7.3: Normal Labor and Delivery

7.3.1 Spontaneous Labor

7.3.1.1 Initiation of Labor

The precise mechanisms that initiate spontaneous labor are not fully understood, but they are thought to involve a complex interplay of maternal, fetal, and placental signaling. Increasing uterine stretch, changes in estrogen and progesterone balance, and rising levels of prostaglandins all contribute to activation of the myometrium. These changes stimulate the release of oxytocin from the posterior pituitary and local prostaglandin production, leading to regular, rhythmic uterine contractions. Over time, contractions increase in frequency, duration, and intensity, resulting in progressive cervical dilation and effacement. 

7.3.1.2 Cervical Changes

Labor is defined as the presence of regular uterine contractions that lead to cervical dilation and effacement. In early pregnancy, the cervix is typically 4 to 5 cm in length, closed, firm, and positioned high in the pelvis. With labor, the presenting fetal part exerts pressure on the cervix, producing softening, shortening (effacement), dilation of the cervical os, and descent of the fetus (station).

On examination, the cervix is described by:

• Dilation: from closed to 10 cm
• Effacement: from 0 percent to 100 percent
• Station: the relationship of the presenting part to the ischial spines, expressed in centimeters above (negative values) or below (positive values) the spines
• Consistency: firm, medium, or soft
• Position: posterior, midposition, or anterior

Each parameter is assigned a numerical value to generate the Bishop score. A Bishop score greater than 8 is considered favorable and is associated with a likelihood of successful vaginal delivery similar to that of spontaneous labor. (Figure 7.29)

Figure 7.29: Bishop Scoring System evaluates dilation, effacement, position, consistency, and the fetal head's station in the pelvis. Each parameter is assigned points, with a total score ranging from 0 to 13. Cervical dilation, effacement, and station are scored from 0 to 3 points, whereas cervical position and consistency are scored from 0 to 2 points. 
Source: Wormer, Kelly C., Amelia Bauer and Ann E. Williford. Bishop Score. [Updated 2024 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Available from: https://www.ncbi.nlm.nih.gov/books/NBK470368/.  

7.3.1.3 Rupture of Membranes

• Prelabor Rupture of Membraes (PROM): At term, some patients experience rupture of membranes before the onset of contractions. Before 37 weeks, this is referred to as preterm prelabor rupture of membranes (PPROM) and is discussed in Pregnancy Complications: Preterm Labor and Preterm Prelabor Rupture of Membranes. After 37 weeks, most individuals enter labor within 24 hours of PROM. If spontaneous labor does not occur in a timely manner, induction or augmentation is recommended to decrease the risk of infection.
• Spontaneous Rupture of Membranes (SROM): Once labor is established, increasing intrauterine pressure from contractions commonly leads to spontaneous rupture of membranes. After SROM, contractions often become more intense and may be perceived as more painful.
• Artifical Rupture of Membranes (AROM): When SROM has not occurred or when augmentation of labor is indicated, the clinician can perform AROM using an amnihook. This procedure is typically painless and is performed during a vaginal examination by puncturing the membranes with the tip of the instrument. AROM should be performed when the fetal head is well applied to the cervix to minimize the risk of umbilical cord prolapse.

7.3.1.4 Cardinal Movements of Labor

As the fetus descends through the maternal pelvis, it undergoes a predictable series of positional changes known as the cardinal movements of labor. These movements optimize the relationship between the fetal head and the bony pelvis, facilitating vaginal birth. Although delivery can occur without each movement being clinically evident, abnormal progression may contribute to labor dystocia.64 

