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10 Intrapartum Care and Fetal Surveillance Carolina Ghia, Luciana Prozzillo, and Gustavo F. Leguizamón
In the last 50 years different techniques have been developed to assess fetal health during labor. From intermittent auscultation to the most recent invasive techniques, the objective of these methods is to detect fetal stress early, so that complications, such as intrapartum fetal hypoxia leading to cognitive impairment, cerebral palsy, or even fetal death, can be prevented. Persistent intrapartum hypoxia, which complicates about 1 % of all labors, can lead to severe acidemia, which in turn may compromise those vital tissues requiring strict oxygen levels, such as in the renal, cardiovascular, and central nervous systems. The latter is the most vulnerable to oxygen deprivation and is, therefore, frequently involved in long-term sequelae. Thus, an ideal method of intrapartum fetal surveillance should be able to differentiate between transient hypoxia without metabolic acidosis and pathologic hypoxia leading to acidosis and tissue damage. This is of utmost importance, since it allows accurate intervention and prevention of long-term sequelae without increasing unnecessary cesarean sections. In other words, it requires a method with a high degree of sensitivity and a low false-positive rate. Since alterations in maternal blood pressure, heart rate, and uterine contractions have direct effects on fetal oxygenation, maternal vital signs should be monitored during labor, especially in the event of a non-reassuring fetal pattern. Fetal heart rate and its variations is a good parameter of fetal response to labor events. In particular, knowledge of normal and abnormal patterns will allow both detection of fetal distress and accurate intervention. Other methods of measuring metabolic status, such as fetal blood sampling, pulse oximetry, and lactate measurement, have been developed in order to complement fetal assessment. These methods are discussed in detail in this chapter.
Definitions
Acceleration: This describes a short-term rise in fetal heart rate of greater than 15 beats per minute (bpm) that lasts for more than 15 seconds. Acidemia: This condition arises from increased hydrogen content in the blood. Acidosis: This term describes a state of increased hydrogen content in the tissues. Respiratory acidosis: The accumulation of CO2 leads to respiratory acidosis. When the umbilical cord is compressed, CO2 rapidly accumulates in the fetal blood. Metabolic acidosis: During the peak of uterine contraction, intramyometrial pressure exceeds uterine arterial pressure and therefore, the blood flow decreases, leaving the fetus in a transient state of hypoperfusion. In the event of basal inadequate oxygen delivery to the fetus, this transitory lack of perfusion leads to fetal hypoxia, which can result in metabolic acidosis. Asphyxia: This is a state of hypoxia with metabolic acidosis. Deceleration: This describes a fall in the fetal heart rate of greater than 15 bpm that lasts for more than 15 seconds (but less than 10 minutes). Hypoxemia: This condition occurs following decreased oxygen concentration in the blood. Hypoxia: This term describes decreased oxygen concentration in the tissues.
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Part II Obstetrics
Fetal Heart Rate: Normal and Pathologic Patterns
The normal fetal heart rate at term varies between 110 and 160 bpm. This is measured by a cardiotachometer during intrapartum fetal monitoring and is defined as the baseline heart rate, which is much higher in the second trimester and declines thereafter with increasing gestational age. This decline in baseline heart rate is a good indicator of development of the vagal tone. A heart rate above 160 bpm that persists for more than 10 minutes (a shorter period could represent a transient acceleration) is referred to as tachycardia. Among the most frequent causes of tachycardia are maternal fever (as seen in chorioamnionitis), the use of drugs that elevate heart rate (e. g., ritodrine), fetal anemia, and fetal arrhythmias. However, if tachycardia is persistent, it can also indicate fetal hypoxia. A heart rate of less than 110 bpm that persists for more than 10 minutes (as distinct from transient deceleration) is known as bradycardia. Some fetuses have normal baselines of 100–105 bpm. However, in most cases, it indicates some metabolic alteration (e. g., maternal hypothermia or hypoglycemia), use of drugs that diminish heart rate (e. g., magnesium sulfate), or cardiac abnormalities (e. g., heart block, umbilical cord occlusion).
Decreased variability is defined as less than 5 bpm for longer than 80 minutes (Fig. 10.2). It may reflect different physiological conditions, including fetal sleep and prematurity, or may be secondary to drugs such as narcotics, barbiturates, tranquilizers, phenotiazines, and general anesthetics. Among the pathologic causes of decreased heart rate variability are maternal hypoglycemia, reduced fetal oxygenation and acidosis, major anomalies of the fetal central nervous system, chorioamnionitis, and fetal heart block.
