What Changes During Fever And Menstruation, And Which Hormone Causes This Change?

Learning Objectives

By the finish of this section, yous will be able to:

• Explain how estrogen, progesterone, and hCG are involved in maintaining pregnancy
• List the contributors to weight gain during pregnancy
• Describe the major changes to the maternal digestive, circulatory, and integumentary systems during pregnancy
• Summarize the events leading to labor
• Place and describe each of the 3 stages of childbirth

A total-term pregnancy lasts approximately 270 days (approximately 38.5 weeks) from conception to nativity. Because information technology is easier to retrieve the first twenty-four hours of the last menstrual period (LMP) than to estimate the date of conception, obstetricians set the due date as 284 days (approximately twoscore.five weeks) from the LMP. This assumes that formulation occurred on day fourteen of the adult female's cycle, which is ordinarily a skilful approximation. The 40 weeks of an average pregnancy are usually discussed in terms of 3 trimesters, each approximately 13 weeks. During the second and third trimesters, the pre-pregnancy uterus—about the size of a fist—grows dramatically to contain the fetus, causing a number of anatomical changes in the mother ([link]).

Figure 28.xviii Size of Uterus throughout Pregnancy The uterus grows throughout pregnancy to accommodate the fetus.

Effects of Hormones

Most all of the effects of pregnancy can be attributed in some way to the influence of hormones—specially estrogens, progesterone, and hCG. During weeks 7–12 from the LMP, the pregnancy hormones are primarily generated by the corpus luteum. Progesterone secreted by the corpus luteum stimulates the production of decidual cells of the endometrium that nourish the blastocyst before placentation. As the placenta develops and the corpus luteum degenerates during weeks 12–17, the placenta gradually takes over as the endocrine organ of pregnancy.

The placenta converts weak androgens secreted by the maternal and fetal adrenal glands to estrogens, which are necessary for pregnancy to progress. Estrogen levels climb throughout the pregnancy, increasing xxx-fold by childbirth. Estrogens have the following actions:

• They suppress FSH and LH production, effectively preventing ovulation. (This function is the biological basis of hormonal birth control pills.)
• They induce the growth of fetal tissues and are necessary for the maturation of the fetal lungs and liver.
• They promote fetal viability by regulating progesterone production and triggering fetal synthesis of cortisol, which helps with the maturation of the lungs, liver, and endocrine organs such as the thyroid gland and adrenal gland.
• They stimulate maternal tissue growth, leading to uterine enlargement and mammary duct expansion and branching.

Relaxin, another hormone secreted by the corpus luteum and then by the placenta, helps prepare the female parent's body for childbirth. It increases the elasticity of the symphysis pubis joint and pelvic ligaments, making room for the growing fetus and allowing expansion of the pelvic outlet for childbirth. Relaxin too helps dilate the cervix during labor.

The placenta takes over the synthesis and secretion of progesterone throughout pregnancy as the corpus luteum degenerates. Similar estrogen, progesterone suppresses FSH and LH. It also inhibits uterine contractions, protecting the fetus from preterm nascency. This hormone decreases in late gestation, assuasive uterine contractions to intensify and somewhen progress to truthful labor. The placenta also produces hCG. In improver to promoting survival of the corpus luteum, hCG stimulates the male fetal gonads to secrete testosterone, which is essential for the development of the male reproductive system.

The anterior pituitary enlarges and ramps up its hormone production during pregnancy, raising the levels of thyrotropin, prolactin, and adrenocorticotropic hormone (ACTH). Thyrotropin, in conjunction with placental hormones, increases the production of thyroid hormone, which raises the maternal metabolic rate. This can markedly augment a pregnant woman'due south ambition and cause hot flashes. Prolactin stimulates enlargement of the mammary glands in preparation for milk production. ACTH stimulates maternal cortisol secretion, which contributes to fetal poly peptide synthesis. In add-on to the pituitary hormones, increased parathyroid levels mobilize calcium from maternal basic for fetal use.

