Labor and Delivery and Their Complications

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Chapter 181

Labor and Delivery and Their Complications

Shoma Desai and Sean O. Henderson

Perspective

Emergency department (ED) births are rare. In most cases, patients in labor are triaged directly to the obstetric suite for urgent management, maintaining a continuum of care with their primary providers. Because some births are precipitous and obstetric resources may not be immediately available, the emergency physician must possess the basic skills for intrapartum management of both normal and abnormal deliveries. In addition, a general knowledge of postpartum care is required in case of the occasional out-of-hospital delivery.1,2

Limitations of the Emergency Department

The ED is a suboptimal location for the management of a complicated delivery. The obstetric suite has experienced personnel and appropriate resources, including tocodynamometry, fetal scalp electrodes, intrauterine pressure monitors, vacuum extractors, and forceps. Also, the obstetrician usually has prenatal care information for each patient that helps optimize maternal and fetal outcomes. Such information includes accurate gestational dates, presence of multiple gestations, estimated fetal weights, detailed maternal pelvimetry, placental anatomy, amniocentesis results, maternal blood type and Rh factor, and prior documented obstetric complications. This information allows the obstetrician to anticipate complications of labor and delivery. It is difficult if not impossible to obtain these data in the ED while preparing for imminent delivery. Finally, in certain situations, cesarean section is the best way to ensure successful delivery. This surgical option is not available in the ED except in dire perimortem circumstances.

Epidemiology of Emergency Delivery

In 2004 the perinatal mortality rate in the United States was 6.2 per 1000 live births and fetal deaths (<20 weeks of gestation).³ Delivery complications and mortalities do occur with greater frequency in the ED, where the perinatal mortality rate is approximately 8 to 10%.⁴ There are multiple causes of the “high-risk” ED delivery profile. The ED is often selected by an obstetric population with unexpected complications. Antepartum hemorrhage, premature rupture of membranes (PROM), eclampsia, premature labor, abruptio placentae, precipitous delivery, malpresentation, and umbilical cord emergencies are overrepresented in the ED population.⁴

Psychosocial factors further skew the epidemiology of ED deliveries. Women who present with precipitous deliveries often have had little or no prenatal care.⁵ Pregnant women who have drug or alcohol problems or are victims of domestic violence represent a disproportionate number of patients who deliver in the ED. Women who are unaware or in denial of their pregnancies or immigrants without access to other medical care also present to the ED when labor begins.^6–8

Patient Transfer Considerations

Because of the high risk associated with ED delivery, patients should be transported to a facility that has obstetric and neonatal resources whenever possible. The management of a premature infant may require highly specialized intensive care that is unavailable at many community hospitals. The desire to transfer a woman with an impending high-risk delivery to such a facility should be tempered, however, by clinical and medicolegal judgment.9,10

Medicolegal Considerations

Transfer, with resultant en route delivery, can be disastrous for the mother and fetus. Such a transfer also violates federal law. The Consolidated Omnibus Reconciliation Budget Act (COBRA) of 1989 was based on an “inappropriate” obstetric transfer.¹¹ Federal law has identified labor as a condition unsuitable for transfer because of its unstable nature. Although the intent of this legislation is to protect women from medical abandonment because of financial reasons, COBRA runs the risk of forcing emergency physicians to occasionally perform difficult high-risk deliveries that might have better outcomes with transfer.¹²

Nursery Requirements

For many ED deliveries, labor will have progressed to a point at which tocolysis is contraindicated and delivery is imminent. In general, this is when the mother feels the urge to push or the head is crowning. Whenever possible, a neonatologist or pediatrician should attend high-risk preterm (<36 weeks of gestation) deliveries, and preparations for neonatal resuscitation and high-level nursery care should be initiated (Box 181-1).

BOX 181-1 Levels of Nursery Care

Level 1 Nurseries

These nurseries care for infants presumed healthy. In such units, screening and surveillance are primary responsibilities. Rooming-in units are encouraged, with emphasis on support of breast-feeding and assessment of parenting skills.