Transient Accelerations Heart rate accelerations are usually a response to fetal movement or external stimulations, such as uterine contractions (Fig. 10.3). Their spontaneous presence indicates absence of hypoxia, especially in the context of normal baseline and variability. The presence of provoked accelerations, even in a context of non-reassuring fetal heart rate, rules out a pH lower than 7.20 on scalp sampling. The absence of accelerations should be interpreted in the context of other variables. In general, if the fetal heart rate pattern is non-reassuring with no accelerations, approximately half of such fetuses will be acidotic. On the other hand, the lack of accelerations in an otherwise reassuring pattern is generally not associated with an increased fetal risk of hypoxia.
Variability Transient Decelerations The difference in heart rate from beat to beat, which is registered by a device known as a cardiotachometer as a trace moving over and under the baseline, is known as variability (Fig. 10.1). Normal variability ranges from 5 bpm to 25 bpm, and is an indicator of a well-functioning fetal brain. However, heart rate variability increases with gestational age, reaching a stable pattern at approximately 28 weeks of gestation. Variations between fetuses are also observed.
Decelerations are classified in three groups, according to their location regarding uterine contractions: • Early decelerations. These coincide with uterine contractions and appear as vagal reactions in response to fetal head compression during the final stages of labor and they are not associated with fetal hypoxia, however. The drop in fetal heart rate appears as a
Fig. 10.1 Fetal heart rate variability that changes with gestational age is an indicator of a well-functioning fetal brain.
10 Intrapartum Care and Fetal Surveillance
Fig. 10.2 Decreases in fetal heart rate variability (as indicated by the changes in peak size) may reect aberrant physiologic conditions that may harm the fetus.
Fig. 10.3 The presence of accelerations, which can be provoked by uterine contractions, can rule out problems such as hypoxia and acidosis.
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V-shaped pattern coinciding with the uterine contraction, and does not persist beyond it. They create a “mirror” image of the contraction in the monitor trace, with their nadir in coincidence with the peak of the contraction. • Variable decelerations. These are the most common type of deceleration during labor. They are called “variable” because of the lack of a particular relation with contractions, and the absence of a consistent pattern (Fig. 10.4). These decelerations usually are not associated with fetal hypoxia. They are caused by fetal heart rate changes in response to blood pressure alterations, which are frequently due to cord compression. When the cord vein is compressed, CO2 accumulates in fetal blood; this can produce respiratory acidosis. If compression continues, oxygen delivery becomes insufficient; producing metabolic acidosis, turning the situation into mixed acidosis.
Variable decelerations can be further classified according to their severity: • Mild decelerations. These have duration of less than 30 seconds regardless of the depth, or heart rate not below 80 bpm regardless of duration. • Moderate decelerations. These fall below 80 bpm. • Severe decelerations. These are decelerations that last for more than 60 seconds and fall to less than 70 bpm. • Late decelerations. These generally appear within 30 seconds of a contraction; their nadir is delayed with respect to the peak of the contraction, usually descend no more than 40 bpm from the baseline, and last a variable amount of time beyond the contraction (Fig. 10.5). Late decelerations reflect transient periods of fetal hypoxia due to a diminished uterine– placental blood flow during a contraction. The severity of hypoxia cannot be predicted from the depth of the deceleration. The persistence in time of late
Fig. 10.4 Variable decelerations are usually not associated with fetal hypoxia but are frequently caused by cord compression.
10 Intrapartum Care and Fetal Surveillance
Fig. 10.4 (continued)
Fig. 10.5 Late decelerations reflect transient periods of fetal hypoxia during contractions.
decelerations gives a more reliable reason to suspect hypoxia and fetal metabolic acidosis. A fetus whose placenta suffers from any pathologic condition is more likely to develop late decelerations in response to decreased oxygen exchange. This condition usually includes maternal hypertension or pre-eclampsia, maternal diabetes, or collagen vascular diseases.
