Normal Vaginal Deliveries

Liza G. Smith

OVERVIEW

Most women in labor present directly or are triaged to an obstetric unit so births occurring in the prehospital or emergency department (ED) setting are rare. Deliveries that do occur in the ED are associated with increased risk of neonatal and maternal morbidity and mortality.¹ The overall perinatal mortality rate in the United States for births at 28 weeks’ gestation or greater has remained steady at 0.6% (6 deaths per 1,000 births) for almost a decade.² Data on prehospital and ED deliveries are limited; however, the rates of perinatal mortality are reported to be as high as 8% to 10%.³ A study of accidental deliveries in the prehospital setting demonstrates neonates are more likely to require admission to the neonatal unit and have a higher perinatal mortality rate than controls (51.7 vs. 8.6/1,000 deliveries, respectively).⁴

The high-risk epidemiology of ED deliveries is multifactorial but primarily due to psychosocial factors. Data indicate that women who have unplanned deliveries in the prehospital or ED setting are more likely to be from low socioeconomic status.⁵ There is also evidence that these mothers have higher rates of smoking, illicit drug use, and poor or absent prenatal care.⁶ Women who have substance use disorder, who are victims of intimate partner violence, who are undocumented, or who are otherwise without access to routine medical care are overly represented in the population of women who deliver in the prehospital and ED setting.

Emergency medicine (EM) providers must be able to identify when a woman is in labor as well as determine if delivery is imminent and be prepared to manage that delivery while anticipating myriad potential complications. Providers must be able to manage both normal and complicated deliveries as well as maternal and neonatal resuscitation if required. It is critical that the ED has all necessary equipment for delivery of the fetus (Table 21.1), resuscitation of the newborn, and aftercare of the mother. Ideally, this equipment is in a preassembled precipitous vaginal delivery kit that is ready to use when needed.

CLINICAL FEATURES

When a patient presents to the ED with suspected labor, the provider should obtain a focused history and physical examination to determine the stage of labor and whether delivery is imminent, as well as identify any risk factors for potential complications.

History

The initial history should include maternal parity, gestational age, due date, whether there was prenatal care during the pregnancy, duration and frequency of uterine contractions, and whether the patient feels the urge to push. Determining the approximate gestational age is paramount both to
assess potential fetal viability and to anticipate possible neonatal resuscitation needs in the event of a preterm delivery (defined as occurring at <37 weeks’ gestation). The patient should be asked about the presence and timing of rupture of membranes, presence of vaginal bleeding, complications with this pregnancy, history of prior complicated or precipitous deliveries, as well as any symptoms of infection. Clinicians should also obtain a basic medical and surgical history, list of current medications and allergies, and inquire about substance abuse.

TABLE 21.1 Basic Vaginal Delivery Kit Equipment List^a

Sterile gloves and gown

Sterile towels and a large sterile drape

4 × 4 sterile gauze sponges

Rubber suction bulb

Two umbilical cord clamps

Sterile scissors

Clean towels or blankets to dry and swaddle the infant

A red top tube (for collecting fetal blood from the placental end of the cut umbilical cord)

A basin for the placenta

Two sterile Kelly clamps

18 gauge and 20 gauge needles (for injecting lidocaine if needed)

5 cc and 10 cc syringe (for injecting lidocaine if needed)

Biohazard bags with ties (for wet/bloody clothing and sheets)

^aStandard neonatal resuscitation equipment should also be available including neonatal warmer.

PHYSICAL EXAMINATION

Gestational Age

If the patient is not aware of the gestational age, the clinician can assess fundal height to obtain a rapid estimate; however, this measurement is only accurate after 20 weeks’ gestation. Fundal height is measured in centimeters from the pubic symphysis to the top of the fundus (cm = weeks of gestation ± 2 weeks). The fundus reaches the level of the umbilicus at approximately 20 weeks, so if the fundus is above this level, it is an approximate indication of fetal viability. Maternal obesity can interfere with the accuracy of this estimate. If bedside ultrasound is available, the clinician can measure a biparietal diameter or femur length to provide an alternative assessment of gestational age.

Maternal and Fetal Vital Signs

The evaluation of suspected labor in a patient of greater than 20 weeks’ gestation should begin with obtaining both maternal vital signs (temperature, heart rate, blood pressure, respiratory rate, and oxygen saturation) and fetal heart rate (FHR). The normal FHR is in the range of 110 to 160 bpm.⁷^,⁸ FHR can be obtained by fetal Doppler or by bedside ultrasound, and measurements outside the normal range in a viable fetus should prompt emergent obstetric evaluation.

The clinician should perform a general physical examination, making note of maternal fever, tachycardia, or blood pressure abnormalities. Lying supine can decrease venous return to the heart in the gravid patient due to aortocaval compression, resulting in hypotension in the mother and decreased blood supply to the fetus. Efforts should be made to minimize the length of time the patient remains in this position, preferentially maintaining a left lateral decubitus position or manually displacing the uterus, particularly if the patient is hypotensive or there are signs of fetal distress. The provider should evaluate for abdominal and uterine tenderness in addition to determining the lie of the fetus, ideally assessed by bedside ultrasound.

