Prolonged labor, also known as dystocia or “failure to progress,” refers to the labor process extending beyond an expected duration. When the progression of labor slows or stops, careful medical assessment is required to ensure the safety of both the mother and the baby. This condition is a leading reason for primary Cesarean deliveries, making its definition, causes, and management a central focus of modern obstetric care.
Defining Prolonged Labor by Stage
Clinical definitions of prolonged labor use specific time thresholds across the three main stages of the process. The first stage is split into a latent phase and an active phase. The latent phase is considered prolonged if it lasts longer than 20 hours for a first-time mother (nulliparous) or more than 14 hours for a mother who has delivered before (multiparous).
The active phase begins when the cervix reaches 6 centimeters of dilation and is defined by the rate of cervical change. Protracted active labor is diagnosed if the cervix dilates at a rate of less than 1 centimeter per hour. A complete arrest of labor is diagnosed in a patient at 6 centimeters or more of dilation who has had no cervical change despite four hours of adequate uterine contractions, or six hours when using oxytocin augmentation.
The second stage of labor begins when the cervix is fully dilated and lasts until the baby is born. This stage is considered prolonged if it exceeds three hours in a first-time mother or two hours in a mother who has delivered before. These time limits are often extended by one hour if the mother has received epidural anesthesia, provided both mother and fetus remain stable.
Key Causes of Labor Prolongation
Labor may slow or fail to progress due to issues categorized into the three “Ps”: the Power, the Passenger, and the Passage.
Power
Issues with the Power refer to the effectiveness of the uterine contractions. Contractions may be too weak, infrequent, or uncoordinated to dilate the cervix or push the baby down. This muscular fatigue, or uterine inertia, can result from the uterus becoming metabolically exhausted from a long labor.
Passenger
Problems with the Passenger relate to the baby’s size or position, which impedes descent through the birth canal. Fetal malposition is a common issue, such as a persistent occiput posterior presentation, where the back of the baby’s head faces the mother’s spine instead of her abdomen. The baby may also be disproportionately large, a condition known as fetal macrosomia, which creates an obstacle to delivery.
Passage
The Passage involves the size and shape of the mother’s pelvis or soft tissues, which can physically obstruct the baby’s progress. While absolute cephalopelvic disproportion (CPD), where the pelvis is too small for any baby, is rare, a relative CPD can occur when the baby’s head cannot navigate the maternal pelvis due to position or size.
Risks for Mother and Baby
The extended duration of labor creates specific health risks for both the mother and the infant.
Maternal Risks
For the mother, primary concerns include infection and excessive blood loss. Prolonged labor, especially after the membranes have ruptured, significantly increases the risk of chorioamnionitis, a bacterial infection of the amniotic fluid and membranes. This infection can diminish the uterus’s contractile force, leading to postpartum hemorrhage (PPH). PPH is often caused by uterine atony, the failure of the uterus to contract and compress blood vessels after the placenta detaches. Prolonged, obstructed labor also increases the risk of uterine rupture, particularly in mothers with a prior Cesarean delivery scar.
Fetal Risks
For the baby, prolonged labor is associated with fetal distress, indicated by abnormal heart rate patterns that signal insufficient oxygen. This can lead to perinatal asphyxia, which is oxygen deprivation that may result in neurological injury. Babies born following prolonged labor have an increased risk of neonatal sepsis from the ascending maternal infection and are more likely to require admission to the Neonatal Intensive Care Unit (NICU).
Interventions and Management Strategies
The management of prolonged labor is dictated by the underlying cause and the stage of labor. If the issue is insufficient Power, the medical team initiates labor augmentation to strengthen contractions. This frequently involves intravenous oxytocin, a synthetic hormone that stimulates the uterus.
Oxytocin is delivered through a controlled infusion pump, with the dosage gradually increased until contractions reach an adequate pattern, typically three to five contractions in a 10-minute window. Artificial rupture of the membranes (amniotomy) is often performed alongside oxytocin to enhance contraction effectiveness.
If augmentation fails, or if the cause is a physical obstruction from the Passenger or Passage, operative delivery becomes necessary. The choice between an assisted vaginal delivery (using a vacuum device or forceps) and a Cesarean section depends on the baby’s position and descent. A Cesarean section is often the safest course of action when there is clear evidence of disproportion or a high risk of birth trauma.