Sinusoidal Pattern A sinusoidal pattern is strongly associated with severe fetal anemia and hypoxia. Its characteristics include: 1. Stable baseline fetal heart rate of 120–160 bpm with regular sine-wave–like oscillations (Fig. 10.6) 2. Amplitude of 5 to 15 bpm
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100
100
80
80
80
60
60
60
40
40
40
20
20
20
0
0
0
3. Frequency of 2 to 5 cycles/min 4. Fixed or absent short-term variability 5. Oscillation of sine wave above and below the baseline 6. Absence of accelerations
Other Methods for Intrapartum Fetal Surveillance Intermittent Auscultation Intermittent auscultation was originally performed with the Pinard stethoscope (Fig. 10.7). In the 1950s it was replaced by Doppler sonographic technology, which has the advantage of easier localization of fetal heart tones as well as giving the patient the ability to hear her baby’s heart beat, giving her more confidence in the labor process. Fetal auscultation should be performed every 15 minutes and 5 minutes, respectively, in the first and second stage of labor. It then should be performed throughout labor as well as for 60 seconds following each contraction. In low-risk patients, the frequency should be at least every 30 minutes in the first stage and every 15 minutes in the second stage. Even with correct techniques, there are disadvantages to this method, including inaccurate information about late decelerations and the inability of registering baseline variability. Although comparisons between continuous fetal heart rate monitoring (see below) and intermittent auscultation during labor in low-risk patients has failed to demonstrate benefits in neonatal outcomes, the number of personnel needed for the latter technique (one-to-one care is required) make it difficult to perform.
Fig. 10.6 A sinusoidal pattern, which is characterized by regular sine-wave–like oscillations with little variability and an absence of accelerations, is a potential indicator of fetal hypoxia and anemia.
Continuous Electronic Fetal Heart Rate Monitoring Although reactivity is often absent in intrapartum heart rate tracings, a healthy fetus usually tolerates labor well, showing normal variability and without severe persistent decelerations. Continuous monitoring of fetal heart rate has several advantages over intermittent auscultation, including: • requiring fewer personnel to administer • the ability to obtain a printed strip, which allows comparisons of fetal responses during the progressive stages of labor • being more accurate in diagnosing late decelerations • producing reduced variability, and • allowing for the simultaneous measurement of uterine contractions This method has an excellent sensitivity in detecting fetal hypoxia during labor, but very poor specificity (Evidence Box 10.1). It employs a Doppler heart-rate detector that translates heart beats into dots in a paper strip which, joined together, form the line moving above and below the horizontal baseline, representing variability. A transducer is placed on the mother’s abdomen upon the pro-
Fig. 10.7 An aluminum Pinard fetal stethoscope.
10 Intrapartum Care and Fetal Surveillance
jection of the fetal shoulder. A tocodynamometer is also placed in the mother’s abdomen, in the projection of the uterine fundus, to obtain simultaneous reading of uterine contractions. Approximately one-half of fetuses that present with a non-reassuring pattern during labor (e. g., reduced variability, persistent decelerations progressing in severity, tachycardia, or bradycardia) are born with normal Apgar scores. If the patient’s membranes are ruptured and there is difficulty in obtaining good recordings with external monitoring, an internal electrode can be applied to the fetal scalp for a more accurate tracing.
Fetal Pulse Oximetry Fetal pulse oximetry is a tool that measures fetal arterial O2 saturation using a sensor attached to the fetus’ temple or cheek. Normal fetal O2 saturation during labor is 40–70 %. Values below 30 % are strongly associated with pH under 7.20. The American College of Obstetricians and Gynecologists states that further studies confirming safety and efficacy are required before recommendation of this technology. To use it, the membranes must be ruptured and the cervix ought to be dilated 2 cm or more.
Meconium
Fetal Metabolic Status Assessment
In order to improve the specificity of continuous monitoring for fetal hypoxia/acidemia and to prevent unnecessary operative interventions, invasive procedures have been developed to further evaluate non-reassuring patterns in the electronic heart-rate monitoring. One such method is fetal pulse oximetry, whereby a specially adapted device is placed in contact with the fetus’ cheek to provide information about fetal oxygenation during labor. Another method involves sampling fetal blood in order to measure pH, base deficit, and lactate as direct parameters of the fetal metabolic status. This involves obtaining samples by puncturing the fetal scalp. However, this method can only be used if the membranes are ruptured and the woman’s a cervix is dilated at least 4–5 cm).
Fetal Scalp pH This is the most accurate technique to diagnose fetal acidosis. It consists of taking a blood sample from the fetal scalp using a lancet and a capillary collection tube. During labor, normal pH is above 7.24. A pH value between 7.20 and 7.24 indicates pre-acidemia, and a pH lower than 7.20 indicates acidosis. Complementing electronic fetal monitoring with fetal scalp pH measurement should reduce cesarean rates for non-reassuring fetal status. However, the technique is rarely used. Measurement of base excess of umbilical artery is a great tool for differentiating respiratory from metabolic acidosis. Base excess below −12 mmol/L has a high correlation with increased risk of neonatal neurologic injury.
