Unit 4 - Labor and Birth

Passageway

Consists of the woman's bony pelvis and soft tissues of the cervix and vagina.

Oxytocin theory

Another hypothesis regarding the cause of labor. Because the hormone oxytocin causes the uterus to contract, some scientists have proposed that the rice in oxytocin levels may be responsible for initiating labor. However, blood levels of oxytocin do not measurably increase before labor begins; therefore, some researchers have concluded that oxytocin is probably not the main factor that stimulates labor to begin.

Anticipatory signs of Labor

Approximately 2 weeks before labor, the presenting part may settle into the pelvic cavity, causing the pregnant woman to sense that the baby has "dropped." This subjective feeling is called "lightening." The woman is able to breathe more easily and may need to urinate more frequently because of the pressure of the fetus on the urinary bladder. Braxton Hicks contractions occur more frequently and are more noticeable as pregnancy approaches term. These irregular, practice contractions usually decrease in intensity while walking and position changes. The woman may experience gastrointestinal disturbances, such as diarrhea, heartburn, or nausea and vomiting as labor approaches. Sometimes the mucus plug is expelled a week or two before labor begins. When the mucus plug passes, the woman will notice a one time clear or pink-tinged discharge that is the consistency of jelly. She may have a burst of energy 24-48 hours before the onset of labor and may also have the desire to do heavy cleaning or some other big project in anticipation for the baby's arrival, a phenomenon known as the nesting urge. Caution the woman regarding the nesting urge, and advise her to conserve her energy for the work of labor. Clinical signs that labor is approaching include ripening or softening and effacement (thinning) of the cervix. Dilation of the cervix may accompany softening and effacement, particularly in multiparous women. The practitioner will inform the woman of these changes when a pelvic exam is done during the scheduled office visit.

Cascade

Because a single causative factor of labor initiation has not yet been determined, the most likely answer seems to be that labor results from a combination of maternal and fetal factors working together in a cascade effect. During the cascade, factors that inhibit contractions, such as progesterone, are suppressed, and factors that promote contractions, such as prostaglandins are engaged.

Fourth stage: Recovery

Because of the tremendous changes that the new mother's body goes through during the process of labor and delivery, the period of recovery after deliver of the placenta is considered to be the fourth stage of labor. This recovery stage may last from one to four hours, during which the woman should be observed frequently for signs of hemorrhage or other complications.

Factors that may affect Maternal Psyche

Current Pregnancy experience - Unplanned versus planned pregnancy, amount of difficulty conceiving, presence of risk factors or complications of pregnancy Previous birth experiences - Positive or negative feelings regarding previous delivery experience, complications encountered during previous delivery, mode of delivery (vaginal versus cesarean), birth outcomes (e.g., fetal demise, birth defects) Expectations for current birth experience - View of labor as a meaningful or stressful event, realistic and attainable goals versus idealistic views that conflict with reality (a situation that can lead to disappointment) Preparation for birth - Type of childbirth preparation, familiarity with institution and its policies and procedures, type of relaxation techniques learned and practiced Presence and support of a birth companion Culture - A woman's culture influences and defines: The childbirth experience - shameful versus joyful, superstitions and beliefs about pregnancy and birth, prescribed behaviors and taboos during the intrapartum period. Relationships - Interpersonal interactions, parent-infant interactions, role expectations of family members, support person involvement Pain - Meaning and context of pain during labor, acceptable responses to pain during labor The significance of touch - Soothing versus intruding, May be a symbol of intimacy.

Difference between false and true labor

False labor (prodromal labor) refers to the increase in braxton hicks contractions that occur toward the end of pregnancy. These practice contractions can be quite uncomfortable, making it difficult to distinguish true labor from false labor. When a woman presents to the labor suite because she thinks she is in labor the nursing staff will perform an initial assessment and barring any risk factors, instruct the woman to walk for an hour or two. Then a vaginal exam is performed to determine any cervical changes. If there are any changes the practitioner diagnoses true labor and admits the laboring woman to the hospital. If there is not, then the woman may be instructed to go home and return if the contractions become stronger, more regular, or if other signs of true labor occur, such as increased bloody show or rupture of the membranes.