Weight Proceeds

The second and third trimesters of pregnancy are associated with dramatic changes in maternal anatomy and physiology. The near obvious anatomical sign of pregnancy is the dramatic enlargement of the abdominal region, coupled with maternal weight gain. This weight results from the growing fetus besides equally the enlarged uterus, amniotic fluid, and placenta. Boosted breast tissue and dramatically increased blood volume also contribute to weight gain ([link]). Surprisingly, fatty storage accounts for only approximately 2.iii kg (5 lbs) in a normal pregnancy and serves as a reserve for the increased metabolic demand of breastfeeding.

During the first trimester, the mother does not need to consume additional calories to maintain a healthy pregnancy. Withal, a weight proceeds of approximately 0.45 kg (i lb) per month is common. During the second and third trimesters, the mother'southward appetite increases, merely information technology is only necessary for her to consume an additional 300 calories per day to back up the growing fetus. About women proceeds approximately 0.45 kg (one lb) per week.

Contributors to Weight Gain During Pregnancy

Component	Weight (kg)	Weight (lb)
Fetus	three.2–3.six	7–8
Placenta and fetal membranes	0.9–1.8	ii–4
Amniotic fluid	0.9–i.four	ii–3
Breast tissue	0.ix–1.four	2–iii
Claret	i.4	4
Fat	0.ix–4.1	iii–ix
Uterus	0.9–2.iii	ii–5
Total	10–16.3	22–36

Table 28.2

Changes in Organ Systems During Pregnancy

Equally the adult female's body adapts to pregnancy, characteristic physiologic changes occur. These changes can sometimes prompt symptoms often referred to collectively as the common discomforts of pregnancy.

Digestive and Urinary Organization Changes

Nausea and vomiting, sometimes triggered by an increased sensitivity to odors, are common during the starting time few weeks to months of pregnancy. This phenomenon is oftentimes referred to every bit "forenoon sickness," although the nausea may persist all solar day. The source of pregnancy nausea is thought to be the increased circulation of pregnancy-related hormones, specifically circulating estrogen, progesterone, and hCG. Decreased intestinal peristalsis may also contribute to nausea. Past about week 12 of pregnancy, nausea typically subsides.

A common gastrointestinal complaint during the afterward stages of pregnancy is gastric reflux, or heartburn, which results from the upwards, constrictive pressure level of the growing uterus on the tummy. The same decreased peristalsis that may contribute to nausea in early pregnancy is also idea to be responsible for pregnancy-related constipation as pregnancy progresses.

The downwardly pressure of the uterus besides compresses the urinary bladder, leading to frequent urination. The problem is exacerbated by increased urine product. In addition, the maternal urinary organisation processes both maternal and fetal wastes, further increasing the total volume of urine.

Circulatory System Changes

Blood volume increases substantially during pregnancy, and so that by childbirth, it exceeds its preconception book past 30 per centum, or approximately 1–2 liters. The greater blood volume helps to manage the demands of fetal nourishment and fetal waste removal. In conjunction with increased blood volume, the pulse and blood force per unit area besides rise moderately during pregnancy. As the fetus grows, the uterus compresses underlying pelvic blood vessels, hampering venous render from the legs and pelvic region. As a issue, many significant women develop varicose veins or hemorrhoids.

Respiratory Arrangement Changes

During the second half of pregnancy, the respiratory minute volume (book of gas inhaled or exhaled by the lungs per minute) increases by 50 percent to recoup for the oxygen demands of the fetus and the increased maternal metabolic charge per unit. The growing uterus exerts upward force per unit area on the diaphragm, decreasing the book of each inspiration and potentially causing shortness of breath, or dyspnea. During the last several weeks of pregnancy, the pelvis becomes more than rubberband, and the fetus descends lower in a process called lightening. This typically ameliorates dyspnea.

The respiratory mucosa swell in response to increased blood flow during pregnancy, leading to nasal congestion and nose bleeds, particularly when the weather is cold and dry. Humidifier employ and increased fluid intake are frequently recommended to counteract congestion.

Integumentary System Changes

The dermis stretches extensively to accommodate the growing uterus, chest tissue, and fat deposits on the thighs and hips. Torn connective tissue beneath the dermis can cause striae (stretch marks) on the belly, which announced equally red or imperial marks during pregnancy that fade to a silvery white color in the months after childbirth.