Level 2 Nurseries

These nurseries care for infants >30 weeks’ gestation and >1200 g who require special attention short of circulatory or ventilator support and major surgical procedures. A high percentage of the patients in such nurseries have had obstetric complications (e.g., birth trauma, fetal distress, and obstetric anesthesia).

Level 3 Nurseries

These nurseries are staffed and equipped to care for all newborn infants who are critically ill, regardless of the level of support required. They are regional institutions serving as referral centers for other nurseries and for this reason are often linked with transport services.

Perinatal Centers

A perinatal center provides services to high-risk mothers and to infants requiring level 3 nursery care. Ample data show a higher neonatal survival rate for high-risk pregnancies cared for in such centers.

Normal Delivery

Although the epidemiology and high complication rate associated with ED births demand caution, most are normal deliveries. Knowledge of normal labor and delivery mechanics aids safe vaginal delivery and facilitates the identification of complications.

Whenever a woman in the third trimester of pregnancy seeks treatment in the ED, the possibility that she is in labor must be considered. A wide array of nonspecific symptoms may herald the onset of labor. Abdominal pain, back pain, cramping, nausea, vomiting, urinary urgency, stress incontinence, and anxiety can be symptoms of labor. After 24 weeks’ gestation, any medical assessment should include the mother and the fetus because fetal viability becomes established near that time. In addition, given the generally high-risk nature of this population of patients and the abundance of body fluids that the health care provider and newborn are exposed to during delivery, serologic testing for infectious disease may be warranted. With the development of rapid bedside testing technology, human immunodeficiency virus (HIV) infection and hepatitis screening before delivery is indicated in a significant group of patients presenting with active labor.

Abdominal examination with Leopold’s maneuvers may confirm the lie of the fetus (Fig. 181-2). After labor has begun, particularly during the active phase of stage 1, Leopold’s maneuvers are difficult to use. The firm contractions of the uterus prevent the identification of fetal “small parts.” Other modalities of assessing the lie, such as ultrasonography, may be necessary if presentation remains in question.¹⁵

Figure 181-2 Leopold’s maneuvers. A, The first Leopold maneuver reveals what fetal part occupies the fundus. B, The second Leopold maneuver reveals the position of the fetal back. C, The third Leopold maneuver reveals what fetal part lies over the pelvic inlet. D, The fourth Leopold maneuver reveals the position of the cephalic prominence. (Modified from Willson JR, et al: Obstetrics and Gynecology, 9th ed. St. Louis, Mosby, 1991.)

Maternal examination also provides a rough guide to gestational age. At 20 weeks’ gestation, the uterine fundus reaches the umbilicus. Approximately 1 cm of fundal height is added per week of gestation until 36 weeks. At that time, the fundal height decreases as the fetus “drops” into the pelvis (Fig. 181-3). These estimates help establish gestational age rapidly.

Figure 181-3 Height of fundus by weeks of normal gestation with a single fetus. Dotted line indicates height after lightening. (Modified from Barkaukas V, et al: Health and Physical Assessment. St. Louis: Mosby; 1994.)

The accurate determination of the stage of labor depends on examination of the cervix. A sterile approach with use of sterile gloves, a sterile speculum, and povidone-iodine (Betadine) solution is indicated to prevent ascending infection, such as chorioamnionitis. On pelvic examination, the clinician should determine the following:

Effacement refers to the thickness of the cervix. A paper-thin cervix is 100% effaced.

Dilation indicates the diameter of the cervical opening in centimeters. Complete, or maximum, dilation is 10 cm.

Position describes the relationship of the fetal presenting part to the birth canal. The most common position of the head is occiput anterior.

Station indicates the relationship of the presenting fetal part to the maternal ischial spines (Fig. 181-4).

Figure 181-4 Fetal stations. The level of the ischial spines is considered 0 station. The silhouette of the infant’s head is shown approaching station +1. (Courtesy Ross Laboratories, Columbus, Ohio.)

Presentation specifies the anatomic part of the fetus leading through the birth canal.