Fetal Attitude

Fetal attitude refers to the relationship of the fetal parts to one another. In a cephalic presentation, there are several different ways the head can present to the maternal pelvis, depending on fetal attitude. The most common attitude, and the one most favorable for a vaginal birth, is an attitude of flexion, also called a vertex presentation (Fetus presents curled up into an ovoid shape and has the smallest diameters of the skull to the bony pelvis). When the fetus is neither flexed nor hyperextended, he or she is in the military presentation and a larger head diameter presents. If the fetus's neck is partially extended, the brow (or frontum) becomes the presenting part. When the fetus's neck is fully extended, the face presents.

Fetal Lie

Fetal lie describes the position of the long axis in relation to the long axis of the pregnant woman. There are three basic ways a fetus lie in the uterus: in a longitudinal, transverse, or oblique position. A longitudinal lie, in which the long axis of the fetus is parallel to the long axis of the mother is most common. A transverse lie is when the long axis of the fetus is perpendicular to the long axis of the mother. An oblique lie is in between the two.

Stages and duration of labor

Labor is categorized into four stages and the first stage is further separated into three phases. It is important to note that individual labors vary greatly with regard to length. Many factors affect the progress of labor such as parity, the use of agents to soften the cervix, labor induction techniques, and type of anesthesia (if any) used.

Passenger

Refers to the fetus. The size of the fetal skull and fetal accommodation to the passageway (i.e., fetal lie, presentation, attitude, position, and station) can significantly affect labor progress.

Psyche

Many factors affect the psychological state or psyche of the laboring woman. When the woman feels confident in her ability to cope and finds way to work with the contractions, the labor process is enhanced. However, if the laboring woman becomes fearful or has intense pain, she may become tense and fight the contractions. This situation often becomes a cycle of fear, tension, and pain that interferes with the progress of labor.

Fetal Presentation

Refers to the foremost part of the fetus that enters the pelvic inlet. There are three main ways the fetus can present to the pelvis: head (cephalic presentation), feet or buttocks (breech presentation), or shoulder (shoulder presentation). Most fetuses (95%) are in a cephalic presentation at the end of pregnancy. Breech presentations occur in approximately 3% of term pregnancies. Should presentations, the least common, occur in less than 0.3% of all term pregnancies and is usually associated with a transverse lie.

Fetal Adaptations to labor

Normal labor stresses the fetus in several ways. Intracranial pressure increases as the fetal head meets resistance from the birth canal. Sometimes this increased pressure results in a slowing of the fetal heart rate at the peak of a contraction. Placental blood flow, the source of the oxygen for the fetus, is temporarily interrupted at the peak of each contraction. Because of the changes, even the healthy fetus experiences a decreasing pH throughout labor. If Fetal pH is >7.25 it is reassuring and associated with normal acid-base balance. If it is between 7.20 and 7.25 it is worrisome and may be associated with metabolic acidosis. If it is <7.20 it is critical and represents metabolic acidosis. And if it is <7 it is damaging and frequently associated with fetal neurologic damage. Although labor stresses the fetal cardiovascular system, a healthy fetus is able to compensate and maintain the heart rate within normal limits. This ability to compensate demonstrates the presence of a well-oxygenated fetus with a healthy neurologic system. The act of passing through the birth canal is beneficial to the fetus in two ways. The process of labor stimulates surfactant production to promote respiratory adaptation at birth, and as the fetus descends, maternal tissues compress the body, a process that helps clear the respiratory passageways of mucus. Infants who are born by cesarean section usually require more frequent suctioning because they have not had the benefit of this "vaginal squeeze." Pressure on the fetus caused by progress through the birth canal may result in areas of ecchymosis or edema, particularly on the presenting part. Pressure on the vertex may cause the formation of a caput succedaneum (swelling of the soft tissue of the head) or development of a cephalohematoma (collection of blood under the scalp).