• Engagement: The biparietal diameter of the fetal head passes through the plane of the pelvic inlet.
• Flexion: Contact of the fetal head with the pelvic floor and soft tissues promotes flexion, bringing the chin toward the chest so that the smallest diameter (vertex) presents.
• Descent: he fetal head moves progressively downward through the pelvis.
• Internal Rotation: The fetal head initially enters the pelvis with the occiput oriented toward the maternal side, aligning the largest head diameter with the widest dimension of the pelvic inlet. With continued descent, the curvature and shape of the pelvis guide the occiput to rotate anteriorly into alignment with the maternal anteroposterior axis. Fetal position is described according to the location of the occiput. When the occiput faces the maternal abdomen the position is occiput anterior (OA); when the occiput faces the maternal back the position is occiput posterior (OP). (Figure 7.30)
• Extension: As the fetal head reaches the vulva and passes beneath the pubic symphysis, it extends along the curve of the sacrum to allow delivery of the face and chin.
• External Rotation (Restitution): After the head is delivered, it rotates back to its original orientation relative to the shoulders, which are still within the pelvis. This external rotation, or restitution, realigns the head with the shoulders.
• Expulsion: The anterior shoulder then slips under the pubic symphysis, followed by the posterior shoulder and the remainder of the body, completing the birth. (Figure 7.31 forthcoming)  

  

Figure 7.30: four possible positions in occiput presentation. 
Source: Smith, Deborah H. and Judith Rogers Fruiterman. Maternal-Infant Nursing Review. 2024. This work is distributed under a  CC BY SA 3.0. Available from https://sites.google.com/view/maternitynursingreview/home.

7.3.2 Induction of Labor

7.3.2.1 Indications

Induction of labor is performed for a wide range of maternal and fetal conditions that increase the risk of morbidity or mortality if pregnancy continues. Many of these indications have been discussed throughout this chapter, and in general, induction prior to the estimated due date is recommended when ongoing gestation poses greater risk than delivery. Historically, elective induction was believed to increase the likelihood of cesarean delivery, so it was reserved primarily for medical indications. 

 

In 2018, the ARRIVE trial significantly influenced national clinical practice. This large, multisite randomized controlled trial included nulliparous individuals at 39 weeks gestation without medical indications for induction. Participants were randomized to elective induction at 39 weeks or expectant management until at least 40 weeks and 5 days or earlier if a medical indication arose, such as preeclampsia. The trial demonstrated no increase in cesarean section rates in the induction group. In fact, the induction group had a lower cesarean delivery rate, likely due to reduced fetal intolerance of labor associated with healthier placental function at 39 weeks. The induction group also showed lower rates of gestational hypertension and preeclampsia, with no significant differences in perinatal outcomes. 65 As a result, elective induction at 39 weeks has become a common and evidence-supported option for low-risk patients who desire it. 66

 

7.3.2.2 Methods

Induction of labor may be achieved through pharmacologic, mechanical, or physiologic methods. Most approaches target prostaglandin pathways or oxytocin release to promote cervical ripening and stimulate contractions.

Natural Oxytocin Release

• Nipple stimulation: Manual stimulation or use of a breast pump promotes endogenous oxytocin release, which can increase uterine activity.
• Membrane sweeping: During a cervical examination, the clinician sweeps a finger circumferentially through the internal os. (Figure 7.31 forthcoming). (INSERT IMAGE). This separates the amniotic membranes from the lower uterine segment and triggers local prostaglandin production.
• Sexual intercourse: Semen contains prostaglandins, contributing to cervical softening. Orgasm also stimulates endogenous oxytocin release, which may initiate contractions.

Prostaglandins

If spontaneous methods are insufficient, synthetic prostaglandins can be administered for cervical ripening, particularly when the Bishop score is low, as described in Cervical Changes.

• Prostaglandin E1 (Misoproostol, Cytotec): Administered vaginally or orally, misoprostol softens the cervix and stimulates contractions. Although FDA approved for peptic ulcer disease, it is widely used off label in obstetrics. Side effects include tachysystole, which may lead to fetal intolerance of labor.
• Prostaglandin E2 (Dinoprostone, Cervidil): A vaginal insert placed on a string, dinoprostone functions similarly to misoprostol but is more expensive. It is FDA approved for cervical ripening and is associated with lower rates of tachysystole. Because the insert can be removed if complications arise, it offers a safety advantage in cases of uterine hyperstimulation or fetal distress.