In 95% of all labors, the presenting part is the occiput, or vertex. On digital examination, a smooth surface with 360 degrees of firm bony contours and palpable suture lines is noted. Palpation of the suture lines and the fontanels where they join allows the examiner to determine the direction the fetus is facing. Three sutures radiate from the posterior fontanel, and four radiate from the anterior fontanel (Fig. 181-5). The lateral margins are examined carefully for fingers or facial parts that indicate compound or brow presentations.

Figure 181-5 Bone landmarks of the fetal skull. (Modified from Willson JR, et al: Obstetrics and Gynecology, 9th ed. St. Louis, Mosby, 1991.)

When the clinician suspects rupture of membranes, a sterile speculum examination is performed. This may reveal pooling of amniotic fluid. Two tests to confirm the presence of amniotic fluid include a fernlike pattern when the fluid is allowed to dry on a microscope slide and the use of Nitrazine paper, which should turn blue, indicating an alkaline amniotic fluid (pH > 6). Although vaginal blood, cervical mucus, semen, and infection can interfere with results, sensitivities of both Nitrazine paper and ferning in detection of amniotic fluid are nearly 90%.¹⁶

Of note, if vaginal bleeding is evident, both digital and speculum examination of the pelvis should be deferred until an ultrasound study can be obtained to rule out placenta previa.

Second Stage of Labor

The second stage of labor is characterized by a fully dilated cervix and accompanied by the urge to bear down and push with each uterine contraction. The fetal station is advanced to +3, with crowning of the presenting part as expulsion begins. Stage 2 uterine contractions may last 1 or 2 minutes and recur after a resting phase of less than 1 minute. The median duration of this stage is 50 minutes in nulliparous women and 20 minutes in multiparous women. More rapid progression through stage 2 should be anticipated for low-birth-weight premature infants. A prolonged second stage of labor is defined as more than 3 hours in nulliparous women if regional anesthesia is administered, more than 2 hours in nulliparous women without anesthesia or in multiparous women with regional anesthesia, and more than 1 hour in multiparous women without regional anesthesia.¹⁷ Prolonged second stage of labor is associated with an increase in maternal complications, including postpartum hemorrhage, infection, and severe vaginal lacerations.¹⁸

Antenatal Fetal Assessment: The assessment of a woman in the third trimester includes an assessment of fetal well-being. After 24 weeks’ gestation, the fetal condition affects clinical decision-making. During labor and delivery, the identification of fetal distress and appropriate intervention can reduce fetal morbidity and mortality.

There are currently three methods of assessing a fetus in utero. Clinical monitoring, electrical monitoring, and ultrasonography all have a role in the assessment of the fetus. External electrical monitoring and ultrasonography merit consideration for use in the care of women laboring in the ED. The machinery for both technologies is portable and easy to use and can provide real-time information helpful for diagnosis of fetal distress and assistance with intrapartum decision-making.

Electronic Fetal Monitoring.: Intrapartum fetal assessment by electronic fetal monitoring is most useful during stage 1 of labor. Electronic fetal monitoring confirms true labor and may help diagnose fetal distress. Tracings of fetal heart rate and uterine activity provide information that in combination with clinical data can presage fetal distress due to hypoxia and provide a window for intervention.

Uterine activity is measured transabdominally by a pressure transducer, creating a recording of the contraction frequency. Because the measurements are indirect, the strength of the contractions correlates poorly with the tracing. The tracings are position and placement sensitive. Documentation of organized cyclic uterine contractions confirms the onset of labor and rules out Braxton Hicks contractions that are too disorganized to be registered in this manner. Premature onset of labor can also be diagnosed. Finally, this type of external electrical monitoring may be used to determine the efficacy of administered tocolytic agents.

Fetal heart rate tracings have several components that can be assessed: baseline heart rate, variability, accelerations, decelerations, and diagnostic patterns. Baseline heart rate, by definition, is the average fetal heart rate during a 10-minute period (in the absence of a uterine contraction) and is the most important aspect of fetal heart rate monitoring. Fetal bradycardia is defined as a baseline rate of less than 110 beats per minute; fetal tachycardia is defined as a baseline rate of more than 160 beats per minute.¹⁹

Variability can be instantaneous (beat to beat) or long term during intervals of 1 minute or more. Both types of variability are indicators of fetal well-being. Accelerations of heart rate are an important component of long-term variability. Accelerations occur during fetal movement and reflect an alert, mobile fetus. Brief periods of umbilical cord compression also can cause accelerations by decreasing the venous return and reflexively generating fetal tachycardia. Meanwhile, decreased variability may indicate fetal acidemia and hypoxemia or may be a side effect of a wide array of drugs. Analgesics, sedative-hypnotics, phenothiazines, and alcohol have been reported to cause decreased variability.

