Physiological Changes of pregnancy 1 Dr Maha Atout

Physiological Changes of pregnancy (1) Dr. Maha Atout

Introduction n Physiologic changes that occur during pregnancy are the basis for the signs and symptoms used to confirm a pregnancy. n They can be categorized as local (i. e. , confined to the reproductive organs) or systemic (i. e. , affecting the entire body). n For easy reference, Table 10. 3 summarizes the changes that occur during a typical 40 -week pregnancy.

Table 10. 3: Timetable for Physiologic Changes of Pregnancy

Reproductive System Changes Reproductive tract changes are those involving the uterus, ovaries, vagina, and breasts. Uterine Changes The most obvious alteration in a woman’s body during pregnancy is the increase in size of the uterus to accommodate the growing fetus. Over the 10 lunar months of pregnancy, the uterus increases in length, depth, width, weight, wall thickness, and volume.

Uterine Changes n Length grows from approximately 6. 5 cm to 32 cm. Depth increases from 2. 5 cm to 22 cm. Width expands from 4 cm to 24 cm. Weight increases from 50 g to 1, 000 g. n Early in pregnancy, the uterine wall thickens from about 1 cm to about 2 cm; toward the end of pregnancy, the wall thins to become supple and only about 0. 5 -cm thick. n The volume of the uterus increases from about 2 ml to more than 1, 000 ml. This makes it possible for a uterus to hold a 7 -lb (3, 175 -g) fetus plus 1, 000 ml of amniotic fluid for a total of about 4, 000 g.

Reproductive System Changes: Uterine Changes n This great uterine growth is due partly to formation of a few new muscle fibers in the uterine myometrium but principally to the stretching of existing muscle fibers (by the end of pregnancy, muscle fibers in the uterus, because of fibroblastic tissue that forms between them, are two to seven times longer than they were before pregnancy). n Because uterine fibers simply stretch during pregnancy and are not newly built, the uterus is able to return to its prepregnant state at the end of the pregnancy with little difficulty and almost no destruction of tissue (Edmonds, 2012).

Reproductive System Changes: Uterine Changes n By the end of the 12 th week of pregnancy, the uterus is large enough that it can be palpated as a firm globe under the abdominal wall, just above the symphysis pubis. n An important factor to assess regarding uterine growth at health care visits is its constant, steady, and predictable increase in size (Fig. 10. 2). n By the 20 th or 22 nd week of pregnancy, it typically reaches the level of the umbilicus. n By the 36 th week, it usually touches the xiphoid process and can make breathing difficult.

Figure 10. 2: Fundus height at various weeks of pregnancy

Reproductive System Changes: Uterine Changes n About 2 weeks before term (the 38 th week) for a primigravida , a woman in her first pregnancy, the fetal head settles into the pelvis and the uterus returns to the height it was at 36 weeks. n This settling of the fetus into the mid-pelvis is termed lightening , because a woman’s breathing is so much easier that she feels as if her load is lightened. n The point at which lightening will occur is not predictable in a multipara (a woman who has had one or more children). In such women, it may not occur until labor begins. Uterine height is measured from the top of the symphysis pubis to over the top of the uterine fundus (Zheng, 2012 a).

Reproductive System Changes: Uterine Changes n Although growth of a uterus implies a pregnancy is causing the increase in size, because a uterine tumor could also cause uterine growth, uterine growth is only a presumptive symptom of pregnancy. n The exact shape of the expanding uterus can be influenced by the position of the fetus. As the uterus grows larger, it pushes the intestines to the sides of the abdomen, elevates the diaphragm and liver, compresses the stomach, and puts pressure on the bladder).

Reproductive System Changes: Uterine Changes n It usually remains in the midline during pregnancy, although it may be pushed slightly to the right side because of the larger bulk of the sigmoid colon on the left. n A woman may worry there will not be enough room inside her abdomen for this much increase in size. You can assure her the abdominal contents will readily shift to accommodate uterine enlargement (Fig. 10. 3). Uterine blood flow increases during pregnancy as the placenta requires more and more blood for perfusion.

