Abnormal Labor in Obstetrics: Recognition and Management

Etiology

Normal labor progression requires consideration of the 3 "Ps," representing power, passage, and passenger. Power refers to uterine contractions and maternal expulsive efforts. The passage is the maternal pelvis, and the fetus is the passenger. Abnormal labor progression may be related to 1 or more of these factors. The size, position, and presentation of the fetus and the adequacy of the maternal pelvis are tested as uterine contractions provide propulsion. Asynclitism or extension of the fetal head, occiput posterior or transverse positions, and mentum or brow presentations may contribute to or be the sole etiologies of abnormal labor progression or dystocia.[7] Labor abnormalities due to unfavorable fetal or maternal pelvic dynamics may require a cesarean delivery.[8]

Uncommonly, a Bandl ring may be associated with protracted or arrested labor. A Bandl ring constricts between the thicker upper contractile and thinner lower uterine segments. Why this constriction develops during parturition is unclear—although prolonged labor and labor dystocia have been suggested as possible causes.[9]

Risk Factors Associated with Abnormal Labor

Maternal Factors

• Advanced maternal age
• Bandl ring
• Chorioamnionitis
• Epidural analgesia
• Gestational diabetes
• Hypertensive disorders
• Inadequate uterine contractions
• Lack of supportive care during labor
• Large weight gain in pregnancy
• Non-gynecoid maternal pelvimetry
• Nulliparity
• Poor hydration and nutrition during labor
• Postterm pregnancy
• Short stature
• Obesity
• Labor induction

 Fetal Factors

• High fetal station at full cervical dilation
• Macrosomia
• Malpresentation
• Fetal anomalies
• Nonreassuring fetal heart rate tracing [10]

Epidemiology

Abnormalities of labor are common worldwide. Pelvic shape varies significantly among women, and the fit between the maternal pelvis and fetus is exceptionally tight, unlike in other primates.[11] Approximately 20% of all labor involves protraction and/or arrest disorders. Disorders of labor are the most common reason for primary cesarean sections.[12] Abnormal labor involving true labor dystocia can result in fetal and/or maternal injury and even death. The trend toward more cesarean sections in developed countries has drawn attention to initiatives to minimize primary cesarean sections safely. In this regard, guidelines have been developed to implement more conservative management strategies for labor's first and second stages.[13]

There is currently no evidence-based consensus on what constitutes arrest during the latent phase of labor. Therefore, according to ACOG, in cases where both maternal and fetal conditions remain reassuring, cesarean delivery solely due to a prolonged latent phase should be avoided. For patients undergoing labor induction, the term “failed induction” is more appropriate when there is no cervical change during the latent phase, rather than labeling it as latent phase arrest. A prolonged first stage of labor may result in adverse outcomes for both mother and neonate.[5]

After the delivery of the fetus, the third stage of labor culminates in the delivery of the placenta. Abnormalities in the third stage can lead to postpartum hemorrhage requiring blood transfusions and, at times, resulting in maternal morbidity and mortality. Postpartum hemorrhage affects approximately 5% of all deliveries. The mean duration of the third stage of labor is 5 to 6 minutes when using active management, and 90% of the third stages take less than 10 minutes. Postpartum hemorrhage is more likely when the third stage lasts more than 18 minutes and significantly more likely when the third stage lasts over 30 minutes.[14] 

Pathophysiology

The pathophysiology of abnormal labor is poorly understood. Friedman initially established a labor curve for the expected timeframe of the first stage of labor; however, it has since been contemporized by Zhang et al.[15] Recent reference graphs indicate that the latent phase of labor is much longer than initially thought, and the active stage of labor begins at 6 cm of cervical dilation. Induced labor tends to have a longer latent phase in the first stage of labor when compared to spontaneous labor. However, the active phase of the first and second stages does not vary significantly, regardless of whether labor is spontaneous or induced. Insufficient uterine activity is the most common reason for a labor abnormality in the first stage of labor.[16] 

Labor is a physically intensive process, and prenatal exercise may play a role in increased uterine contractility. Increased physical activity levels have been associated with higher levels of oxytocin and decreased need for induction and augmentation of labor.[17] Maternal inactivity during pregnancy may be associated with prolonged labor. Results from a prospective cohort study showed that patients who were physically active during pregnancy were less likely to have a prolonged latent phase of labor and more likely to have a shorter active phase of labor.[17] For these and other reasons, regular prenatal exercise is highly encouraged.

