What are the stages of labor in a low-risk pregnancy?

Stages of Labor

Labor is divided into three distinct stages: the first stage (subdivided into latent and active phases), the second stage (from complete cervical dilation to delivery), and the third stage (from delivery to placental expulsion). 1

First Stage of Labor

The first stage consists of two phases that are distinguished by the rate of cervical dilation rather than by specific centimeter measurements 2.

Latent Phase

• Begins with the onset of regular uterine contractions and continues until cervical dilation accelerates 2
• Characterized by a relatively flat slope of cervical dilation 2
• Can occur at various degrees of cervical dilation—there is no fixed centimeter threshold 2
• Serial vaginal examinations at least every 2 hours are essential to identify when the dilation rate transitions from latent to active phase 2, 1

Active Phase

• Begins when the rate of cervical dilation transitions from the flat slope of latent phase to a more rapid slope, regardless of the specific degree of dilation achieved 2
• No diagnostic manifestations demarcate its onset other than accelerating dilation 2
• Normal dilation rates are ≥1.2 cm/hour for nulliparous women and ≥1.5 cm/hour for multiparous women 2, 1
• The WHO has used a rounded lower limit of 1.0 cm/hour for convenience 2
• Mean duration is approximately 7.7 hours for nulliparas and 5.6 hours for multiparas (with statistical limits of 17.5 and 13.8 hours respectively) 3
• Ends with a deceleration phase, which is usually short and frequently undetected 2

Common Pitfall: Uterine contraction assessment (palpation or Montevideo Units) is of limited value in determining active phase onset because contractions inconsistently increase in intensity, frequency, and duration—only the dilation pattern is reliable 2.

Abnormal First Stage Patterns

Several aberrant labor patterns can occur during the active phase 2:

• Protracted dilation (slower than normal rates) 2
• Arrest of dilation 2
• Prolonged deceleration phase (>2-3 hours in nulliparas, >1 hour in multiparas) 2
• Failure of descent 2

Risk factors include: cephalopelvic disproportion, excessive neuraxial block, poor uterine contractility, fetal malpositions or malpresentations, uterine infection, maternal obesity, advanced maternal age, and previous cesarean delivery 2, 1.

Critical Warning: A prolonged deceleration phase is strongly associated with cephalopelvic disproportion, second stage abnormalities, and shoulder dystocia if vaginal delivery occurs 2.

Second Stage of Labor

The second stage begins at complete cervical dilation (10 cm) and ends with delivery of the fetus 1, 4.

Duration

• The WHO recommends allowing 2-3 hours for the second stage 1, 4
• Mean duration is 54 minutes for nulliparas (statistical limit 146 minutes) and 18 minutes for multiparas (statistical limit 64 minutes) 3
• Median duration ranges from 14-66 minutes in nulliparous women and 6-12 minutes in parous women (95th percentiles: 65-138 minutes and 58-76 minutes respectively) 5
• Some women may labor longer than traditionally expected and still achieve vaginal birth without adverse perinatal outcomes 5

Management

• The mother should receive emotional support and encouragement to bear down instinctively when she feels the urge, in the position she feels enables her to push most effectively—but not the supine position 4
• Avoiding prolonged bearing down efforts is recommended to prevent complications 1
• The baby's heart rate should be monitored after every second contraction 4
• Consider assisted vaginal delivery (forceps or vacuum) if spontaneous delivery cannot be achieved rapidly 1, 4
• Uterine fundal pressure has not been shown to be effective and may be dangerous 4

Critical Consideration: The second stage constitutes the time of greatest risk for the baby, requiring birth attendants to have skills to overcome difficulties such as poor progress, shoulder dystocia, and breech birth 4.

Third Stage of Labor

The third stage begins with delivery of the fetus and ends with expulsion of the placenta 1.

Duration and Management

• Normal duration is up to 1 hour if not actively managed 1
• Management focuses on preventing postpartum hemorrhage 1
• Ergometrine is contraindicated during the third stage 1

Risks of Prolonged Labor

Extending the first and/or second stage of labor carries specific risks 6:

• Postpartum hemorrhage 6
• Intraamniotic infection 6
• Potentially increased neonatal adverse outcomes 6

Management of labor disorders consists of: oxytocin administration, amniotomy, intrauterine pressure catheter use, and shared decision-making regarding expectant management, operative vaginal delivery, or cesarean delivery after weighing risks and benefits 6.