Stages of Labor

Overview of Stages of Labor

• Labor is the process during which coordinated uterine contractions lead to the delivery of an infant. This normal physiological process consists of three stages (Table 1).¹
  • The first stage is characterized by the onset of regular uterine contractions, which increase in frequency and strength, leading to cervical effacement and dilation to 10 centimeters (cm).¹
  • The second stage begins after full cervical dilation is reached and ends with the delivery of the neonate.¹
  • The third stage refers to the period between the birth of the neonate and the delivery of the placenta and fetal membranes.¹
• The progression of labor is influenced by the relationship between three key factors: maternal efforts and anatomy, uterine contractions, and fetal characteristics, including size and presentation. Various clinical interventions, such as neuraxial analgesia, can be utilized throughout the labor process.¹
• The labor and delivery plan can be influenced and altered due to labor dysfunction. Anesthesia providers’ recognition of labor dysfunction is crucial in developing an anesthetic plan that meets the needs of various delivery methods.
• There is no specific cervical dilation threshold required for neuraxial placement during labor. Neuraxial anesthesia can be provided during any phase of labor.²
• Disorders of labor protraction and arrest, as well as prolonged pushing, increase the risk of hemorrhage.²

Stage 1: Dilation

The first stage of labor begins with the onset of labor through complete cervical dilation (10 cm). It is divided into two phases: latent (or early) and active labor.^1-3

Latent Phase of Labor^2,3

• Latent labor commences with labor onset with regular uterine contractions and lasted until 6 cm of cervical dilation is achieved.
• Typically, cervical dilation is gradual.

Active Phase of Labor^2,3

• The active phase of labor begins at a cervical dilation of 6 cm and lasts until complete cervical dilation at 10 cm.
• During this phase, cervical dilation can be rapid.

Abnormal Labor Progression^2,3

• Abnormal labor progression manifests in the active phase as labor arrest or protraction.
• Labor arrest refers to the cessation of labor progression. Protraction of labor refers to the slow progression of labor.
  • Labor arrest during the active phase occurs when the patient is at least 6 cm dilated with rupture of membranes, and no cervical dilation occurs in the setting of 4 hours of adequate uterine activity or 6 hours of inadequate uterine activity with oxytocin augmentation.²
  • Protraction of labor occurs in a parturient who is at least 6 cm dilated and who dilates less than 1 – 2 cm in 2 hours.
• Risk factors include nulliparity, maternal obesity, older maternal age, non-occiput anterior position, large for gestational age, macrosomia, and cephalopelvic disproportion.^2,3
• An active approach to managing the first stage of labor is preferred over expectant management, and various strategies are utilized in cases of abnormal labor progression, including amniotomy, oxytocin augmentation, and maternal repositioning or mobilization.²
• Labor dystocia at this stage increases the likelihood of cesarean delivery, and anesthesia teams should anticipate the need for operative management.²
• Prolonged labor can lead to maternal physical and emotional exhaustion. Operative vaginal assisted delivery may be required.² The labor epidural can be dosed appropriately for maternal comfort during this process, as well as converted to neuraxial anesthesia in the event of a cesarean delivery.
• Additionally, prolonged labor can lead to increased epidural top-ups. Additional medication administration through the epidural carries a risk of hypotension, which should be treated immediately.

Stage 2: Pushing and Delivery

The second stage of labor begins at a cervical dilation of 10 cm and ends with the delivery of the neonate.^1,2

• During this phase, a variety of pushing techniques can be utilized, including the traditional technique of using a Valsalva with a closed glottis during contractions or “spontaneous” pushing, where the parturient bears down without holding her breath and with an open glottis.⁴