Toxicokinetics

Oxytocin is a key pharmacologic agent in the augmentation of inadequate uterine contractions and, thus, in treating abnormal labor; it is 1 of the most commonly used medications in obstetrics. Exogenous oxytocin responsiveness typically commences at 20 weeks of pregnancy and increases with advancing gestational age until 34 weeks, when it appears to plateau.[18] Oxytocin has a short plasma half-life of 3 to 6 minutes and is utilized during labor as a continuous intravenous infusion.

Due to the high risk of patient harm when used in error, oxytocin is a high-alert medication.[19] Adverse maternal effects associated with oxytocin use in labor include flushing, nausea, vomiting, headache, tachycardia, and hypotension.[20] Maternal water retention and hyponatremia rarely occur due to oxytocin use and only with extended exposures to high doses of oxytocin, mainly if administered in hypotonic solutions. Hyponatremia is due to oxytocin's structure being similar to vasopressin's, causing cross-reactions with renal vasopressin receptors.[21] Uterine tachysystole commonly occurs as a result of oxytocin administration during labor. Tachysystole is 6 or more contractions in a 10-minute window, averaged over 30 minutes. Without adequate time for uterine relaxation between contractions, there is a potential for decreased fetal oxygenation.[20] 

History and Physical

Labor begins with regular, painful uterine contractions, resulting in cervical effacement and dilation. An essential piece of the patient history to obtain is the start time of contractions and their occurrence interval. An abdominal examination is a critical component of an obstetric examination, providing an estimated fetal weight and an assessment of fetal presentation. Continuous monitoring of uterine activity discerns how frequently contractions occur. Internal pressure catheter monitoring measures the actual strength of uterine contractions.

Fetal heart rate tracing may provide reassurance of fetal well-being throughout the labor process; however, the interpretation is highly varied and not diagnostic of fetal acidemia. Digital vaginal exams, conducted at different intervals throughout labor, assess maternal pelvimetry, bony pelvis shape and capacity, as well as cervical effacement and dilation. Serial digital exams are used to determine the fetal position, station, and descent of the presenting part, which is crucial in assessing the normal or abnormal progression of labor.[22]

Evaluation

Determining the progression of labor is a critical component of intrapartum care. Maternal uterine activity is assessed by manual palpation, external tocodynamometry, or monitoring with an intrauterine pressure catheter. Using external tocodynamometry, target uterine activity is 3 to 5 contractions in a 10-minute window. Effective contractions last 30 to 40 seconds. Intrauterine pressure assessment using a catheter is commonly used to measure the strength or intensity of uterine contractions in patients with ruptured membranes. This technique involves inserting a catheter through the cervix and into the uterus, which allows for direct measurement of intrauterine pressure. This monitoring employs Montevideo units (MVUs) as measurements of contraction intensity. MVUs are calculated by adding the sum of the net contraction pressures over 10 minutes.

Adequate uterine activity is targeted at 200 to 250 MVUs.[23] Although this method of assessing uterine contractions has limitations, a more valuable and accurate system has yet to be devised. Electrohysterography is a recent technique that uses externally applied abdominal electrodes to monitor and record the electrical voltages generated by myometrial contractions. This method of assessing uterine contractility is not currently part of standard clinical practice.[23]

Evaluating the fetal position is another crucial component of intrapartum care and management. Several studies' results have shown increased adverse outcomes when the fetus is in an occiput posterior position, including a more prolonged second stage of labor and increased cesarean delivery rate. Randomized trial results have shown that manual rotation of the fetus from an occiput posterior position to an occiput anterior position can reduce the length of the second stage of labor. Manual rotation is more effective than maternal repositioning in labor for rotating the fetal head, and it involves less technical skill and lower risk than instrumental rotation.[24]