Pelvic Dimensions

Particularly if the woman has never delivered a baby vaginally, the practitioner may take pelvic measurements to estimate the size of the true pelvis. However these measurements don't consistently predict which women will have difficulty delivering vaginally so most practitioners will allow the woman to labor and attempt a vaginal birth. The most important measurement of the inlet is the obstetric conjugate because it is the smallest diameter of the inlet through which the fetus must pass. However the obstetric conjugate cannot be measured directly and therefore the practitioner must estimate the size. To obtain this estimate, the practitioner measures the diagonal conjugate, which extends from the symphysis pubis to the sacral promontory. The practitioner then subtracts 1.5 to 2cm from the measurement of the diagonal conjugate to approximate the dimensions of the obstetric conjugate. An obstetric conjugate that measures 11 cm is considered adequate to accommodate a vaginal delivery. The practitioner takes measurements of the midpelvis at the level of the ischial spines. If the ischial spines are prominent and extended into the midpelvis they can reduce the diameter of the midpelvis and might interfere with the journey of the fetus through the passageway during labor. One important measurement of the outlet is the angle of the pubic arch. This angle should be at least 90 degrees. (Just because the inlet and outlet are adequate for delivery does not mean that the midpelvis is adequate)

Four "P's" of Labor

Passageway, Passenger, Power, and Psyche

The prostaglandin theory

Prostaglandins influence labor in several ways, which include softening the cervix and stimulating the uterus to contract. However, evidence supporting the theory that prostaglandins are the agents that trigger labor to begin are inconclusive.

Third Stage: Delivery of the Placenta

Stage 3 begins with the birth of the baby and ends with the delivery of the placenta. This stage normally lasts for 20 minutes for both primiparas and multiparas. Signs that indicate the placenta is separating from the uterine wall include a gush of blood, lengthening of the umbilical cord, and a globular shape to the fundus. The placenta usually delivers spontaneously by one of two mechanisms. Expulsion by the Schultze mechanism means that the fetal or shiny side of the placenta delivers first. Delivery by the Duncan mechanism specifies that the maternal or rough side of the placenta presents first.

Fetal Station

Station refers to the relationship of the presenting fetus to the ischial spines of the pelvis. When the widest diameter of the present part is at the level of the ischial spines, the station is zero(0). If the presenting part is above the level of the ischial spines the station is recorded as having a negative number and is read "minus." If the presenting part is below the level of the ischial spines it is recorded as a positive number and read "plus." (Example - In a cephalic presentation, if the widest part of the fetal head is 1 cm above the level of the ischial spines, the station is reported as a minus one and recorded as -1. If on the other hand it is 1 cm below the ischial spines, it is reported plus one and recorded +1.) When the station is minus four (-4) or higher, the fetus is said to be floating and unengaged. When the fetus is floating the presenting part has yet to enter the true pelvis. When the presenting part has settled into the true pelvis at the level of the ischial spines, the fetus is said to be engaged and is reported to be at a station of zero (0). When the fetus is being born it is said to be at station plus four (+4).

Progesterone withdrawal theory

Suggests that if progesterone (the hormone of pregnancy) is withdrawn, the uterus will begin to contract, the uterus lining will begin to slough, and labor will result. However progesterone levels do not fall before labor so this theory does not explain what causes labor to begin.

Chapter 8

The Labor Process

Soft Tissues

The cervix and vagina are soft tissues that form the part of the passageway known as the birth canal. In early pregnancy the cervix is long, firm, and closed. As the time for delivery approaches, the cervix usually begins to soften. Then when labor begins uterine contractions affect the cervix in two ways. First, the cervix begins to get shorter and thinner, a process called effacement. Cervical effacement is recorded as a percentage. The cervical canal measures approximately 2 cm before effacement. At a length of 1 cm, the cervix is 50% effaced. When the cervix is paper thin, it is 100% effaced. The second cervical change that occurs during normal labor is dilation. The cervix must open to allow the fetus to be born. Dilation is measured in centimeters and is considered completely dilated at 10 cm. Normally a primiparous woman experiences effacement before dilation while for a multiparous woman, both processes usually occur at the same time. Often the multipara's cervix dilates 1 to 2 cm several weeks before labor begins. The vaginal canal participates in childbirth via passive distention. During birth, the rugae of the vaginal walls stretch and smooth out, allowing for considerable expansion. The muscles and soft tissues of the primipara provide greater resistance to stretching and distending than those of the multipara. This is one reason why the first baby often takes longer to be born than subsequent babies.