 

Mechanical Ripening

Mechanical dilation is an alternative for individuals in whom prostaglandins are contraindicated, such as those attempting a trial of labor after cesarean (TOLAC). Mechanical methods may also be combined with prostaglandins to enhance cervical ripening.

• Foley balloon: A standard Foley catheter is inserted through the cervix, and the balloon is inflated above the internal os. Downward tension helps dilate the cervix as the balloon descends. Cervical dilation of approximately 3 cm is commonly achieved.
• Cook catheter: This dual-balloon catheter dilates the cervix from both above and below, allowing greater fluid volume and producing more extensive dilation compared with the single-balloon method.

Pitocin

Synthetic oxytocin (Pitocin) is administered intravenously in a titrated fashion to generate rhythmic contractions. Pitocin is most effective when the cervix is already favorable. If the Bishop score is less than 9, cervical ripening is often recommended prior to initiating oxytocin. 

7.3.3 Monitoring

7.3.3.1 Fetal Heart Rate Tracings

Source for this section content:

ACOG. Intrapartum Fetal Heart Rate Monitoring: Interpretation and Management. Clinical Practice Guideline, No. 10 (October 2025). Restricted access, https://www.acog.org/clinical/clinic...and-management.⁶⁶

As described in Routine Prenatal Care: Antenatal Testing, continuous fetal cardiotocographic monitoring provides real-time assessment of fetal well-being. Interpretation of fetal heart rate (FHR) patterns is essential in identifying fetuses at risk for hypoxemia or acidemia. Standardized criteria have been established to guide clinical management.

Components

• Baseline heart rate: The normal FHR baseline ranges from 110 to 160 beats per minute (bpm). A baseline above 160 bpm constitutes tachycardia, and a baseline below 110 bpm constitutes bradycardia.
• Variability: Variability refers to the fluctuations in FHR from minute to minute.
  • Moderate variability (6–25 bpm) indicates adequate oxygenation and an intact autonomic nervous system and is considered reassuring.
  • Minimal variability (≤ 5 bpm) may reflect fetal hypoxia, sleep cycles, or medication effects.
  • Absent variability is strongly associated with fetal compromise.
  • Marked variability (> 25 bpm) is of uncertain significance.
• Accelerations: Accelerations are transient increases in FHR of at least 15 bpm lasting at least 15 seconds. Their presence reliably predicts fetal well-being, although absence of accelerations alone does not indicate distress, as fetal sleep cycles may diminish their frequency.
• Decelerations: Decelerations are transient decreases in FHR below the baseline.
  • Early decelerations: These gradual decreases mirror uterine contractions and are caused by fetal head compression. They are benign. (Figure 7.32)
  • Late decelerations: These gradual decreases begin after the onset of a contraction and recover after its completion. They reflect uteroplacental insufficiency and may indicate fetal hypoxia. (Figure 7.33)
  • Variable decelerations: These abrupt decreases of at least 15 bpm lasting 15 seconds to 2 minutes are caused by umbilical cord compression. They may occur with or without contractions. Repetitive variable decelerations can compromise fetal oxygenation. (Figure 7.34)
  • Prolonged decelerations: FHR decreases lasting between 2 and 10 minutes are considered prolonged decelerations. These are always concerning and require immediate evaluation. (Figure 7.35)

Figure 7.32: Early Decelerations are visually apparent, gradual (onset to lowest point ≥30 seconds) decrease in and return to baseline FHR associated with UCs. They are thought to be caused by transient fetal head compression and are considered a normal and benign finding. 
Source: Smith, Deborah H. and Judith Rogers Fruiterman. Maternal-Infant Nursing Review. 2024. This work is distributed under a  CC BY SA 3.0. Available from https://sites.google.com/view/maternitynursingreview/home.