Treatment / Management

Abnormal labor progression is associated with multiple poor maternal and fetal outcomes. Therefore, active management is crucial to prevent adverse outcomes for the mother and the baby. Most labor and delivery units have an established protocol for administering oxytocin to augment inadequate contractions. This entails administering the proper medication, dosage, and criteria for an incremental increase as clinically warranted. These protocols also include monitoring maternal and fetal status for adverse events. With a protracted or arrested second stage of labor, operative vaginal delivery with either forceps or vacuum by a skilled obstetric professional may be an option to expedite delivery. Cesarean delivery may be necessary in prolonged labor, protraction, and arrest, especially during the active phase of labor. Manual placental extraction may be required for a prolonged third stage of labor. 

Prolonged or Protracted First Stage

Latent Phase

• The latent phase can last for many hours or even days. Hence, the decision to admit the patient to the hospital depends on various factors, including the patient's cervical status, emotional state, associated complications, tolerance to pain, and physical distance from the hospital. Increased obstetrical interventions have been associated with admission during the latent phase of labor. Therefore, it is imperative to consider the options of admission versus continued outpatient management of the latent phase of labor.[25] 
• Therapeutic rest may be considered if desired. Morphine may be administered intramuscularly and intravenously simultaneously at 5 to 10 mg, with a maximum total dose of 20 mg. Alternatively, intramuscular morphine sulfate and promethazine may be used.[26]
• Oxytocin and amniotomy may be helpful in actively treating a prolonged latent phase.
• Propranolol use does not increase the chances of vaginal delivery or shorten the time to delivery in nulliparous patients with a prolonged latent phase of labor.[27]
• When both maternal and fetal conditions are stable, cesarean delivery for failed induction during the latent phase can often be avoided. Current ACOG recommendations suggest continuing oxytocin infusion for a minimum of 12 to 18 hours following membrane rupture before determining that the induction was unsuccessful. Beyond this timeframe, the decision to extend induction efforts should be guided by individual clinical factors, patient preferences, and a thorough discussion of the potential risks and benefits.[5] Most patients in the latent phase of labor, even when prolonged, will achieve a vaginal delivery with continuation of the induction.[5]
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Active Phase

• For women with a prolonged or protracted active phase of the first stage, oxytocin may be administered, and an amniotomy may be performed.
• Suppose there has been no cervical change after 4 hours of adequate uterine contractions (>200 MVUs) and ruptured membranes or 6 hours with adequate uterine contractions, ruptured membranes, and oxytocin augmentation. In that case, it is advisable to proceed with cesarean delivery.
• However, if labor progresses slowly or normally, oxytocin administration is continued.

Protracted or Arrested Second Stage

• Oxytocin augmentation is started for minimal (<1 cm) or absent descent after 60 to 90 minutes of maternal pushing with less frequent uterine contractions.
• Without epidural anesthesia, nulliparous women can push for at least 3 hours and multiparous women for at least 2 hours before considering operative intervention. As long as the fetus continues to descend and/or rotate to a favorable position for spontaneous vaginal delivery and the fetal heart rate tracing is reassuring, any operative intervention should be delayed.
• If necessary, manual rotation of the fetus from an occiput posterior presentation to an occiput anterior presentation can be attempted in a protracted second stage.
• An additional hour of pushing may be allowed in women with epidural anesthesia before considering operative intervention.
• Operative vaginal delivery may be utilized before proceeding to cesarean delivery when the second stage of labor is protracted.[5][28]
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European Guidelines for Managing Arrested or Protracted Labor in Nulliparous Women in the First Stage of Labor at Term

In 2022, an expert panel convened by the European Association of Perinatal Medicine, including obstetricians, gynecologists, midwives, and patient representatives from 9 European countries, developed evidence-based clinical guidelines for managing labor. Supported by the Knowledge Institute of the Dutch Association of Medical Specialists, the panel focused on 5 priority clinical questions concerning term, nulliparous women with a singleton fetus in cephalic presentation experiencing arrested or protracted labor due to inadequate uterine contractions. Key recommendations include considering amniotomy as an initial intervention and discussing the timing of oxytocin administration, immediate versus delayed, with patients, as current evidence does not clearly favor 1 approach.