Fetal position

The fetal position is determined by comparing the relationship of an arbitrarily determined reference point on the presenting part of the fetus to the quadrants of the maternal pelvis. To determine position, first establish the presenting part and locate the appropriate reference point. then determine which pelvic quadrant the reference point is facing. Designations go into three parts (letters). The first designation is the side of the maternal pelvis in which the presenting part is found and or facing. It can be Right (R) or Left (L). The second designation is the reference point on the presenting part. Occiput (O) is the reference point for vertex and military presentations. Frontum or brow (Fr) is the reference point for brow presentation. Mentum or chin (M) is the reference point for face presentation. Sacrum (S) is the reference point for breech presentation. Scapula (Sc) is the reference point for shoulder presentation. The last designation refers to where on the maternal pelvis the reference point is found. Anterior (A) front of the pelvis, Posterior (P) is the back of the pelvis, and Transverse (T) is the side of the pelvis. For Example a Reference point of a chin, found facing the left side on the transverse side of the pelvis would be a LMT. The most favorable positions for vaginal birth are occiput anterior, either ROA or LOA.

First Stage : Dilation

The first stage of labor begins with the onset of true labor and ends with full dilation of the cervix at 10 cm. This stage is divided into three phases: latent, active and transition. Early Labor (Latent Phase) Begins when contractions of true labor start and ends when the cervix is dilated 4 cm. Contractions are usually mild intensity and typically occur at a frequency of five to ten minutes (although they can occur as infrequently as every 30 minutes) with a duration of 30 to 45 seconds. In a normal labor, the pattern of contractions during the latent phase becomes increasingly regular with shorter intervals between contractions. The latent phase lasts on average approximately eight to nine hours for a primiparous woman but generally does not exceed 20 hours in length. Multiparous women usually experience shorter labors (an average length of five hours with an upper limit of 14 hours) Active Labor (Active Phase) The active phase begins at 4 cm cervical dilation and ends when the cervix is dilated 8 cm. Contractions typically occur every two to five minutes and last 45 to 60 seconds and are of moderate to strong intensity. Progressive cervical dilation and fetal descent usually occur at this stage. For Primiparas, dilation should occur at approximately 1.2cm/hr. Multiparas progress at a slightly faster rate of 1.5cm/hr. These designations are only approximations and may vary a great deal if the woman receives medication, anesthesia, or other medical intervention during labor. Fetal descent is often slow in the first stage of labor, regardless of parity. Occasionally, the fetus does not descend during active labor. Transition (Transition Phase) Transition is the most difficult part of labor. This phase of the first stage of labor starts when the cervix is dilated 8 cm and ends with full cervical dilation. The contractions are strong of intensity, occur every two to three minutes, and are 60 to 90 seconds in duration. Frequently the woman experiences a strong urge to push as the fetus descends. It is important for the woman to resist the urge to push until the cervix is dilated completely as pushing against a partially dilated cervix can cause swelling, which slows labor, or the cervix can develop lacerations, leading to hemorrhage.

Bony Pelvis

The flared upper portion of the bony pelvis is the false pelvis. The false pelvis is not part of the bony passageway. The portion of the pelvis below the linea terminalis is the true pelvis. The true pelvis is the bony passageway through which the fetus must pass through during delivery. Important landmarks of the true pelvis include the inlet (entrance to the true pelvis), midpelvis, and outlet (exit point).

