19.1 Labor Dystocia

Uterine Dystocia

The labor complication in which lack of cervical dilation occurs due to insufficient contraction strength, frequency, or duration is uterine dystocia (Wu et al., 2017).

Figure 19.2 shows monitor tracings associated with uterine dystocia. In a normal contraction pattern, the upper uterine muscles shorten during the contraction to elongate the lower uterine segment, which causes dilation, effacement, and descent of the fetal head. (Figure 19.3) shows how the muscle fibers of the uterus work together.

Figure 19.2 Fetal Monitor Tracings of Uterine Contraction Patterns These monitor tracings represent the common uterine contraction patterns seen in labor over 15 minutes. Tracing 1 represents an inadequate pattern, with too few contractions. Tracing 2 represents a tachysystole pattern, with too many contractions that lack strength and duration. Tracing 3 represents a normal contraction pattern, with five contractions. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Figure 19.3 Uterine Muscle Structure The muscle structure of the uterus enables contractions to shorten the upper uterine segment and stretch the cervix open. This is demonstrated by the white lines in the picture. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Multiple factors cause inadequate uterine contraction activity. Causes related to the pregnant person are chorioamnionitis, dehydration and malnutrition, exhaustion, and emotional stress. Chorioamnionitis can cause the uterine muscle to inadequately contract due to the inflammatory process of infection. Pregnant persons with long labors who are allowed little to eat or drink can become exhausted, hypoglycemic, and dehydrated, preventing the uterine muscles from contracting properly. Emotional stress occurs when fear, pain, or inability to relax releases stress hormones, such as cortisol, that inhibit proper oxytocin production (Aristizabal, 2019). A fetal cause of inadequate contraction patterns can be malposition. The fetus presenting in the occiput-posterior or occiput transverse position creates a larger diameter to pass through the pelvic inlet, making labor progression difficult. The role of the nurse is to encourage hydration, assist with frequent movement and position changes, and provide emotional support to alleviate fear and stress in the laboring person.

Multiple gestation, large for gestational age, and polyhydramnios (an excessive amount of amniotic fluid) distend the uterus and decrease the strength of the contractions, causing uterine dystocia. Grand multiparity and prolonged labor are associated with a uterus too tired or overstretched to contract efficiently. Uterine anomalies, such as bicornuate and unicornuate uteri, are associated with uterine muscle dysfunction. Epidural anesthesia may decrease uterine contraction strength and frequency and has been linked to a nonengaged fetal head (Penuela et al., 2019).

Uterine dystocia can also occur in second stage labor. When the cervix is fully dilated and the fetal head has descended, most laboring persons feel an overwhelming urge to push. The fetus is born by the expulsive strength of the uterine contractions and the maternal pushing effort. Dystocia may occur because epidural anesthesia reduces the urge to push. Second stage dystocia can also result from the same risk factors that cause first stage uterine dystocia. New guidelines for second stage labor recommend that a nulliparous person push at least 3 hours and a multiparous person push at least 2 hours prior to diagnosing dystocia (American College of Obstetricians and Gynecologists [ACOG], 2024). The guidelines do not specify any difference in length with or without an epidural. The role of the nurse during the second stage, especially during dystocia, is to provide support and assist in the pushing process.

Pelvic Dystocia

A labor complication that occurs when the size of the fetal head is larger than the size of the maternal pelvis due to a small capacity of the pelvic inlet, midpelvis, or pelvic outlet is called pelvic dystocia. In a normal labor, the fetal head descends and engages in the pelvic inlet. As the fetus passes through the pelvis, the head flexes and rotates to the occiput-anterior (OA) position in the midpelvis. The fetal head enters the pelvic outlet in a flexed OA position and is born by the extension of the fetal head. If any part of the pelvis is too small for the fetal head, these cardinal movements cannot occur. At times, the power of the contractions can be adequate, but because of the inability of the fetal head to descend, cervical dilation and effacement stall (Cohen & Friedman, 2023).

The normal pelvic inlet should allow the passage of a fetal head diameter of approximately 9.5 centimeters (cm) (Figure 19.4). Therefore, if the pelvic inlet is less than 10 cm, it could cause inability of the fetal head to engage and pass through the inlet.

Figure 19.4 Pelvic Inlet The pelvic inlet must be adequate for the fetal head to enter and pass through to avoid pelvic dystocia. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Midpelvis dystocia is more common than pelvic inlet dystocia. The midpelvis is measured by the distance between the ischial spines and should average more than 9 cm (Figure 19.5). When the nurse is performing a cervical exam during labor, the ischial spines are the landmark for determining station. If the ischial spines are encroaching and prominent, the nurse is aware that a midpelvis dystocia could occur. With a smaller midpelvis, the fetal head engages but is unable to flex or rotate anteriorly. Molding and caput succedaneum are seen with this dystocia.

Figure 19.5 Midpelvis A midpelvis dystocia occurs when the ischial spines are prominent and encroaching. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Pelvic outlet dystocia is seen when the ischial tuberosity distance is less than 8 cm (Figure 19.6). When the pelvic outlet is contracted or too small, the fetal head can become malpositioned as the fetus attempts to turn the head to find the path of least resistance to progress through the pelvis. Extreme caput succedaneum can occur. Pelvic outlet dystocia can lead to prolonged pushing, forceps birth, or cesarean birth.

Figure 19.6 Pelvic Outlet A pelvic-outlet dystocia occurs when the ischial tuberosities are encroaching and not allowing descent of the fetal head. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Fetal Dystocia

The labor complication in which the fetal head is unable to navigate through the pelvis is fetal dystocia. Reasons for fetal dystocia can be a persistent occiput posterior or transverse, face, or brow presentation. Occiput posterior or transverse positions can stall cervical dilation due to lack of even pressure exerted on the cervix. These positions can also lead to failure of the presenting part to descend. A face presentation occurs when the neck is hyperextended and the chin, also called the mentum, is presenting. This presentation, occurring in only 0.1 percent of births, is caused by prematurity, pendulous maternal abdomen, fetal malformations (anencephaly), and polyhydramnios (Mohammed & El-Chaar, 2022). Some face and brow presentations are seen with large fetuses and contracted pelvis inlets. A vaginal delivery is possible if the chin is directed at the maternal symphysis pubis (mentum anterior) (see Figure 15.8). It is impossible for a fetus to navigate the pelvis if the chin remains posterior and pointing toward the maternal back (mentum posterior); a cesarean birth is necessary (Mohammed & El-Chaar, 2022). The role of the nurse is to support and educate the laboring person and family regarding the possible changes in birth plan to a forceps or cesarean birth.