Figure 7.33: Latge Decerlations - visually apparent, gradual (onset to lowest point >30 seconds) decrease in and return to baseline FHR associated with UCs. 
Source: Smith, Deborah H. and Judith Rogers Fruiterman. Maternal-Infant Nursing Review. 2024. This work is distributed under a  CC BY SA 3.0. Available from https://sites.google.com/view/maternitynursingreview/home.

Figure 7.34: Variable Decelerations - visually abrupt (onset to lowest point less than 30 seconds) and apparent decrease in FHR below the baseline. 
Source: Smith, Deborah H. and Judith Rogers Fruiterman. Maternal-Infant Nursing Review. 2024. This work is distributed under a  CC BY SA 3.0. Available from https://sites.google.com/view/maternitynursingreview/home.

Figure 7.35: Prolonged Decelerations - visually apparent decrease (may be either gradual or abrupt) in FHR of at least 15 bpm below the baseline and lasting more than two minutes but less than 10 minutes. 
Source: Smith, Deborah H. and Judith Rogers Fruiterman. Maternal-Infant Nursing Review. 2024. This work is distributed under a  CC BY SA 3.0. Available from https://sites.google.com/view/maternitynursingreview/home.

Categories of Fetal Heart Rate Patterns

Categorization systems have been developed to assist in evaluating fetal status and identifying when intervention is necessary.

• Category I: Normal baseline (110–160 bpm), moderate variability, presence or absence of accelerations, and no decelerations other than early decelerations. This pattern is reassuring and indicates normal fetal acid-base status. (Figure 7.36 forthcoming)
• Category II: Any tracing that does not meet criteria for Category I or Category III. This is an indeterminate category that encompasses a wide range of patterns. Management depends on clinical context, gestational age, and the clinician’s expertise. (Figure 7.37 Forthcoming)
• Category III: Absent variability with recurrent late decelerations, recurrent variable decelerations, or bradycardia, or a sinusoidal pattern (Figure 7.38 forthcoming) (INSERT IMAGE OF SINUSOIDAL PATTERN). Category III tracings signify a high likelihood of fetal acidemia and warrant prompt evaluation and rapid corrective measures. If the tracing does not improve, expedited delivery is recommended. (Figure 7.39 forthcoming)

7.3.3.2 Contraction Monitoring

Methods

• Tocodynamometer: An external pressure-sensitive device placed over the uterine fundus detects changes in tone during contractions. It reliably identifies contraction frequency but does not accurately assess contraction strength. (Figure 7.42 forthcoming)
• Intrauterine pressure catheter (IUPC): When precise measurement of contraction strength is needed, an IUPC can be placed after membrane rupture. It records intrauterine pressure in Montevideo units and assists in determining adequacy of contractions. The catheter also contains a channel that permits amnioinfusion, which may be used to relieve umbilical cord compression in cases of recurrent variable decelerations. (Figure 7.43 forthcoming)

7.3.4 Pain Control

7.3.4.1 Pain Relief During Labor

Source for this section content:

ACOG. Obstetric Analgesic and Aneshtesia. Practice Bulleting, No. 209 (March 2019). Restricted access, https://www.acog.org/clinical/clinic...and-anesthesia.⁶⁷

Effective pain management is an essential component of intrapartum care. Multiple modalities exist, ranging from nonpharmacologic strategies to regional and general anesthesia. Selection depends on patient preference, clinical circumstances, and institutional resources.

Position Changes, Massage, and Supportive Care

Nonpharmacologic methods such as maternal repositioning, massage, hydrotherapy, and focused breathing techniques can reduce labor discomfort and improve coping.

• Doulas: Continuous labor support from a trained support person has been associated with improved maternal outcomes, including decreased use of analgesia, lower intervention rates, and increased satisfaction with the birth experience. Evidence from randomized controlled trials demonstrates that one-on-one support decreases the need for intrapartum analgesia.⁶⁸ 

Intravenous and Intramuscular Medications

Opioid analgesics such as morphine, fentanyl, butorphanol, or nalbuphine may provide temporary relief from labor pain. These agents can reduce the perception of discomfort, though they are often insufficient for managing the intensity of active labor contraction pain. Because opioids cross the placenta, use near delivery can result in neonatal respiratory depression. Careful timing and dosing are therefore required.