Meconium is the normal content of the fetal gut. When the fetus is suffering from hypoxia, because of gut vasoconstriction, there can be passage of meconium to the amniotic fluid. Hypoxia also works as an important stimulus for fetal gasping, which can result in fetal aspiration of meconium. Thick meconium is frequently associated with oligohydramnios, which in turn is a sign of placental dysfunction. Nevertheless, with normal fetal heart rate, the presence of meconium does not always reflect fetal hypoxia.
Amnioinfusion In variable decelerations caused by oligohydramnios, this technique can improve Apgar score and pH values and can also reduce the number of cesarean sections for nonreassuring fetal status. Amnioinfusion might reduce the cord compression that leads to hypoxia. It is also used in the presence of meconium to dilute it.
Interventions for Altered Heart Rate Patterns Clinical Management The following steps should be taken when an altered heart rate pattern is detected via continuous monitoring: • Assess the mother’s vital signs and uterine tone. It is possible that fever, hypotension, hypertonic uterus, or tachysystolia may be causing fetal distress.
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• Place the mother in the left lateral position. This action relieves uterine compression of the vena cava, allowing better blood flow. • Increase oxygen supply. Administer oxygen to the mother via a nasal cannula or a mask to improve the mother’s Po2 and therefore placental O2 exchange. • Increase intravenous hydration. This helps to maximize uterine flow and perfusion and to correct a possible hypotension as a cause of the abnormal pattern. • Discontinue oxytocin infusion (if being administered). This will improve placental perfusion as it decreases uterine contractions. • Initiate acoustic or scalp stimulation. Fetuses who respond with increased heart rate upon stimulation have better outcomes than those who don’t. Usually, fetal response to either acoustic or scalp stimulation reflects a lack of acidosis.
baseline variability and late and prolonged decelerations. Fetal heart rate patterns with absent baseline variability were the most specific, but identified only 17 % of the asphyxia group. The sensitivity of this test increased to 93 % with the addition of less specific patterns. The estimated positive predictive value ranged from 18.1 % to 2.6 %, and the negative predictive value ranged from 98.3 % to 99.5 %. The investigators concluded that a narrow 1-hour window of fetal heart rate patterns, including minimal baseline variability and late or prolonged decelerations, can predict fetal asphyxial exposure before decompensation and newborn morbidity. Thus, with careful interpretation, predictive fetal heart rate patterns can be a useful screening test for fetal asphyxia. However, supplementary tests are required to confirm the diagnosis and to identify the large number of false-positive patterns to avoid unnecessary intervention. Low JA, Victory R, Derrick EJ. Predictive value of electronic fetal monitoring for intrapartum fetal asphyxia with metabolic acidosis. Obstet Gynecol 1999 Feb;93(2):285-91.
Operative Management Further Reading When a fetus is considered to be “at risk” due to a persistent non-reassuring pattern in continuous fetal monitoring, and back-up studies cannot offer reassurance, the physician must proceed with rapid delivery. The choice between instrumental vaginal delivery and cesarean section will depend on the stage of labor, cervical dilatation, vertex station, and the estimated time for performing each procedure. Therefore, each case must be analyzed individually in order to achieve delivery in the least amount of time and without exposing the mother and fetus to unnecessary procedures. Key Points • The objective of the intrapartum fetal testing is to determine whether the fetus presents hypoxia and/or metabolic acidosis. • If hypoxia is detected, attempts to reverse it by interventions such as hydration, discontinuation of oxytocin, oxygen supply, or fetal stimulation must be performed. • If persistent non-reassuring results are observed in spite of such interventions, expedited delivery must be initiated.