Fetal Lie

Fetal lie refers to the orientation of the fetus in relationship to the longitudinal axis of the uterus (Figure 21.1). The most common fetal lie is longitudinal, in which the long axis of the fetus is in the
same orientation as the longitudinal axis of the uterus.⁹ In a longitudinal lie, a fetus can be in either cephalic (head down) or breech (buttock down) presentation. Fetal lie can also be transverse, in which the fetus is oriented perpendicularly to the longitudinal axis of the uterus, or oblique, which is anywhere in between transverse and longitudinal. In a singleton gestation, only fetuses oriented in a longitudinal lie can be safely delivered vaginally.⁹

Figure 21.1: Fetal lie. A, Longitudinal lie. B, Transverse lie. (From Snelgrove-Clarke E, Budin W. Labour and childbirth. In: Evans RJ, Brown YM, Evans MK, eds. Canadian Maternity, Newborn & Women’s Health Nursing. 2nd ed. Philadelphia, PA: Wolters Kluwer; 2014:586.)

Pelvic Examination

The pelvic examination begins with visual inspection of the external genitalia. The clinician should note any lesions, such as those suggestive of active herpes simplex infection, which are a contraindication to vaginal delivery. Labor may begin with the expulsion of the cervical mucus plug, which may contain some blood and is termed a “bloody show.” This is associated with only a small amount of blood mixed with copious mucus. Signs of more significant bleeding should raise concern for placenta previa and necessitates ultrasound examination to determine the location of the placenta prior to either a speculum or digital examination.

In the absence of bleeding, the pelvic examination should proceed with a sterile speculum examination to evaluate whether the membranes have ruptured. The speculum examination should be performed without lubrication because lubricant gel can interfere with both nitrazine and fetal fibronectin testing. The vaginal pH is typically 4.5 to 5.5, and nitrazine paper will not exhibit color change when exposed to routine vaginal secretions. The pH of amniotic fluid is 7.0 to 7.4 and will turn nitrazine paper a dark blue. The presence of lubricant, blood, Trichomonas vaginalis infection, or semen can give a false-positive result for both nitrazine and fetal fibronectin tests.¹⁰^,¹¹ The presence of ferning, visualization of sodium chloride crystals as amniotic fluid dries on a microscope slide under low power, is another test used to confirm membrane rupture (Figure 21.2).¹² The finding of greenish or brownish fluid in the vaginal vault indicates the presence of meconium, often a marker of fetal distress.

Prelabor rupture of membranes (PROM) is the rupture of the fetal membranes before the onset of labor. In most cases, PROM occurs near term, but when PROM takes place before 37 weeks’ gestation, it is known as preterm PROM. Clinicians should not perform a digital cervical examination on patients with preterm PROM because this may hasten the progression to active labor and increase the risk of infection.¹⁰

Digital Vaginal Examination

At term, the health care provider should next perform a digital vaginal examination to further assess the stage and progression of labor. If rupture of membranes is suspected or confirmed during labor, the clinician may still perform a digital examination, but it becomes important to minimize subsequent vaginal examinations because each digital examination increases the risk of infection. This procedure is performed wearing a sterile glove and inserting the index and middle fingers into the vaginal canal. The clinician evaluates for cervical dilation, which refers to the diameter of the cervical opening in centimeters (from closed or “fingertip” to 10 cm when fully dilated). This measurement is obtained by determining the distance between the examiner’s index and middle
fingers, with each abutting the edge of the cervix at its widest point. The amount of cervical dilation helps the provider determine the stage and progression of labor.

Figure 21.2: Ferning pattern of amniotic fluid dried on a microscope slide. (From Haase J, Ogglesby E, Lewis JA, Black JJ. Fertility challenges. In: Evans RJ, Brown YM, Evans MK, eds. Canadian Maternity, Newborn & Women’s Health Nursing. 2nd ed. Philadelphia, PA: Wolters Kluwer; 2014:339.)

Effacement

With labor progression, the cervix softens and thins, a process known as effacement. Effacement is described as a percentage of cervical length, with 0% being a thickness of 2 cm or greater and 100% when there is minimal, or essentially no, thickness remaining. The estimate of cervical effacement is less reproducible among examiners, but generally 80% or greater effacement is required for the diagnosis of active labor.⁹

Fetal Presentation

The clinician should also evaluate fetal presentation, which refers to the fetal part that is directly palpable through the cervix (Figure 21.3). For a fetus in a longitudinal lie, the presentation can be either cephalic (head down) or breech (buttocks down). With cephalic orientation, presentation is further classified by which bony part of the skull is directly palpable. If the leading bony part is the occiput, the presentation is known as “vertex.” In a vertex presentation, the provider will palpate a smooth surface with underlying bony contours and suture lines. The orientation of the suture lines allows the provider to determine the direction the fetus is facing, known as “attitude.” Attitude is described relative to the direction of the occiput, with most oriented as occiput anterior (OA), or rotated just left (LOA) or right (ROA) of this orientation (Figure 21.3).⁹

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