A shared decision-making model is emphasized, incorporating clinical judgment and patient preferences. When oxytocin is indicated, a low-dose regimen is recommended for labor augmentation. Importantly, amniotomy should generally precede oxytocin infusion during the first stage of spontaneous labor. Before proceeding to operative delivery, at least 4 hours of oxytocin augmentation with adequate uterine contractions should be attempted, provided maternal and fetal conditions remain stable. These guidelines aim to promote safe, individualized, and evidence-based labor management, improving outcomes for both mothers and infants. Similarly, the WHO recommends both amniotomy and oxytocin for labor augmentation, without using amniotomy alone. In many countries, amniotomy is typically performed as the initial intervention, and if there is no noticeable progress within 1 to 2 hours, intravenous oxytocin is then initiated to support labor advancement.[29]

Differential Diagnosis

When evaluating abnormal labor, it is essential to consider a broad differential diagnosis to identify underlying causes that may impede normal progression. A structured approach to the differential diagnosis helps clinicians distinguish correctable conditions from those requiring intervention, ultimately optimizing obstetric outcomes. The differential diagnosis of abnormal labor includes the following:

• Abdominal pain
• Bandl ring
• Braxton Hicks contractions
• Cervical stenosis
• Chorioamnionitis
• Placental abruption
• Premature rupture of membranes
• Prodromal labor
• Uterine Mullerian anomaly
• Uterine rupture

Prognosis

The prognosis of abnormal labor varies according to the stage. With a prolonged first-stage latent phase of labor, intervention with amniotomy and oxytocin can be helpful and allow normal progression for the remainder of labor. These same strategies may be utilized in cases of abnormalities during the active phase of the first stage of labor. A recent randomized controlled trial of early amniotomy, within 1 hour of cervical balloon catheter expulsion, shows over 2 times faster labor than waiting longer to perform amniotomy in term patients induced with mechanical cervical ripening.[30]

Maternal and neonatal morbidity is associated with a prolonged first stage of labor, including maternal fever from endometritis, shoulder dystocia, hemorrhage, and blood transfusion.[31][32] A prolonged latent phase reaching the 90th percentile or higher in individuals who progress to active labor is linked to a higher risk of maternal complications, independent of whether a cesarean delivery occurs. An increase in third- and fourth-degree perineal lacerations, cesarean delivery, and a prolonged hospital stay is associated with a protracted or arrested second stage of labor.[32][33] 

Additionally, when a prolonged latent phase occurs during spontaneous labor, it is associated with an elevated risk of adverse neonatal outcomes.[34] The fetus has an increased risk of neonatal intensive care unit admission, low Apgar scores, and a need for assisted ventilation with abnormal labor.[33] Operative vaginal delivery may expedite the abnormal labor process in certain situations. Based on the recommended criteria, cesarean delivery is indicated with abnormal labor in the first and second stages.[35] Current methods to prevent injury, blood loss, and infection result in a good prognosis when cesarean delivery is necessitated.[24]

Complications

Roughly 20% of labor is associated with prolongation, protraction, or an arrest abnormality. Various adverse maternal and fetal outcomes are associated with labor abnormalities. Infection, operative birth, low Apgar score at 5 minutes, prolonged hospitalization for both mother and baby, third- and fourth-degree maternal perineal lacerations, above-average blood loss, and neonatal intensive care unit admission are all increased with abnormal labor progress.[36] 

With abnormal labor being the main indication for cesarean delivery during labor, the perceived safety of the cesarean delivery must be addressed. With the increasing rate of cesarean deliveries in the United States, there has been a concomitant increase in abnormal placentation, specifically placenta accreta and placenta previa, as well as cesarean scar pregnancies. Along with these complications come a parallel rise in maternal morbidity and mortality, as placenta accreta and placenta previa account for a large percentage of maternal morbidity and mortality.[37]