Changes in Size, Shape, and Position.

High levels of estrogen and progesterone stimulate phenomenal uterine growth in the first trimester. Early uterine enlargement results from increased vascularity and dilation of blood vessels, hyperplasia (production of new muscle fibers and fibroelastic tissue) and hypertrophy (enlargement of preexisting muscle fibers and fibroelastic tissue), and development of the decidua. By 7 weeks of gestation, the uterus is the size of a large hen’s egg; by 10 weeks, it is the size of an orange (twice its nonpregnant size); and by 12 weeks, it is the size of a grapefruit. After the third month, uterine enlargement is primarily the result of mechanical pressure of the growing fetus.

As the uterus enlarges, it also changes in shape and position. At conception, the uterus is shaped like an upside-down pear. During the second trimester, as the muscular walls strengthen and become more elastic, the uterus becomes spherical or globular. Later, as the fetus lengthens, the uterus becomes larger and more ovoid and rises out of the pelvis into the abdominal cavity.

The pregnancy may “show” after the fourteenth week, although this depends to some degree on the woman’s height and weight. Abdominal enlargement may be less apparent in the nullipara with good abdominal muscle tone (Fig. 7-2). Posture also influences the type and degree of abdominal enlargement that occurs. In normal pregnancies, the uterus enlarges at a predictable rate.

As the uterus grows, it may be palpated above the symphysis pubis sometime between the twelfth and fourteenth weeks of pregnancy (Fig. 7-3). The uterus rises gradually to the level of the umbilicus at 22 to 24 weeks of gestation and nearly reaches the xiphoid process at term. Between weeks 38 and 40, fundal height decreases as the fetus begins to descend and engage in the pelvis (lightening) (see Fig. 7-3, dashed line). Generally, lightening occurs in the nullipara about 2 weeks before the onset of labor and in the multipara at the start of labor.

Uterine enlargement is determined by measuring fundal height (see Fig. 8-7). This measurement is commonly used to estimate the duration of pregnancy. However, variation in the position of the fundus or the fetus, variations in the amount of amniotic fluid present, the presence of more than one fetus, maternal obesity, and variation in examiner technique can reduce the accuracy of this estimation.

Generally the uterus rotates to the right as it elevates, probably because of the presence of the rectosigmoid colon on the left side. However, the extensive hypertrophy (enlargement) of the round ligaments keeps the uterus in the midline. Eventually the growing uterus touches the anterior abdominal wall and displaces the intestines to either side of the abdomen (Fig. 7-4). When a pregnant woman is standing, most of her uterus rests against the anterior abdominal wall and contributes to altering her center of gravity.

At approximately 6 weeks of gestation, softening and compressibility of the lower uterine segment (uterine isthmus) occurs (Hegar sign) (Fig. 7-5). This results in exaggerated uterine anteflexion during the first 3 months of pregnancy. In this position, the uterine fundus presses on the urinary bladder, causing the woman to have urinary frequency.

Changes in Contractility.

Soon after the fourth month of pregnancy, uterine contractions can be felt through the abdominal wall. These contractions are referred to as Braxton Hicks contractions. Braxton Hicks contractions are irregular and painless contractions that occur intermittently throughout pregnancy. Although Braxton Hicks contractions are not painful, some women complain that they are annoying. After the twenty-eighth week, these contractions become more definite but they usually cease with walking or exercise. Braxton Hicks contractions can be mistaken for true labor; however, they do not increase in intensity or duration or cause cervical dilation. Conversely, premature labor contractions can be mistaken for Braxton Hicks contractions and lead to a delay in seeking treatment.

Uteroplacental Blood Flow.

Placental perfusion depends on the maternal blood flow to the uterus. Blood flow increases rapidly as the uterus increases in size. Although uterine blood flow increases twentyfold, the fetoplacental unit grows even more rapidly. Consequently, more oxygen is extracted from the uterine blood during the latter part of pregnancy (Cunningham, Leveno, Bloom, et al., 2010). In a normal term pregnancy, one sixth of the total maternal blood volume is within the uterine vascular system. The rate of blood flow through the uterus averages 450 to 650 mL/min at term, and oxygen consumption of the gravid uterus increases to meet fetal needs. Three factors known to decrease uterine blood flow are low maternal arterial pressure, contractions of the uterus, and maternal supine position. Estrogen stimulation may increase uterine blood flow. Doppler ultrasound examination can be used to measure uterine blood flow velocity, especially in pregnancies at risk because of conditions associated with decreased placental perfusion (e.g., hypertension, intrauterine growth restriction, diabetes mellitus, multiple gestation) (Blackburn, 2013).