Decelerations in fetal heart rate are more complicated, and their interpretation should be integrated with the clinical situation. There are three types of deceleration: variable, early, and late (Fig. 181-6). These terms refer to the timing of the deceleration relative to the uterine contraction.

Figure 181-6 Deceleration patterns of the fetal heart rate (FHR). A, Early deceleration caused by head compression. B, Late deceleration caused by uteroplacental insufficiency. C, Variable deceleration caused by cord compression. (Modified from Lowdermilk DL, et al: Maternity and Women’s Health Care, 6th ed. St. Louis, Mosby, 1997.)

Variable and early decelerations are common. Present on more than 50% of all tracings, these heart rate changes can represent physiologic reflexes associated with head compression in the birth canal or intermittent cord compression. Variable decelerations that are persistent and repetitive usually indicate repeated episodes of umbilical cord compression. The resultant hypoxia and acidosis may cause fetal distress. Attempts to shift maternal and fetal weight off the umbilical cord by changing position are indicated. If these variable decelerations continue, the situation calls for efforts to hasten the delivery or, if obstetric backup becomes available, to perform an emergency cesarean section.

Late decelerations are more serious and most often indicate uteroplacental insufficiency. The tracing contours are generally smooth, with the heart rate nadir occurring well after maximal uterine contraction (typically 30 seconds or more afterward).¹⁹ The lag, slope, and magnitude of late decelerations correlate with increasing fetal hypoxia. Late decelerations are particularly ominous in association with poor variability, nonreactivity, and baseline bradycardia. When these findings are present, immediate obstetric consultation for delivery to prevent further hypoxia is indicated. The need for newborn resuscitation should be anticipated and preparation for critical care established for these deliveries. Overall, 30% of infants with late decelerations have good outcomes. The remaining 70% have suboptimal outcomes related to either the underlying pathologic condition or hypoxia.

Finally, the clinician should be aware of the significance of sinusoidal tracings. Tracings of this type have low baseline heart rates and little beat-to-beat variability. The sinusoidal tracing is an ominous finding that is often premorbid. The differential diagnosis includes erythroblastosis fetalis, placental abruption, fetal hemorrhage (trauma), and amnionitis.

Ultrasonography.: Ultrasonographic techniques have wide application in obstetric care. In the third trimester or during labor, ultrasonography can provide crucial information pertaining to impending delivery. When a technician and radiologist are available, the gestational age, biophysical profile, and amniotic fluid index as well as a survey of fetal and placental anatomy may be discerned (Table 181-1). The parameters of immediate interest in the ED are fetal viability (specifically in utero gestation and fetal heart rate), lie, and presentation. Ultrasonography may also reveal multiple gestations, allowing preparation and early communication with other specialists (from obstetrics, neonatology, and anesthesia). In 1991 the American College of Obstetricians and Gynecologists (ACOG) published recommendations regarding the indications for ultrasonography in the third trimester (Box 181-2). A 2- to 5-MHz transducer is appropriate for all bedside transabdominal sonographic assessments. Transvaginal ultrasonography is relatively contraindicated in the peripartum period, particularly in the cases of PROM and placenta previa.²⁰

Table 181-1

Biophysical Profile: 30 Minutes of Ultrasonographic Observation

ELEMENT ASSESSED	NORMAL SCORE = 2	ABNORMAL SCORE = 0
Fetal heart rate reactivity	2 accelerations >15 beats/minute for >15 seconds	<2 accelerations
Amniotic fluid index	1 pocket >1 cm in orthogonal planes	No large pockets
Fetal muscle tone	1 episode of active flexion-extension with full return to flexed posture	<1 episode or slow, incomplete actions
Body movements	3 discrete moves	≤2
Breathing motions	1 episode of fetal breathing of at least 60 seconds in duration during 30 minutes of observation	No breathing activity or The absence of 1 episode of fetal breathing of at least 60 seconds in duration during 30 minutes of observation