An increase in melanocyte-stimulating hormone, in conjunction with estrogens, darkens the areolae and creates a line of paint from the navel to the pubis called the linea nigra ([link]). Melanin production during pregnancy may too darken or discolor skin on the face to create a chloasma, or "mask of pregnancy."

Figure 28.19 Linea Nigra The linea nigra, a night medial line running from the belly button to the pubis, forms during pregnancy and persists for a few weeks following childbirth. The linea nigra shown here corresponds to a pregnancy that is 22 weeks along.

Physiology of Labor

Childbirth, or parturition, typically occurs inside a week of a woman's due engagement, unless the woman is pregnant with more than one fetus, which usually causes her to go into labor early. As a pregnancy progresses into its final weeks, several physiological changes occur in response to hormones that trigger labor.

First, recollect that progesterone inhibits uterine contractions throughout the first several months of pregnancy. As the pregnancy enters its 7th month, progesterone levels plateau so driblet. Estrogen levels, however, continue to rise in the maternal apportionment ([link]). The increasing ratio of estrogen to progesterone makes the myometrium (the uterine smooth muscle) more sensitive to stimuli that promote contractions (considering progesterone no longer inhibits them). Moreover, in the eighth month of pregnancy, fetal cortisol rises, which boosts estrogen secretion by the placenta and further overpowers the uterine-calming effects of progesterone. Some women may feel the result of the decreasing levels of progesterone in tardily pregnancy every bit weak and irregular peristaltic Braxton Hicks contractions, besides chosen false labor. These contractions tin can often be relieved with rest or hydration.

Figure 28.20 Hormones Initiating Labor A positive feedback loop of hormones works to initiate labor.

A common sign that labor volition exist short is the and then-called "bloody evidence." During pregnancy, a plug of fungus accumulates in the cervical culvert, blocking the entrance to the uterus. Approximately 1–2 days prior to the onset of truthful labor, this plug loosens and is expelled, forth with a small amount of blood.

Meanwhile, the posterior pituitary has been boosting its secretion of oxytocin, a hormone that stimulates the contractions of labor. At the same time, the myometrium increases its sensitivity to oxytocin by expressing more than receptors for this hormone. As labor nears, oxytocin begins to stimulate stronger, more painful uterine contractions, which—in a positive feedback loop—stimulate the secretion of prostaglandins from fetal membranes. Similar oxytocin, prostaglandins also enhance uterine contractile forcefulness. The fetal pituitary also secretes oxytocin, which increases prostaglandins even further. Given the importance of oxytocin and prostaglandins to the initiation and maintenance of labor, it is not surprising that, when a pregnancy is not progressing to labor and needs to be induced, a pharmaceutical version of these compounds (called pitocin) is administered by intravenous baste.

Finally, stretching of the myometrium and cervix by a full-term fetus in the vertex (head-down) position is regarded as a stimulant to uterine contractions. The sum of these changes initiates the regular contractions known as true labor, which become more than powerful and more frequent with fourth dimension. The pain of labor is attributed to myometrial hypoxia during uterine contractions.

Stages of Childbirth

The process of childbirth tin exist divided into three stages: cervical dilation, expulsion of the newborn, and afterbirth ([link]).

Cervical Dilation

For vaginal birth to occur, the neck must dilate fully to 10 cm in bore—wide enough to evangelize the newborn's caput. The dilation phase is the longest stage of labor and typically takes 6–12 hours. However, information technology varies widely and may have minutes, hours, or days, depending in function on whether the mother has given nativity before; in each subsequent labor, this stage tends to be shorter.

Figure 28.21 Stages of Childbirth The stages of childbirth include Stage 1, early cervical dilation; Phase ii, full dilation and expulsion of the newborn; and Stage 3, delivery of the placenta and associated fetal membranes. (The position of the newborn's shoulder is described relative to the female parent.)

True labor progresses in a positive feedback loop in which uterine contractions stretch the cervix, causing it to dilate and efface, or become thinner. Cervical stretching induces reflexive uterine contractions that dilate and efface the cervix farther. In improver, cervical dilation boosts oxytocin secretion from the pituitary, which in plow triggers more powerful uterine contractions. When labor begins, uterine contractions may occur only every iii–30 minutes and final only twenty–xl seconds; however, by the cease of this stage, contractions may occur as ofttimes as every 1.5–2 minutes and last for a full infinitesimal.