Figure 10. 3 : Crowding of abdominal contents late in pregnancy

Reproductive System Changes: Uterine Changes n Doppler ultrasonography has shown that, before pregnancy, uterine blood flow is 15 to 20 ml/min. By the end of pregnancy, it expands to as much as 500 to 750 ml/min, with 75% of that volume going to the placenta. n Measuring an increase in placenta blood volume and velocity is an important gauge of fetal health (Cheema, Bayoumi, & Gudmundsson, 2011). n Circulation to the uterus increases so much that, toward the end of pregnancy, one sixth of a woman’s blood supply is circulating through the uterus at any given time;

Reproductive System Changes: Uterine Changes n This means uterine bleeding in pregnancy has to always be regarded as serious because it could result in sudden and major blood loss. Caution women to contact their health care provider if any vaginal bleeding occurs during pregnancy. n A bimanual examination (one finger of an examiner is placed in the vagina, the other hand on the abdomen) can demonstrate, during a pregnancy, that the uterus feels more ante-flexed, larger, and softer to the touch than usual.

Reproductive System Changes: Uterine Changes n At about the sixth week of pregnancy (at the time of the second missed menstrual flow), the lower uterine segment just above the cervix becomes so soft when it is compressed between examining fingers on bimanual examination that the wall feels as thin as tissue paper (Russell et al. , 2011). This extreme softening of the lower uterine segment is known as Hegar’s sign (Fig. 10. 4). n During the 16 th to 20 th week of pregnancy, when the fetus is still small in relation to the amount of amniotic fluid present, if the lower uterine segment is tapped sharply during a pelvic exam, the fetus can be felt to bounce or rise in the amniotic fluid up against a hand placed on the abdomen.

Figure 10. 4 : Examining for Hegar’s sign. If the sign is present, the wall of the uterus is softer than usual.

Reproductive System Changes: Uterine Changes n This phenomenon, termed ballottement (from the French word ballotter , meaning “to quake”), may, however, also be simulated by a loosely attached uterine tumor and, therefore, is no more than a probable sign of pregnancy. n Between the 20 th and 24 th week of pregnancy, the uterine wall becomes thinned to such a degree a fetal outline within the uterus may be palpated by a skilled examiner. Because a tumor with calcium deposits could simulate a fetal outline, palpation of what seems to be a fetus, like other uterine assessments, does not constitute a sure confirmation of pregnancy.

Reproductive System Changes: Uterine Changes n Uterine contractions begin early in pregnancy, at least by the 12 th week, and are present throughout the rest of pregnancy, becoming stronger and harder as the pregnancy ad vances. A woman experiences them as waves of hardness or tightening across her abdomen. n If a hand is placed on her abdomen, an examiner may be able to feel these contractions as well; an electronic monitor can easily measure both the frequency and length of such contractions. These “practice” contractions, termed Braxton Hicks contractions , serve as warm-up exercises for labor and also play a role in ensuring the placenta receives adequate blood.

Reproductive System Changes: Uterine Changes n They may become so strong in the last month of pregnancy that a woman mistakes them for labor contractions (i. e. , false labor). n One way they can be differentiated from true contractions is that true contractions cause cervical dilation, and Braxton Hicks contractions do not (Attilakos & Overton, 2012). n Although these contractions are always present with pregnancy, they also could accompany growing uterine mass; so, like ballottement, they are no more than a probable sign of pregnancy.

Uterine Changes: Amenorrhea n Amenorrhea (i. e. , an absence of a menstrual flow) occurs with pregnancy because of the suppression of folliclestimulating hormone (FSH) by rising estrogen levels. In a healthy woman who has menstruated previously, the absence of a menstrual flow strongly suggests impregnation has occurred. n Amenorrhea, however, also heralds the onset of menopause or could result from unrelated reasons such as uterine infection, anxiety (perhaps over becoming pregnant), a chronic illness such as severe anemia, or undue stress.