Delivery: As stage 2 of labor progresses, preparation for delivery should be under way. A radiant warmer should be available and heated. Neonatal resuscitation adjuncts, such as a towel, scissors, umbilical clamps, bulb suction, airway management equipment (oxygen, bag-mask device with appropriate-sized masks, and endotracheal intubation and suctioning equipment for meconium), and equipment to achieve vascular access, should be available. Most deliveries require only basic equipment to cut and clamp the umbilical cord, to suction the mouth and nose, and to dry and stimulate the infant. A nurse should be at the bedside to coach and to provide reassurance to the mother.

The mother is placed in the dorsal lithotomy position and prepared for delivery. The Sims position, or left lateral position with knees drawn toward the mother’s chest and back to the physician, is also an acceptable position for delivery. The vulva and perineum are cleared and gently scrubbed with sterile water or saline, directing all mucoid debris and feces away from the introitus. A repeated sterile examination to assess labor progression and to confirm presentation may be performed. Firm digital stretching of the perineum, particularly posteriorly, may prevent tears and lacerations later in delivery.

Controlled, coordinated expulsion with coaching to sustain each push aids with crowning and delivery of the head. When the fetus is crowning, care is exercised to have the delivery occur in a slow, controlled manner. Precipitous delivery is more likely to cause maternal injuries, such as perineal, rectal, urethral, labial, vaginal, and uterine lacerations, and fetal injuries.²¹

The most vulnerable moment is when the fetal head begins to stretch and distend the perineum. Instructing the mother to pant and not push slows the passage of the head and the shoulders as indicated. Calm communication between the physician and the mother is the best way to maintain control of the delivery. With a controlled delivery, routine performance of an episiotomy is not recommended.

One described technique to potentially decrease the rate of maternal injury is the modified Ritgen maneuver.²² In the modified Ritgen maneuver, a towel-draped, gloved hand is used to stretch the perineum and gently exert pressure on the chin of the fetus. The second hand puts pressure on the occiput superiorly, guiding the head into slight extension. When the head is at the perineum, this slight extension of the head promotes delivery by positioning the head so that its smallest diameter passes through the pelvic outlet and perineum.

After the head is delivered, the physician allows the head to rotate toward the maternal thigh and clears the fetal face and airway. Coordination with the mother is important to prevent uncontrolled fetal expulsion.

Next, the shoulders, usually anterior shoulder first, clear the perineum. The shoulders often deliver spontaneously, with little effort by the physician. First, gentle downward traction on the head promotes delivery of the anterior shoulder. A subsequent upward motion pulls the posterior shoulder through the pelvic outlet, minimizing maternal trauma. If delay occurs in delivery of the shoulders, the potential for shoulder dystocia should be considered.

As the infant clears the perineum, attention focuses on the umbilical cord. The infant should be kept low or at the level of the perineum to promote blood flow into the infant from the placenta. The cord is clamped and cut. Clamps should be placed 4 or 5 cm apart, with the proximal clamp 10 cm from the infant’s abdomen. An adequate umbilical stump is important for venous access if the child requires resuscitation. Suctioning of the nose and mouth at this time may reduce secretions that can cause increased airway resistance.

The infant is now clear of the mother and can be wrapped in towels and moved to the warmer. Gentle drying with a towel and suctioning usually provide adequate respiratory stimulation. If not, flicking the soles of the feet and rubbing the back are other modalities. Apgar scores at 1, 5, and 10 minutes after birth should be documented.

Episiotomy.: Previously, the need for episiotomy in normal deliveries was an area of controversy. The original potential benefit of episiotomy included the substitution of a straight surgical incision for a ragged, uncontrolled traumatic laceration. Theoretically, the surgical approach decreased the incidence of severe rectovaginal tears. This rationale led to widespread routine episiotomy, with a medial incision used in the United States and a mediolateral incision used in the Commonwealth countries.