Each contraction sharply reduces oxygenated blood flow to the fetus. For this reason, it is critical that a period of relaxation occur after each contraction. Fetal distress, measured as a sustained decrease or increase in the fetal centre charge per unit, can issue from severe contractions that are too powerful or lengthy for oxygenated blood to exist restored to the fetus. Such a state of affairs tin be crusade for an emergency nativity with vacuum, forceps, or surgically by Caesarian section.

The amniotic membranes rupture before the onset of labor in about 12 pct of women; they typically rupture at the end of the dilation stage in response to excessive pressure from the fetal head entering the birth canal.

Expulsion Stage

The expulsion phase begins when the fetal head enters the birth canal and ends with birth of the newborn. Information technology typically takes upwardly to 2 hours, simply information technology tin last longer or be completed in minutes, depending in part on the orientation of the fetus. The vertex presentation known as the occiput inductive vertex is the most mutual presentation and is associated with the greatest ease of vaginal birth. The fetus faces the maternal spinal string and the smallest role of the head (the posterior aspect called the occiput) exits the birth canal kickoff.

In fewer than 5 percent of births, the infant is oriented in the breech presentation, or buttocks down. In a complete breech, both legs are crossed and oriented downward. In a frank breech presentation, the legs are oriented upward. Before the 1960s, it was common for breech presentations to be delivered vaginally. Today, well-nigh breech births are accomplished by Caesarian section.

Vaginal birth is associated with significant stretching of the vaginal canal, the cervix, and the perineum. Until recent decades, it was routine procedure for an obstetrician to numb the perineum and perform an episiotomy, an incision in the posterior vaginal wall and perineum. The perineum is now more than normally allowed to tear on its own during birth. Both an episiotomy and a perineal tear need to exist sutured shortly after nascency to ensure optimal healing. Although suturing the jagged edges of a perineal tear may be more difficult than suturing an episiotomy, tears heal more quickly, are less painful, and are associated with less damage to the muscles around the vagina and rectum.

Upon nascence of the newborn'southward head, an obstetrician will aspirate fungus from the oral cavity and nose earlier the newborn's first breath. Once the caput is birthed, the balance of the body commonly follows quickly. The umbilical cord is and so double-clamped, and a cut is made between the clamps. This completes the second stage of childbirth.

Afterbirth

The commitment of the placenta and associated membranes, commonly referred to as the afterbirth, marks the final phase of childbirth. Afterwards expulsion of the newborn, the myometrium continues to contract. This move shears the placenta from the back of the uterine wall. Information technology is then easily delivered through the vagina. Continued uterine contractions then reduce claret loss from the site of the placenta. Delivery of the placenta marks the commencement of the postpartum menstruum—the period of approximately six weeks immediately following childbirth during which the mother's body gradually returns to a non-pregnant land. If the placenta does not birth spontaneously within approximately thirty minutes, it is considered retained, and the obstetrician may attempt transmission removal. If this is not successful, surgery may be required.

It is important that the obstetrician examines the expelled placenta and fetal membranes to ensure that they are intact. If fragments of the placenta remain in the uterus, they can cause postpartum hemorrhage. Uterine contractions continue for several hours after nascence to return the uterus to its pre-pregnancy size in a process called involution, which also allows the mother's abdominal organs to return to their pre-pregnancy locations. Breastfeeding facilitates this procedure.

Although postpartum uterine contractions limit blood loss from the detachment of the placenta, the mother does feel a postpartum vaginal discharge called lochia. This is made up of uterine lining cells, erythrocytes, leukocytes, and other debris. Thick, dark, lochia rubra (red lochia) typically continues for 2–iii days, and is replaced by lochia serosa, a thinner, pinkish form that continues until about the 10th postpartum day. After this menstruation, a scant, creamy, or watery discharge called lochia alba (white lochia) may continue for some other 1–2 weeks.

Source: https://openstax.org/books/anatomy-and-physiology/pages/28-4-maternal-changes-during-pregnancy-labor-and-birth

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