Abnormal Labor Progression

• Abnormal labor progression can occur during the second stage of labor, either as prolonged labor or descent disorders.^4,5
  • Prolonged second stage of labor
    • A prolonged second stage of labor occurs when there is more than 3 hours of pushing in nulliparous parturients and 2 hours of pushing in multiparous parturients occurs.^2,5
    • Risks of a prolonged second stage include maternal infection, postpartum hemorrhage, NICU admission, and neonatal sepsis. If a cesarean section is required, the fetal head may be trapped in the pelvis, which can make extraction difficult and cause thinning of the lower uterine segment, increasing the risk of hysterotomy extensions.⁵
  • Disorders of descent include failure of descent, arrest of descent, and protracted descent.⁴
    • Failure of descent occurs when there is no descent from the onset of the active phase to the deceleration phase or full dilation of the cervix.
    • Arrest of descent is when active descent stops for 1 hour or more.
    • Protracted descent occurs when the active descent rate slows (< 1 cm per hour in nulliparous parturients and < 2 cm per hour in multiparous parturients).
• Prolongation of the second stage, often accompanied by maternal exhaustion or mechanical factors limiting descent, may necessitate operative delivery of the neonate, either through forceps- or vacuum-assisted vaginal delivery, or cesarean delivery. Anesthesia providers should anticipate the possibility of instrumental delivery to ensure that adequate analgesia is provided while also remaining prepared to convert to anesthesia suitable for cesarean delivery if necessary.⁶

Stage 3: Placental Delivery

The third stage of labor occurs between the delivery of the neonate and the delivery of the placenta.^1,2

• During this stage, the classic signs of placental separation include the lengthening of the umbilical cord, a gush of blood from the vagina, and an increased firmness and globular shape of the uterine fundus.^1,7
• This stage can be managed actively with interventions like uterotonic agents, controlled cord traction, uterine massage, and sometimes manual extraction, or expectantly, where interventions are not initially used.⁷

Abnormal Labor Progression

• Abnormal progression during the third stage of labor can occur due to uterine atony and placental complications. The risk of postpartum hemorrhage (PPH) is increased in both cases. Uterine atony is the most common cause of PPH.^7,8
  • Placental complications^7,8
    • Placenta accreta spectrum disorders involve abnormal adherence and invasion of the placenta into the uterine wall, resulting in a lack of spontaneous separation during this phase.
    • Trapped placenta involves complete placental detachment but a failure to expel due to closure of the cervix.
• Risk factors for uterine atony include uterine distention, distortion of the uterine cavity, prolonged oxytocin exposure, chorioamnionitis, and general anesthesia. Meanwhile, placental abnormalities are more common in cases of preterm births, a history of previous cesarean deliveries, and uterine anomalies, among other factors.^7,8
• Collaboration between anesthesia and obstetric providers is important in active management of the third stage of labor by reducing maternal morbidity and mortality through postpartum hemorrhage prevention and response, maternal hemodynamic support, and analgesic management.^7,8

Analgesia for Labor and Regional Techniques

Neuraxial analgesia is the gold standard for labor pain. Recent randomized controlled trials have shown that the timing of analgesia initiation does not adversely affect labor progression.⁹ A patient’s request for labor analgesia is sufficient justification for epidural placement in the setting of no other medical contraindications.⁹

• Neuraxial anesthesia should be offered for labor analgesia at any stage of labor and at any cervical dilation.^2,8
  • The incidence of cesarean delivery is not increased with neuraxial analgesia.⁸
  • Options of neuraxial analgesia include epidural, dural puncture epidural, combined spinal epidural, and spinal when delivery is imminent.8,10
  • Extended duration of labor can lead to the need for additional epidural top-ups to maintain adequate analgesia, which can increase the risk of failed conversion to surgical anesthesia if cesarean delivery becomes necessary.⁶
• Regional blocks, including paracervical, paravertebral lumbar sympathetic, and/or pudendal nerve block, can be used during different stages of labor (Table 2).
  • Paracervical blocks can be used in the first stage of labor to aid in pain relief from cervical dilation. Fetal bradycardia is a major risk factor likely due to uterine artery constriction or increased uterine tone.¹⁰
  • Paravertebral lumbar sympathetic blocks can be used to block pain transmission from the cervical and uterine areas during the first stage of labor. Risks include intravascular injection, technical difficulty, and maternal hypotension.¹⁰
  • Pudendal nerve blocks can be used in the second stage of labor to block sacral nerve roots, S2 to S4; however, the reliability can be questionable. It can be beneficial for episiotomy repair.¹⁰