Recent literature has shown that both types of incisions increase maternal morbidity, and they are no longer recommended for uncomplicated deliveries. Women receiving episiotomies have been shown to have a higher incidence of perineal trauma and maternal blood loss during delivery and more pelvic pain, sexual dysfunction, and urinary incontinence in the postpartum period.²³

Episiotomy should be performed only for specific indications, such as shoulder dystocia or breech delivery. When the decision is made to use an episiotomy, the procedure should be done before excessive stretching of the perineal muscles occurs but near the time of delivery to avoid excessive bleeding. Common practice is to cut the episiotomy when the head is visible during a contraction and the introitus opens to a diameter of 3 or 4 cm. Most authors currently recommend a mediolateral incision to avoid perineal tears and rectal involvement; this is particularly true for a complicated delivery in which lacerations extending the surgical incision are likely (Fig. 181-7).

Figure 181-7 A mediolateral episiotomy incision is preferred to a strictly midline incision. (Redrawn from www.aurorahealthcare.org/healthgate/images/exh44028a_ma.jpg.)

Table 181-2 summarizes some of the adjuncts used in normal labor and delivery, with recommendations for their use in the high-risk setting of an ED delivery.

Table 181-2

Risk-Benefit Analysis of Routine Adjuncts to Normal Labor and Delivery

Third Stage of Labor

The third stage of labor involves the delivery of the placenta and is a time of observation of the patient with frequent checks of the tone and height of the uterine fundus. Signs of placental separation include the following:

The uterus becomes firmer and rises.

The umbilical cord lengthens 5 to 10 cm.

There is a sudden gush of blood.²⁴

These signs usually occur within 5 to 10 minutes of the delivery of the infant but may extend to 30 minutes. The risk of postpartum hemorrhage increases beyond 18 minutes and is in fact up to six times more likely after 30 minutes.²⁵ Although the placenta may be delivered expectantly, active management reduces the length of the third stage of labor and thereby decreases the risk of postpartum hemorrhage. Active management includes the administration of uterotonics, gentle traction of the clamped umbilical cord with mild pressure applied above the symphysis pubis, and uterine massage after delivery.²⁶ Be aware that any attempt to deliver the placenta before it separates is contraindicated.

Examination of the placenta and umbilical cord is an essential part of the delivery process. Abnormalities of the cord should be noted at this time. Also, a segment of the umbilical cord should be kept available as a source of cord blood.

Normally a three-vessel structure, the umbilical cord is filled with a connective tissue known as Wharton’s jelly and is approximately 50 to 60 cm long and 12 mm in diameter. Normal architecture places the two umbilical arteries on either side of the single umbilical vein. A two-vessel cord (one umbilical artery) occurs in 1 of 500 deliveries, is more common in African Americans, and is a result of aplasia or atrophy. Approximately 30% of two-vessel cord infants have congenital defects. An association also exists between fetal structural anomalies and placental vascular occlusion or thrombosis.²⁷

The placenta should also be examined for abnormalities. Clots adherent to the uterine aspect may indicate placental abruption. Accessory lobes (succenturiate placenta if completely separate) and abnormal cord insertion are common abnormalities. The umbilical cord and placenta routinely should be held for pathologic review.²⁸ The discovery of an incomplete placenta or membranes should alert the emergency physician to the possibility of postpartum complications and should be documented.

Fourth Stage of Labor

The fourth stage of labor refers to the first hour after delivery of the placenta and is a critical period because postpartum hemorrhage is most likely to occur during this time. Thus careful examination and repair of any vaginal lacerations should be performed. The cervix and vaginal fornices are visually inspected to avoid missing deep lacerations as a result of delivery.

At this point, oxytocin is infused to promote contraction of the uterus and to control hemorrhage. The uterus is evaluated frequently for tone and massaged transabdominally if any sign of relaxation exists. Oxytocin should not be given before delivery of the placenta because this may result in the trapping of placental fragments or may hinder the delivery of an undetected twin.