Powers

The primary force of labor comes from involuntary muscular contractions of the uterus. These labor contractions cause effacement and dilation of the cervix during the first stage of labor. Secondary powers are voluntary muscle contractions of the maternal abdomen during the second stage of labor that help expel the fetus. Each involuntary uterine contraction is composed of three phases: increment, acme, and decrement, followed by a relaxation period. The increment or building up of the contraction is the longest phase. During the increment, the contraction gains strength until is reaches the acme, or peak, of the contraction. The decrement is the letting-up phase, as the contraction relaxes gradually to baseline. Document contractions using three descriptors: frequency, duration, and intensity. Frequency refers to how often the contractions are occurring and is measured by counting the time interval from the beginning of one contraction to the beginning of the following contraction. Duration is the interval from the beginning of a contraction to its end. Intensity refers to the strength of the contraction. Estimate intensity by palpating the fundus at the peak of the contraction and record it as mild, moderate or strong. Intensity can be measured directly with an intrauterine pressure transducer. Each contraction constricts the blood vessels that supply the placenta, thereby decreasing the amount of oxygen that flows to the fetus. The relaxation period allows the vessels to fill with oxygen-rich blood to supply the uterus and placenta. Relaxation is also necessary so that maternal muscles do not become overly fatigued and to allow the laboring woman momentary relief from the pain of labor.

Second Stage: Birth

The second stage begins when the cervix is dilated fully to 10 cm and ends with the birth of the infant. Contractions usually continue at a frequency of two to three minutes, last 60 to 90 seconds, and are of strong intensity. The average length of the second stage is one hour for primiparas and 20 minutes for multiparas, although it is normal for a primipara to be in this stage for two hours or longer. During the second stage the woman is encouraged to use her abdominal muscles to bear down during contractions while the fetus continues to descend and rotate to the anterior position. Fetal descent is usually slow and steady for the primipara, from the active phase of the first stage through the second stage. Frequently the fetus of a multipara may not descend significantly during the active labor but may rapidly descend during the second stage. When the fetus is at a station of +4 he or she proceeds to move through the cardinal movements of extension and external rotation, followed by delivery of the shoulders and expulsion of the rest of the body.

Fetal Skull

The skull is the most important fetal structure in relation to labor and birth because it is the largest and least compressible structure. The diameter of the fetal skull must be small enough to allow the head to travel through the bony pelvis. Fortunately the fetal skull is not entirely rigid. The cartilage between the bones allows for the bones to overlap during labor, a process called molding which elongates the fetal skull, thereby reducing the diameter of the head. The newborn of a primipara often has significant molding.

Theories regarding the onset of labor

The three main theories regarding the onset of labor are the progesterone withdrawal theory, the oxytocin theory, and the prostaglandin theory.

Cardinal movements

The turns and movements made during the journey are referred to as the mechanisms of delivery or Cardinal movements. These include engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. While they are discussed separately, it is important to remember that these mechanisms may overlap or occur simultaneously. Engagement - Initial descent of the fetal head may result in engagement when the presenting part descends to the level of the ischial spines. Engagement can occur as early as two weeks before labor or not until after the onset of labor. Engagement is more likely to occur earlier in the primigravida and later in the multigravida. Descent - Descent may begin before labor when the fetus "drops." Descent is measured by station, which is the relationship of the fetal-presenting part to the maternal ischial spines. Descent continues throughout labor to varying degrees. Flexion - As the head descends during labor, the fetus encounters resistance from the soft tissues and muscles of the pelvic floor. This resistance normally coaxes the fetus to assume the attitude of flexion. Flexion is the attitude that presents the smallest diameters of the fetal head to the dimensions of the pelvis. Internal Rotation - Frequently, in early labor, the fetal head presents to the pelvis in a transverse position because the inlet of the pelvis is widest from side to side. During active labor, the fetal head typically rotates 45 degrees from a transverse position to an anterior position so that the head can accommodate the pelvic outlet, which is wider from the front to back. This movement is called internal rotation. If the fetus does not rotate, the widest diameters of the fetal head present to the outlet of the pelvis, resulting in a less than optimal fit between the head and the bony passageway. This can prolong labor. Extension - Typically, the fetal head is well flexed with the chin on the chest as the fetus travels through the birth canal. When the fetus reaches the pubic arch, it must extend under the symphysis pubis. External Rotation - As the head is born, external rotation lines the head up with the shoulders. Expulsion - Expulsion (birth) occurs after deliver of the anterior and posterior shoulders.