Nitrous Oxide

Self-administered nitrous oxide, commonly known as “laughing gas,” offers a noninvasive method of analgesia. It provides partial pain relief and anxiolysis and can be used intermittently during contractions. Nitrous oxide is less effective than epidural analgesia but may be preferred by patients seeking mobility or avoiding invasive procedures.

Epidural Analgesia

Epidural anesthesia is the most effective and commonly used method for pain relief during labor. A catheter is placed in the epidural space, typically at the L3-L4 or L4-L5 interspace, allowing continuous infusion of anesthetic agents. These medications block neural transmission from the uterus (T10-L1) and vagina and perineum (S2-S4), providing substantial pain relief with minimal neonatal effects.69  (Figure 7.45 forthcoming)

 

 

Spinal Analgesia

A single injection of anesthetic into the subarachnoid space can produce rapid and profound analgesia. Spinal anesthesia is used infrequently for labor analgesia because of its shorter duration but is commonly used for cesarean delivery when a rapid onset of surgical anesthesia is needed. It may also be combined with an epidural catheter in a combined spinal-epidural approach.

Pudendal Block

The pudendal nerve provides sensory innervation to the lower vagina and perineum. A pudendal nerve block involves injecting local anesthetic transvaginally near the ischial spine. While it does not relieve contraction pain, it is effective for reducing discomfort associated with second-stage pushing, operative vaginal deliveries, and perineal repair.(Figure 7.46 forthcoming)

Local Anesthesia

Local infiltration of anesthetic agents such as lidocaine or bupivacaine into the perineal tissues can be performed after delivery to facilitate repair of lacerations or episiotomies.

General Anesthesia

General anesthesia may be required in select circumstances, including:

• Emergent cesarean delivery when no functional epidural or spinal anesthesia is in place
• Contraindications to regional anesthesia
• Failure or inadequacy of regional anesthesia

While general anesthesia is generally safe in pregnancy, regional techniques remain the preferred approach for cesarean delivery because they are associated with lower maternal and fetal risks. 

7.3.5 Stages of Labor

7.3.5.1 First Stage

The first stage of labor is defined as the interval from the onset of regular, painful uterine contractions to complete cervical dilation at 10 cm. This stage is subdivided into two phases:

• Latent phase: The latent phase begins with the onset of regular contractions and continues until the cervix reaches 6 cm dilation. Considerable variability exists in the duration of the latent phase, and it may progress over several hours to weeks.
• Active phase: The active phase spans from 6 cm to complete dilation at 10 cm. This phase is characterized by more rapid cervical change. Multiparous patients generally have shorter active phases compared to nulliparous individuals.

7.3.5.2 Second Stage

The second stage begins once full dilation (10 cm) is achieved and continues until the delivery of the neonate. During this stage, the patient engages in voluntary pushing efforts coordinated with contractions. Duration varies by parity and anesthesia use. A second stage lasting up to 4 hours can be normal under certain circumstances. Prolonged duration beyond these thresholds is considered labor dystocia and warrants clinical evaluation and management.

7.3.5.3 Third Stage

The third stage of labor encompasses delivery of the placenta. After the neonate is delivered, the placenta typically separates and delivers spontaneously within 30 minutes. Active management of the third stage is advised to reduce the risk of postpartum hemorrhage and includes administration of intravenous or intramuscular Pitocin along with controlled umbilical cord traction.

7.3.6 Lacerations

Source for this section content:

ACOG. Prevention and Management of Obstetric Lacerations at Vaginal Delivery. Practice Bulleting, No. 198 (Sept. 2018). Restricted access, https://www.acog.org/clinical/clinic...ginal-delivery.⁷⁰

Episiotomy, a surgical incision of the perineum intended to enlarge the vaginal outlet, was historically performed frequently but is now used more selectively, as routine episiotomy has not demonstrated maternal benefit. Spontaneous lacerations, however, are common, particularly in nulliparous patients. Severe lacerations involving the anal sphincter complex can result in long-term pelvic floor dysfunction, including fecal incontinence, underscoring the importance of meticulous prevention and repair.