Evidence Box 10.1 Careful interpretation of specific FHR patterns can be a useful screening test for fetal asphyxia. However, supplementary tests are required to identify the large number of false-positive patterns to avoid unnecessary intervention. Low et al. analyzed selected patterns of important fetal heart rate variables, during the last hour before delivery, for their predictive value for fetal asphyxia among a group of 71 term infants with umbilical artery base deficit >16 mmol/L, and a control group of 71 term infants with umbilical artery base deficit <8 mmol/L. The fetal heart rate variables associated with fetal asphyxia included absent and minimal
American College of Obstetricians and Gynecologists. Fetal Distress and Birth Asphyxia. ACOG Committee Opinion 1994, No 137, Washington, DC American College of Obstetricians and Gynecologists. Fetal Heart Rate Monitoring, Interpretation and Management. ACOG Technical Bulletin 1995, No. 207, Washington, DC Dildy G. Intrapartum assessment of the fetus: historical and evidence-based practice. Obstet Gynecol Clin 2005, Vol. 32, Issue 2. National Institute of Child Health and Human Development Research Planning Workshop. Electronic fetal heart rate monitoring: research guidelines for interpretation. Am J Obstet Gynecol 1997;177(6):1385–1390 Gabbe SG, Niebyl JR, Simpson JL. Obstetrics—Normal and Problem Pregnancies. 5th ed. New York: Churchill Livingstone / Elsevier; 1997 Graham E. Intrapartum electronic fetal heart rate monitoring and the prevention of perinatal brain injury. ACOG 2006, Vol. 108, No.3, Part 1 Jibodu OA, Arulkumaran S. Intrapartum fetal surveillance. Curr Opin Obstet Gynecol 2000;12(2):123–127 Smith JF Jr, Onstad JH. Assessment of the fetus: intermittent auscultation, electronic fetal heart rate tracing, and fetal pulse oximetry. Obstet Gynecol Clin North Am 2005;32(2):245–254
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11 Labor and Delivery
This chapter reviews the determinants of human parturition, or labor. Labor is a physiologic process consisting in organized uterine contractions of adequate intensity, frequency, and duration to aďŹ&#x20AC;ect complete cervical dilatation and expulsion of the fetus, placenta, and fetal membranes through the birth canal. Labor progresses from a state of uterine quiescence (latent phase) to a phase characterized by uterine contractions and cervical dilatation (active phase). Maternal structures (e.g., pelvis) and functions (e.g., uterine contractions) as well as fetal structures (e.g., presenting parts) and functions (e.g., fetal cardinal movements) are of utmost importance in the progression of labor.
Uterine contractility
Vanina S. Fishkel and Gustavo F. Leguizamòn
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Labor Physiology
The physiology of term labor initiation is not fully elucidated, but during the past several decades signiďŹ cant information has been added to our understanding of this process. Uterine activity can be classiďŹ ed as having four distinct phases (Fig 11.1): â&#x20AC;˘ Phase 0 (quiescence). This Phase is characterized by uterine quiescence and the leading hormone is progesterone. â&#x20AC;˘ Phase 1 (activation). In this Phase, receptors for oxytocin and prostaglandins are actively synthesized as well as an increased number of gap junctions, leading to a progressive increase in uterine sensitivity to different uterotonics. Estrogens play a pivotal role in this phase. â&#x20AC;˘ Phase 2 (stimulation). Once the uterus has reached its potential to respond, oxytocin and prostaglandins stimulate contractions actively. â&#x20AC;˘ Phase 3 (involution). After delivery, oxytocin leads to uterine contraction and bleeding decreases signiďŹ cantly.
Fig. 11.1 Uterine activity in pregnancy. Adapted from Challis JRG, Gibb W: Control of Parturition. Prenatal and Neonatal Medicine 1996;1:283.
Mechanics of Labor
Adequate interaction between the fetusâ&#x20AC;&#x2122; features and maternal pelvis allows vaginal delivery. Thus, maternal contractions to propel the fetus through the birth canal and the ability of the fetus to pass through the motherâ&#x20AC;&#x2122;s pelvic bones are crucial to successful labor and birth.
Contractions Uterine contractions are characterized by the following measurable parameters: Amplitude or intensity: The ability of the external tocodynamometer or manual palpation to determine contraction intensity is limited and of no clinical value. Intensity can be measured more precisely by an intrauterine pressure catheter. This device is placed transcervically inside
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the uterine cavity after membrane rupture and above the fetal presenting part. The Montevideo Unit attempts to measure objectively the intensity of the contraction. It is calculated by the average strength of contractions in millimeters of mercury multiplied by the number of contractions in 10 minutes. During the active phase of labor, 200–250 Montevideo Units are considered normal. Since an internal catheter is not routinely used in clinical practice, the ability to measure intensity of uterine contractions is limited. Frequency: Laboring patients in the active phase usually contract 3–5 times in 10 minutes. The presence of more than 5 contractions in 10 minutes for a period of 20 minutes is abnormal and is defined as tachysystole. When an alteration in the fetal heart rate accompanies tachysystole it is called hyperstimulation. Duration: The sensitivity to detect the uterine contractions varies with different methods. The highest sensitivity is observed with internal catheters followed by palpation and, finally, patient perception. External tocodynamometer determinations are biased by the sensitivity of the device as well as maternal body habit.