Maternal Psychological Adaptation

The woman's response to labor changes as it progresses. During early labor, the woman is often excited and talkative, although anxiety and apprehension are common responses. As labor becomes active the woman becomes more introverted and focuses her energies on coping with the stress of contractions. Women who are unprepared psychologically for labor lose control easily during the active phase and may resort to crying, screaming, or thrashing about during contractions. This response can impede the labor process by causing muscular tension. Tense muscles work against cervical dilation and fetal descent. Transition is the most intense phase of the first stage of labor and many women, even ones who have had natural childbirth classes, have a difficult time maintaining positive coping strategies during this phase of labor. Many women describe feeling out of control and need support, encouragement, and positive reinforcement. Once pushing efforts begin the woman usually feels more in control and is better able to cope. Maternal response to the actual birth vary wildly. While many mothers are excited and eager to hold the baby, others are exhausted and may doze intermittently. Most new mothers are anxious about the baby's health. When the woman holds the baby for the first time it is normal for her to use fingertip touching and for her to explore the infant and count his or her finger and toes.

Pelvic Shape

There are four basic pelvic shapes: gynecoid, anthropoid, android, and platypelloid. Most women have various combinations of these. The Gynecoid pelvis is the most favorable for a vaginal birth. The rounded shape of the gynecoid inlet allows the fetus room to pass through the dimensions of the bony passageway. This pelvis is considered the typical female pelvis although only about 50% of all women have this type of pelvis. The Anthropoid Pelvis is elongated in its dimensions. the anterior-posterior diameter is roomy, but the transverse diameter is narrow compared with that of the gynecoid pelvis. However, a vaginal birth can often be accomplished in approximately one third of women who have variations of this type of pelvis. The Android Pelvis is the typical male pelvis and resembles a heart in its shape. Approximately one third of white women and 16% of non white women have an android pelvis. Large babies often become stuck in the birth canal and must be delivered by cesarean, whereas a smaller baby may be able to navigate the narrow diameters. The least common type is the platypelloid pelvis. This pelvis is flat in its dimensions with a very narrow anterior-posterior diameter and a wide transverse diameter. This shape makes it extremely difficult for the fetus to pass through. Therefore women with this pelvis must usually deliver the fetus by cesarean section.

Maternal Physiologic Adaptation

There is increased demand for oxygen during the first stage of labor, attributable in part to the energy used for uterine contractions. to meet the demand there is a moderate increase in cardiac output throughout the first stage of labor. During the second stage, cardiac output may be increased as much as 40 to 50% above pre-labor levels. Immediately after birth, it may peach at 80% above the pre-labor level. The pulse is often on the high end of normal during active labor. Dehydration and/or maternal exhaustion accentuate these normal increases in heart rate. Blood pressure however does not change appreciably during normal labor although the stress of contractions may cause a 15mm hg increase in the systolic pressure. The increased demand for oxygen and the pain of the uterine contractions cause the respiratory rate to increase which puts the laboring woman at risk for hyperventilation. Mouth breathing and dehydration contribute to dry lips and mouth. Labor prolongs the normal gastric emptying time. This change often leads to nausea and vomiting during active labor and increases the woman's risk for aspiration, particularly if general anesthesia is required. Traditionally the laboring woman receives IV fluids while solid food and fluids are withheld, but research shows that the risk for aspiration remains high even if the woman maintains an NPO status because gastric secretions become more acidic during periods of fasting. Current recommendations are to allow the laboring woman to have clear liquids, unless there is a high likelihood that she will deliver by cesarean. Pressure on the urethra from the presenting part may cause overfilling of the bladder, a decreased sensation to void, and edema. A full bladder is uncontrollable and slows the progress of labor. As the bladder fills it rises upward in the pelvic cavity, which puts pressure on the lower uterine segment and prevents the head from descending. Sometimes a straight cath becomes necessary to empty the bladder. Labor affects some lab values. The stress of vigorous labor may cause an increase in white blood cell count to as high as 30,000 cells/microliter (mcL). This increase is the body's normal response to inflammation, pain and stress. Frequently the urine specific gravity is high, indicating concentrated urine, and there may be a trace amount of urinary protein because of increased metabolic activity. Gross proteinuria is never normal during labor and is a sign of a developing complication.