7.3.6.1 Degrees of Perineal Lacerations 

The perineal body, composed of the transverse perineal muscles and attachments of the bulbocavernosus muscle, is the most common site of obstetric laceration. The anal sphincter complex lies just inferior to the perineal body (Figure 7.47 forth coming)

Lacerations are classified by depth and structures involved: 

• First degree: Injury limited to the perineal skin
• Second degree: Involvement of skin and underlying perineal muscles without extension into the anal sphincter
• Third degree: Partial or complete disruption of the anal sphincter complex
• Fourth degree: Extension through the anal sphincter into the rectal epithelium. (Figure 7.48 forthcoming)

7.3.6.2 Risk Factors

Factors associated with more extensive perineal trauma include nulliparity, operative vaginal delivery, fetal macrosomia, and midline episiotomy.

7.3.6.3 Prevention

Strategies to reduce the incidence or severity of lacerations include prenatal and intrapartum perineal massage, warm compresses applied during the second stage of labor, and maternal positioning techniques that optimize perineal relaxation.

7.3.7 Neonate

7.3.7.1 Physiologic Changes Upon Delivery

Lungs

In utero, fetal lungs are fluid-filled, and surfactant production facilitates alveolar stability in preparation for extrauterine life. At birth, the neonate transitions from placental gas exchange to pulmonary respiration. The first breaths generate negative intrathoracic pressure, drawing air into the lungs and displacing alveolar fluid into the interstitium for absorption. Surfactant reduces surface tension and prevents alveolar collapse during this transition.

Cardiovascular

As the lungs expand and oxygenation increases, pulmonary vascular resistance rapidly decreases. This leads to increased pulmonary blood flow and functional closure of the ductus arteriosus. After umbilical cord clamping, systemic vascular resistance increases while venous return from the placenta ceases, reducing left ventricular preload and contributing to the postnatal cardiovascular shift.

Skin-to-skin contact

Immediate skin-to-skin contact after birth has demonstrated multiple maternal and neonatal benefits. These include improved thermoregulation, enhanced breastfeeding initiation and continuation, stabilization of neonatal glucose levels, and reduced maternal postpartum hemorrhage due to increased endogenous oxytocin release.⁷¹

7.3.7.2 Delayed Cord Clamping

Delayed umbilical cord clamping—waiting at least 30 to 60 seconds before clamping—is recommended for vigorous term and preterm neonates. Benefits include higher neonatal hemoglobin levels at birth and increased iron stores during infancy. In preterm infants, delayed clamping is associated with reduced rates of intraventricular hemorrhage, necrotizing enterocolitis, and improved overall survival.⁷²

7.3.7.3 APGAR Evaluation

Source for the section content:

ACOG. 

Immediately after delivery, the neonate is assessed using the APGAR score, which evaluates five parameters:

• Appearance: skin color
• Pulse: heart rate
• Grimace: reflex irritability
• Activity: muscle tone
• Respiration: respiratory effort

Each category receives a score from 0 to 2, for a maximum score of 10. Assessments occur at 1 minute and 5 minutes after birth. A score of 7 or greater is reassuring. If the initial score is less than 7, the evaluation is repeated every 5 minutes for up to 20 minutes. (Figure 7.49 forthcoming)  Although helpful for assessing the need for acute resuscitative interventions, the APGAR score has limitations and does not reliably predict long-term neurologic outcomes.

7.3.7.4 Umbilical Cord Gases

Following cord clamping, a segment of the umbilical cord may be collected to sample arterial and venous blood gases. Cord gases provide objective data regarding the neonate’s acid-base status at birth and can help identify perinatal hypoxia or acidosis, thereby informing immediate neonatal management.