Using an ultrasound device or a fetal stethoscope, the examiner may hear the uterine souffle or bruit, a rushing or blowing sound of maternal blood flowing through uterine arteries to the placenta that is synchronous with the maternal pulse. The funic souffle, which is synchronous with the fetal heart rate and is caused by fetal blood coursing through the umbilical cord, may also be heard, as well as the actual heartbeat of the fetus (see Fig. 8-8).

Cervical Changes.

In a normal, unscarred cervix, softening of the cervical tip may be observed about the beginning of the sixth week. This probable sign of pregnancy, Goodell sign, is brought about by increased vascularity, slight hypertrophy, and hyperplasia (increase in number of cells). The muscle and its collagen-rich connective tissue become loose, edematous, highly elastic, and increased in volume. The glands near the external os proliferate beneath the stratified squamous epithelium, giving the cervix the velvety appearance characteristic of pregnancy. Friability (tissue is easily damaged) is increased and can result in slight bleeding after vaginal examination or after coitus with deep penetration.

Pregnancy can also cause the squamocolumnar junction, the site for obtaining cells for cervical cancer screening, to be located away from the cervix. Because of these changes, evaluation of abnormal Papanicolaou (Pap) tests during pregnancy can be complicated. However, careful assessment of all pregnant women is important because approximately 3% of all invasive cervical cancers occur during pregnancy (Salani, Eisenhauer, and Copeland, 2012). The cervix of the nullipara is rounded. Lacerations of the cervix almost always occur during the birth process. After childbirth, with or without lacerations, the cervix becomes more oval in the horizontal plane and the external os appears as a transverse slit (see Fig. 7-2).

Changes Related to the Presence of the Fetus.

Passive movement of the unengaged fetus is called ballottement and can be identified generally between the sixteenth and eighteenth week. Ballottement is a technique of palpating a floating structure by bouncing it gently and feeling it rebound. To palpate the fetus, the examiner places a finger within the vagina and taps gently upward on the cervix, causing the fetus to rise. The fetus then sinks, and a gentle tap is felt on the finger.

The first recognition of fetal movements, or “feeling life,” by the multiparous woman may occur as early as 14 to 16 weeks. The nulliparous woman may not notice these sensations until the eighteenth week or later. Quickening is commonly described as a flutter and is difficult to distinguish from peristalsis. Fetal movements gradually increase in intensity and frequency as pregnancy progresses. The week in which quickening occurs provides a tentative clue in dating the duration of gestation.

Vagina and Vulva

Pregnancy hormones prepare the vagina for stretching during labor and birth by causing the vaginal mucosa to thicken, the connective tissue to loosen, the smooth muscle to hypertrophy, and the vaginal vault to lengthen. Increased vascularity results in a violet-bluish color of the vaginal mucosa and cervix. The deepened color, termed Chadwick sign, can be evident as early as the sixth week but is easily noted by the eighth week of pregnancy (Blackburn, 2013).

Leukorrhea is a white or slightly gray mucoid discharge with a faint musty odor. This copious mucoid fluid occurs in response to cervical stimulation by estrogen and progesterone. The fluid is whitish because of the presence of many exfoliated vaginal epithelial cells caused by the hyperplasia of normal pregnancy. This vaginal discharge is never pruritic or blood stained. The mucus fills the endocervical canal, resulting in the formation of the mucus plug (operculum) (Fig. 7-6). The operculum acts as a barrier against bacterial invasion during pregnancy.

During pregnancy, the pH of vaginal secretions is more acidic, ranging from about 3.5 to about 6.0 (nonpregnant, 4.0 to 5.0), because of increased production of lactic acid (Cunningham, Leveno, Bloom, et al., 2010). Although this acidic environment provides more protection from some organisms, the pregnant woman is more vulnerable to other infections, especially yeast infections, because the glycogen-rich environment of the vagina is more susceptible to Candida albicans (Duff, Sweet, and Edwards, 2009).

The increased vascularity of the vagina and other pelvic viscera results in a marked increase in sensitivity. The increased sensitivity may lead to a high degree of sexual interest and arousal, especially during the second trimester of pregnancy. The increased congestion, plus the relaxed walls of the blood vessels and the heavy uterus, may result in edema and varicosities of the vulva. The edema and varicosities usually resolve during the postpartum period.

External structures of the perineum are enlarged during pregnancy because of an increase in vasculature, hypertrophy of the perineal body, and deposition of fat (Fig. 7-7). The labia majora of nullipara women approximate (come together) and obscure the vaginal introitus; those of the parous woman separate and gape after childbirth and perineal or vaginal injury. See Fig. 7-2 for a comparison of the nullipara and the multipara in relation to the pregnant abdomen, vulva, and cervix.

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