and help in expulsion of the fetus and placenta during labor and childbirth.
More strength, more stretch After conception, the uterus retains the developing fetus for approximately 280 days or 9 calendar months. During this time, the uterus undergoes progressive changes in size, shape, and position in the abdominal cavity. In the first trimester, the pear-shaped uterus lengthens and enlarges in response to elevated levels of estrogen and progesterone. This hormonal stimulation primarily increases the size of myometrial cells (hypertrophy), although a small increase in cell number (hyperplasia) also occurs. These changes increase the amount of fibrous and elastic tissue to During the first few weeks of pregnancy, the uterine walls remain thick and the fundus rests low in the abdomen. The uterus can’t be palpated through the abdominal wall. After 12 weeks of pregnancy, however, the uterus typically reaches the level of the symphysis pubis (the joint at the pubic bone) and then may be palpated through the abdominal wall.
In the second trimester, the corpus and fundus become globeshaped. As pregnancy progresses, the uterus lengthens and becomes oval in shape. The uterine walls thin as the muscles stretch; the uterus rises out of the pelvis, shifts to the right, and rests against the anterior abdominal wall. At 20 weeks’ gestation, the uterus is palpable just below the umbilicus and reaches the umbilicus at 22 weeks’ gestation. As uterine muscles stretch, Braxton Hicks contractions may occur, helping to move blood more quickly through the intervillous spaces of the placenta.
In the third trimester, the fundus reaches nearly to the xiphoid process (the lower tip of the breast bone). Between weeks 38 and 40, the fetus begins to descend into the pelvis (lightening), which causes fundal height to gradually drop. The uterus remains oval in shape. Its muscular walls become progressively thinner as it enlarges, finally reaching a muscle wall thickness of 5 mm (¼″) or less. At term (40 weeks), the uterus typically weighs approximately 1,100 g (2 lb), holds 5 to 10 L of fluid, and has stretched to approximately 28 cm × 24 cm × 21 cm (11″ × 9½″ × 8½″). (See Fundal height throughout pregnancy, page 118.)
During the menstrual cycle, progesterone stimulates increased thickening and vascularity of the endometrium, preparing the uterine lining for implantation and nourishment of a fertilized ovum. After implantation, menstruation stops. The endometrium then becomes the decidua, which is divided into three layers:
As the fetus grows and the placenta develops, uterine blood vessels and lymphatics increase in number and size. Vessels must enlarge to accommodate the increased blood flow to the uterus and placenta. By the end of pregnancy, an average of 500 ml of blood may flow through the maternal side of the placenta each minute. Maternal arterial pressure, uterine contractions, and maternal position affect uterine blood flow throughout pregnancy. Because one-sixth of the body’s blood supply is circulating through the uterus at any given time, uterine bleeding during pregnancy is always potentially serious and can result in major blood loss. (See Uterine bleeding.)
The cervix consists of connective tissue, elastic fibers, and endocervical folds. This composition allows it to stretch during childbirth. During pregnancy, the cervix softens. It also takes on a bluish color during the second month due to increased vasculature. It becomes edematous and may bleed easily on examination or sexual activity.
During pregnancy, hormonal stimulation causes the glandular cervical tissue to increase in cell number and become hyperactive, secreting thick, tenacious mucus. This mucus thickens into a mucoid weblike structure, eventually forming a mucus plug that blocks the cervical canal. This creates a protective barrier against bacteria and other substances attempting to enter the uterus.
During pregnancy, estrogen stimulates vascularity, tissue growth, and hypertrophy in the vaginal epithelial tissue. White, thick, odorless, and acidic vaginal secretions increase. The acidity of these secretions helps prevent bacterial infections but, unfortunately, also fosters yeast infections, a common occurrence during pregnancy. (See Fighting Candida infection.) Other vaginal changes include:
In addition to the presumptive signs that occur in the breasts during pregnancy (such as tenderness, tingling, darkening of the areola, and appearance of Montgomery tubercles), the nipples enlarge, become more erectile, and darken in color. The areolae widen from a diameter of less than 3 cm (1½″) to 5 or 6 cm (2″ or 3″) in the primigravid patient. Rarely, patches of brownish discoloration appear on the skin adjacent to the areolae. These patches, known as secondary areolae, may indicate pregnancy if the patient has never breast-fed an infant.
The breasts also undergo several changes in preparation for lactation. As blood vessels enlarge, veins beneath the skin of the breasts become more visible and may appear as intertwining patterns over the anterior chest wall. Breasts become fuller and heavier as lactation approaches. This is mammogenesis. The breasts increase in size and weight and there is a proliferation of ductular sprouting, branching and lobular formation, which forms the glandular Increasing hormone levels cause the secretion of colostrum (a yellowish, viscous fluid) from the nipples. High in protein, antibodies, and minerals—but low in fat and sugar relative to mature human milk—colostrum may be secreted as early as week 16 of pregnancy, but it’s most common during the last trimester. It continues secreting until 2 to 4 days after delivery and is followed by lactogenesis stage 2, triggered by the rapid drop in mother’s progesterone levels causing the onset of copious secretion of the milk.
More change for first-timers Breast changes are more pronounced in a primigravida patient than in a multigravida patient. In a multigravida patient, changes are even less significant if the patient has breast-fed an infant within the past year because her areola are still dark and her breasts enlarged. (See Comparing the nonpregnant and pregnant breast.)
The endocrine system undergoes many fluctuations during pregnancy. Changes in hormone levels and protein production help support fetal growth and maintain body functions.
The most striking change in the endocrine system during pregnancy is the addition of the placenta. The placenta is a finite, endocrine organ that produces large amounts of estrogen, progesterone, hCG, hPL, relaxin, and prostaglandins. The estrogen produced by the placenta causes breast and uterine enlargement as well as palmar erythema (redness in the palm of the hand). Progesterone helps maintain the endometrium by inhibiting uterine contractility. It also prepares the breasts for lactation by stimulating breast tissue development.
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When the lower uterine segment is tapped on a bimanual examination the fetus can be felt on rise against the abdominal wall?
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