Specific Disorders

Third-Trimester Complications Associated with Delivery

Obstetric problems in the third trimester often result in the initiation of labor. Premature labor, PROM, and third-trimester bleeding are relatively common complications. The fundamental question to be addressed in these settings is whether the fetus would fare better in utero or delivered.

Premature Labor

Perspective.: Premature or preterm labor and fetal immaturity are the leading causes of neonatal mortality. Preterm labor is defined as uterine contractions with cervical changes before 37 weeks of gestation. Women with premature labor are a heterogeneous group. Many underlying conditions result in preterm labor, which accounts for 9.6% of all pregnancies but 70% of all perinatal mortality.²⁹ Factors linked to this problem include substance abuse, history of preterm delivery, multiple gestations, placental anomalies, infections, and lifestyle or psychosocial stressors³⁰ (Box 181-3). The unexpected nature of premature labor often results in an ED visit. When delivery is not imminent, the patient can be moved to the obstetrics unit for further care.

Clinical Features.: The diagnosis of preterm labor requires the identification of uterine activity and cervical changes before 37 weeks of gestation. Early maternal signs and symptoms include an increase or change in vaginal discharge, pain resulting from uterine contractions (sometimes perceived as low back pain), pelvic pressure, vaginal bleeding (usually bloody show), and fluid leak.

Diagnostic Strategies.: If uterine contractions and cervical changes are present and the estimated fetal weight on ultrasonography is less than 2500 g, the diagnosis of premature labor is likely. The differentiation of false labor (Braxton Hicks contractions) from true labor is best done by electrical monitoring. Ultrasonography may aid in the diagnosis because fetal breathing movements make the diagnosis of false labor unlikely. The initial evaluation of a woman with possible preterm labor includes urinalysis, complete blood count, and pelvic ultrasonography. If delivery is not imminent, these studies can be performed in the ED or obstetrics area, whichever would provide the best monitoring. When possible, these patients should be transferred to a perinatal center with an associated intensive care unit.

Management.: A viable fetus and healthy mother are indications for medical management directed toward the prolongation of gestation. Preterm labor should not be postponed with medical management in the cases of fetal compromise, major congenital anomalies, intrauterine infection, placental abruption, eclampsia, significant cervical dilation, or, most important, PROM.³¹

The treatment of preterm labor involves multiple modalities. Tocolytics and fetal maturation therapy combined with bed rest and hydration are used in the hope of prolonging pregnancy (Box 181-4). These patients optimally should be transferred to an appropriate center before delivery whenever possible because medical management fails in more than 25% of preterm patients in whom it is attempted.³²

Tocolysis: The two classically used tocolytics are magnesium sulfate and beta-mimetic drugs. Other medications that have been shown to be effective include prostaglandin synthetase inhibitors (nonsteroidal anti-inflammatory drugs [NSAIDs]) and calcium channel blockers.³³ When they are indicated and in coordination with an obstetric consultant, tocolytics initiated in the ED may arrest premature labor, preventing imminent delivery in 75 to 80% of patients for 48 to 72 hours.²⁹

Magnesium Sulfate: Magnesium sulfate competitively inhibits calcium uptake into smooth muscle and allows relaxation. The efficacy of magnesium sulfate as a tocolytic agent has not been clearly established.³⁴ Women treated with magnesium require monitoring. Magnesium produces respiratory and neurologic depression at elevated levels, exacerbated by renal insufficiency. Pulmonary edema and cardiac dysrhythmias have also been reported.²⁹ These effects can be reversed rapidly by the administration of calcium-containing solutions (i.e., 1 g of 10% calcium gluconate solution) (Table 181-3).

Table 181-3

Drug and Labor Interactions

DRUG	EFFECT ON LABOR
Barbiturates	Can stop labor in anesthetic doses
Alcohol	Decreases oxytocin release, smooth muscle relaxant
Cocaine	Increased prematurity, placental infarction
Caffeine or aminophylline	Increased duration of labor
Narcotics	Increased latent phase, slow dilation (minimal effect once in active labor)
Atropine, scopolamine	Lower uterine segment relaxation, decreased frequency of contractions
Halothane	Strong inhibition of labor
IV nitroglycerin	Profound uterine relaxation