The Pelvis Fig. 11.2 A Martin pelvimeter.
Since the progression of labor and fetal descent are determined in part by the relationship of the fetal presenting part and the bony pelvis, the obstetrician must become familiar with the evaluation of the pelvic dimensions, which is traditionally determined by a pelvimeter (Fig. 11.2). Overall, four different shapes of female bony pelvis have been described. Two of them with favorable characteristics for vaginal delivery (gynecoid, anthropoid), and two (android, platypelloid) more frequently associated with cephalopelvic disproportion (CPD). The bony pelvis (Fig. 11.3) is composed of the sacrum, ilium, ischium, and pubis. The pelvic brim separates the false (greater) pelvis from the true (lesser) pelvis. The true pelvis is further divided into three sections: 1) the pelvic inlet, 2) midpelvis, and 3) pelvic outlet.
Pelvic Inlet The following are the measurable parts of the pelvic inlet. Diagonal conjugate: This is the distance from the sacral promontory to the inferior margin of the symphysis pubis. This measure can be obtained by vaginal examination.
Sacroiliac joint
Sacrum
Sacral promontory
Anterior superior iliac spine
Ilium
Acetabulum
Pubis
Obturator foramen Subpubic angle
Coxa
Ischium Symphysis pubis
Fig. 11.3 Anatomyof the bony pelvis, anterior view.
11 Labor and Delivery
True or obstetric conjugate: This is the distance from the sacral promontory to the superior margin of the symphysis pubis. It is the shortest diameter of the pelvic inlet. Values below 10 cm are frequently associated with CPD. Although this measure cannot be obtained by vaginal examination, it can be calculated by subtracting 2 cm from the diagonal conjugate.
Midpelvis The interspinous diameter: This is the distance between the ischial spines. It is the shortest diameter and measures below 10 cm are associated with CPD.
Position: In cephalic presentation the occiput is the anatomical reference, and its localization in relation to the maternal axis determines the fetal position. For example, if the occiput is localized anterior straight to the pubic arch, it is occiput anterior (OA), and if it is toward the mother’s right, then it is right occiput anterior (ROA). Figure 11.4 depicts the possible fetal positions in vertex presentation. Station: This refers to the relation of the lowest bony fetal part to the ischial spines. It is a measure of descent of the fetus in labor and is classified according to the distance in centimeters from the plane of the ischial spines (Fig. 11.5).
Pelvic Outlet Clinical examination allows evaluation of the pubic angle, prominence of the coccyx, and intertuberous diameter of the pelvic outlet.
The Fetus
Fetal characteristics are of utmost importance in the progression of labor. Important parameters include fetal size, lie, presentation, attitude, position, and station. Fetal size: The impact of this measure in the progression of labor is relative to the maternal pelvis. However, macrosomic infants (>4500 g) need to be delivered by cesarean section significantly more often than normal birth weight babies.
Cardinal Movements of Labor
During labor, the fetus dynamically interacts with the rigid maternal bony pelvis to offer the best possible diameter to the pelvic path. Seven main movements are identified in the fetus (Fig. 11.6). Engagement: This occurs when the widest diameter of the presenting part (biparietal diameter in cephalic or bitrocantheric diameter in breech presentation) reaches a plane below the pelvic inlet. In cephalic presentation as seen at vaginal examination, the presenting part is at 0 station and the fetus is engaged. Descent: The descent of the presenting part is through the pelvic birth canal.
Lie: This term refers to the relation between the fetal and maternal longitudinal axis. It can be longitudinal, transverse, or oblique. Longitudinal lie is required to achieve a successful vaginal delivery.
Flexion: To improve the ability to pass through the birth canal, flexion of the head (the chin lies against the chest) occurs. This allows presentation of the smallest diameter of the fetal head, the suboccipitobregmatic.
Presentation: This refers to the fetal part being offered to the pelvic inlet. It can be cephalic (vertex), breech, or compound (when multiple fetal parts are offered to the pelvic inlet). The presentation is further classified according to the main bony presenting part. For example, in a cephalic presentation, different degrees of fetal cervical flexion can offer different anatomical landmarks such as occiput (vertex), the chin (mentum), and the brow.