Uterine Changes: Amenorrhea n It also is seen in athletes who train strenuously, especially in long-distance runners and ballet dancers if their body fat percentage drops below a critical point (Doyle-Lucas, Akers, & Davy, 2010). Amenorrhea is, therefore, only a presumptive symptom of pregnancy

Cervical Changes n In response to the increased level of circulating estrogen produced by the placenta during pregnancy, the cervix of the uterus becomes more vascular and edematous than usual. n A mucous plug, called the operculum , forms to seal out bacteria and help prevent infection in the fetus and membranes. n Increased fluid between cells causes it to soften in consistency, and increased vascularity causes it to darken from a pale pink to a violet hue ( Goodell’s sign ).

Cervical Changes n The consistency of a non-pregnant cervix can be compared with that of the nose; the consistency of a pregnant cervix more closely resembles an earlobe. n Just before labor, the cervix becomes so soft it takes on the consistency of butter or is said to be “ripe” for birth (Aguirre & Chou, 2011).

Vaginal Changes n Under the influence of estrogen, the vaginal epithelium and underlying tissues increase in size as they become enriched with glycogen. n Muscle fibers loosen from their connective tissue base in preparation for great distention at birth. This increase in the activity of the epithelial cells results in a slight white vaginal discharge throughout pregnancy (but this is only a presumptive symptom as vaginal infections also produce discharges).

Vaginal Changes n An increase in the vascularity of the vagina parallels the vascular changes in the uterus. n The resulting increase in circulation changes the color of the vaginal walls from their normal light pink to a deep violet ( Chadwick’s sign ). n Vaginal secretions before pregnancy have a p. H value greater than 7 (an alkaline p. H). During pregnancy, the p. H level falls to 4 or 5 (an acid p. H), which helps make the vagina resistant to bacterial invasion for the length of the pregnancy.

Vaginal Changes n This occurs because of the action of Lactobacillus acidophilus, a bacteria that grows freely in the increased glycogen environment, which increases the lactic acid content of secretions.

Ovarian Changes n Ovulation stops with pregnancy because of the active feedback mechanism of estrogen and progesterone produced early in pregnancy by the corpus luteum and late in pregnancy by the placenta. n This feedback causes the pituitary gland to halt production of FSH and luteinizing hormone (LH); without stimulation from FSH and LH, ovulation does not occur. n The corpus luteum that was created after ovulation continues to increase in size on the surface of the ovary until about the 16 th week of pregnancy, by which time the placenta takes over as the chief provider of progesterone and estrogen.

Ovarian Changes n The corpus luteum, no longer essential for the continuation of the pregnancy, regresses in size and appears white and fibrous on the surface of the ovary (a corpus albicans).

Changes in the Breasts n Changes in the Breasts Subtle changes in the breasts may be one of the first physiologic changes of pregnancy a woman notices (at about 6 weeks) (Fig. 10. 5). n Typical changes are a feeling of fullness, tingling, or tenderness that occurs because of the increased stimulation of breast tissue by the high estrogen level in her body. n As the pregnancy progresses, breast size increases because of growth in the mammary alveoli and in fat deposits.

Figure 10. 5: Comparison of non-pregnant and pregnant breasts.

Changes in the Breasts n The areola of the nipple darkens, and its diameter increases from about 3. 5 cm (1. 5 in. ) to 5 cm or 7. 5 cm (2 or 3 in. ). n There is additional darkening of the skin surrounding the areola in some women, forming a secondary areola. Early in pregnancy, the breasts begin readying themselves for the secretion of milk. n By the 16 th week, colostrum—the thin, watery, highprotein fluid that is the precursor of breast milk—can be expelled from the nipples.

Changes in the Breasts n As vascularity of the breasts increases, blue veins may become prominent over the surface of the breasts. The sebaceous glands of the areola (Montgomery’s tubercles) , which keep the nipple supple and help to prevent nipples from cracking and drying during lactation, enlarge and become protuberant. n Talking to women during pregnancy about breast changes and how these changes are devised to aid breastfeeding can be the trigger that alerts women to the importance of breastfeed-ing for their baby (Baselice & Lawson, 2011).