Internal rotation: Most frequently, the presenting head enters the pelvis in transverse position. By internal rotation the head turns to OA position (towards the pubis), offering the best diameter to the pelvic canal.
Attitude: This consists in the position of the head with regard to the fetal spine. The optimal attitude is with the head flexed and the chin against the chest, presenting the smallest possible head diameter to the pelvic inlet, or the suboccipitobregmatic diameter.
External rotation: Once the fetal head is delivered it rotates back in line with the anatomical position of the fetal body.
Extension: Once the fetal head reaches the introitus, it extends leaving the pubis symphysis at the base of the occiput. This facilitates the delivery of the fetal head.
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Fig. 11.4 Fetal presentation and position. LOA, left occiput anterior; LOT, left occiput transverse, LOP, left occiput posterior; ROA, right occiput anterior; ROT, right occiput transverse; ROP, right occiput posterior.
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Uterus
LOA
LOT
LOP
ROA
ROT
ROP
Large 41-week fetus in vertex position engaged at -2 station
Placenta
-3 -1 +1 +3
Fig. 11.5 Fetal descent stations (birth presentation).
10 cm dilatation of the cervix
-2 0 +2
11 Labor and Delivery
Fig. 11.6 Cardinal movements of labor.
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Expulsion: This describes the delivery of the rest of the fetal body. The delivery of the anterior shoulder follows the same pattern of rotation as the delivery of the head.
Progress of Labor Stages The three stages of labor are: • First stage. Extending from the onset of labor to full cervical dilatation • Second stage. Extending from full cervical dilatation until fetal delivery • Third stage. Extending from the delivery of the baby until the placenta is delivered
Phases There are two phases of labor: latent and active. • Latent phase. Extending from initiation of labor until active labor is achieved. The diagnosis of labor initiation is subjective, and usually refers to the presence of regular contractions. • Active phase. Labor usually is considered active when there is 80 % effacement and greater than 4 cm of cervical dilatation is achieved.
1.2 cm and 1.5 cm per hour for nulliparous and multiparous women, respectively. The use of epidural analgesia appears to prolong these time periods. Table 11.1 depicts mean and 95th percentile for duration of first and second stage of labor. During labor, risk factors for a prolonged second stage, such as macrosomia or maternal diabetes, must be identified. Once the fetal head is crowning, the physician must control the delivery of the head. It is critical to protect the perineal region with the other hand to diminish the risk for tears. Once the head is delivered, external rotation is permitted or gently assisted. At this point, look for the nuchal umbilical cord and, if present, reduce it. If it is tight and reduction is not feasible, perform clamping and section at this point, before delivery of the rest of fetal body. Currently, there is not robust evidence to support routine oropharynx aspiration. The anterior shoulder is then delivered by gentle downward traction. Subsequently, the delivery of the posterior shoulder is assisted by gentle upward traction. Again, protection of the maternal perineal region is important at this stage. The placenta and membranes are delivered passively. Manual intervention is only considered after 30 minutes of expectant management. After delivery, examine the placenta and membranes for integrity, and document the number of cord vessels.
Table 11.1 Duration of second stage of labor (mean and 95th percentile) Mean
95th percentile
Latent labor
7.3–8.6 h
17–21 h
First stage
7.7–13.3 h
16.6–19.4 h
First stage epidural
10.2 h
19 h
Second stage
53–57 min
122–147 min
8
Second stage epidural
79 min
185 min
6
Multiparas Latent labor
4.1–5.3 h
12–14 h
First stage
5.7–7.5 h
12.5–13.7 h
First stage epidural
7.4 h
14.9 h
Second stage
17–19 min
57–61 min
Second stage epidural
45 min
131 min
To objectively monitor the progress of labor and to identify patients that require further evaluation, it is practical to plot the progress of labor as a labor curve (Fig. 11.7). In general, the rate of dilation during the active phase is
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Accel. phase
4
Phase of max. slope Decel. phase Sec. stage Active phase
2
0
Latent phase 0
2
4
6
8 Time (hours)
Fig. 11.7 A typical labor graph.
10
12
Parameter Nulliparas
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11 Labor and Delivery
Midline incision
a
Mediolateral incision
Fig. 11.8 Options for an episiotomy incision.
b
Episiotomy Episiotomy is an incision in the perineal region performed when the fetal head crowns. The objective of this intervention is to reduce the risk of perineal trauma. It could be median (vertical medial midincision from the vagina toward the anal sphincter) or mediolateral (at a 45° angle from the vagina) (Fig. 11.8). Although it was previously believed that episiotomy could favor delivery and decrease perineal trauma, current studies have shown that midline episiotomy increases the risk of third and fourth degree tears. Therefore, episiotomy should not be used routinely (See Evidence Box 11.1) and must be reserved for special circumstances, such us the relief of shoulder dystocia.
Operative Vaginal Delivery
In selected cases operative delivery either by forceps or vacuum extraction, instrumentation is required.
Forceps Delivery Three general classes of forceps exist: • Classic forceps. These are designed for traction in vertex presentation, but are not designed for rotation of the fetal head. The most common forceps in this group are Tucker-McLane, Simpson, and Elliot. • Rotational forceps. This is characterized by the lack of pelvic curvature (to avoid pelvic damage on rotation) and sliding lock (to facilitate the application on asynclitic presentations). The most common forceps in this group is Kielland.
• Forceps to deliver the aftercoming head in breech presentation. This forceps has a cephalic curve consisting of a reverse pelvic curve. When its application is required, the trunk of the baby is held horizontally and the forceps is applied from below (Fig. 11.9). This maneuver is feasible because of the inverse pelvic curve. This forceps is called Piper.
Vacuum Extraction The vacuum extraction device consists of a stainless steel or a plastic cup attached to a handle grip and a tube that connects to a vacuum source. Fundamentals for application are the same for either vacuum extraction or forceps delivery and require: • baby to be in an engaged vertex presentation • cervix to be fully dilated • membranes to be ruptured • bladder to be drained • adequate assessment of fetal position in relation to the maternal pelvis • availability of maternal analgesia • acquisition of informed consent • operator to be trained in forceps delivery/vacuum extraction • willingness to abandon the procedure if unsuccessful Indications to consider operative vaginal delivery are also similar for both techniques and include a prolonged second stage. For, nulliparous women, indications for vaginal delivery include the lack of progression for 2 hours when no regional anesthesia is used, and for 3 hours if analgesia was applied. For multiparous women, indicators for vaginal delivery include lack of progression for 1 hour when no regional anesthesia is used, and for 2 hours if analgesia was applied.
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Section I Normal Obstetrics
Part II Obstetrics
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Evidence Box 11.1 Restrictive use of episiotomy leads to fewer complications than routine use. Carroli and Mignini reviewed the scientific literature to determine the effects of restrictive use versus routine use of mediolateral and midline episiotomy. In reviewing eight randomized, controlled trials that included more than 5 500 women, they found that compared with routine use, restrictive episiotomy resulted in less severe perineal trauma, less suturing, and fewer healing complications. There was no difference in severe vaginal/perineal trauma, dyspareunia, urinary incontinence, or several pain measures between the two groups. Restrictive episiotomy was, however, associated with more anterior perineal trauma. The authors concluded that restrictive episiotomy appears to have a number of benefits compared to policies based on routine episiotomy. Carroli G, Mignini L. Episiotomy for vaginal birth. Cochrane Database Syst Rev 2009 Jan 21;(1):CD000081.
Fig. 11.9 The Piper forceps is applied to the fetal head from below. This is the preferred method of delivering the head of a breech baby.
Key Points • Labor is a physiologic process consisting in the occurrence of organized uterine contractions of adequate intensity, frequency, and duration leading to complete cervical dilatation and expulsion of the fetus, placenta, and fetal membranes through the birth canal. • Physiology of labor initiation involves different phases characterized by quiescence, activation, stimulation, and involution. • Normal labor pattern consists in 3–5 contractions in 10 minutes. The presence of more than 5 contractions in 10 minutes for a period of 20 minutes is abnormal and is defined as tachysystole. • The cardinal movements of labor are engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. • Routine median episiotomy is associated with increased incidence of pelvic tears.
Further Reading American College of Obstetricians and Gynecologists: Dystocia and augmentation of labor. ACOG Practice Bulletin No. 49, December 2003 American College of Obstetricians and Gynecologists: Episiotomy. ACOG Practice Bulletin No. 71, April 2006 Reece EA, Hobbins JC, eds. Clinical Obstetrics—the Fetus and Mother. 3rd ed. Malden, Mass: Blackwell Synergy Publishing, 2007 Gabbe SG, Niebyl JR, Simpson JL. Obstetrics: Normal and Problem Pregnancies. New York: Elsevier / Churchill Livingstone; 2007