Medical School · Year 2 · Reproductive · includes a quiz and discussion video

Lecture 8: Labor and Delivery

Unit 2.4: Reproductive System

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the stages of labor and their management
2. Explain the mechanisms of labor and fetal positions
3. Describe the indications for labor induction and methods
4. Explain the indications for cesarean delivery
5. Describe intrapartum fetal monitoring
6. Explain common labor complications and their management

Section 1: Initiation and Physiology of Labor

Labor represents the culmination of pregnancy, a complex physiologic process involving coordinated uterine contractions, cervical change, and fetal expulsion. The precise triggers initiating labor remain incompletely understood, though both maternal and fetal signals contribute to this carefully timed event.

The hormonal milieu shifts dramatically as labor approaches. Rather than an absolute decline in progesterone (which remains elevated until delivery), a functional progesterone withdrawal occurs through changes in receptor expression and local metabolism. Estrogen levels rise relative to progesterone, increasing oxytocin receptor expression and gap junction formation between myometrial cells, enabling synchronized contractions. Prostaglandins, produced locally in the cervix and membranes, promote both cervical ripening and uterine contractility. Oxytocin, released from the posterior pituitary, stimulates myometrial contractions, and the sensitivity to oxytocin increases markedly near term. Fetal contributions include cortisol from the maturing fetal adrenal gland, which stimulates placental enzymes altering steroid production, and surfactant components from mature fetal lungs that may signal readiness for extrauterine life.

The cervix must undergo extensive remodeling before labor can progress. Cervical ripening involves breakdown of collagen cross-links, increased hyaluronic acid content, and increased water content, transforming the cervix from a firm, closed structure to one that is soft and distensible. Effacement describes the thinning and shortening of the cervix, measured as a percentage (0% means full length, 100% is paper-thin) or in centimeters. Dilation refers to the opening of the cervical os, measured from 0 to 10 cm, with 10 cm representing complete dilation sufficient for passage of the fetal head.

The Bishop score provides a standardized assessment of cervical readiness for labor, combining dilation (0-3 points), effacement (0-3 points), station (0-3 points), cervical consistency (0-2 points), and cervical position (0-2 points). A score of 8 or higher indicates a favorable cervix likely to respond to induction, while a score below 6 typically requires cervical ripening before oxytocin administration.

<image>Panel A: Hormonal changes preceding labor including functional progesterone withdrawal through decreased receptor expression, increasing estrogen-to-progesterone ratio, oxytocin receptor upregulation on myometrial cells, and fetal cortisol production from the adrenal gland. Panel B: Cervical changes shown in cross-sectional views including progressive ripening with collagen breakdown, effacement (shortening from 100% to 0%), and dilation (opening from closed to 10 cm). Panel C: Bishop score grid with scoring criteria for dilation, effacement, station, consistency, and position, with interpretation showing less than 6 as unfavorable needing ripening and 8 or greater as favorable for induction. Panel D: Myometrial preparation showing gap junction formation between cells enabling synchronized contractions, prostaglandin production in cervix and membranes, and increased myometrial sensitivity to oxytocin near term.</image>

Section 2: Stages of Labor

Labor is divided into four distinct stages, each with characteristic features and management considerations.

The first stage of labor extends from the onset of regular contractions with cervical change to complete cervical dilation (10 cm). This stage is further subdivided. The latent phase encompasses cervical dilation from 0 to 6 cm, characterized by irregular contractions of variable intensity and slow, often unpredictable progress. Duration is highly variable, particularly for nulliparous women, and may last 20 hours or more. The active phase spans 6 to 10 cm dilation, marked by regular, more intense contractions occurring every 2-3 minutes and more predictable progress (historically defined as at least 1 cm/hour, though recent data suggest slower progress may be normal, particularly in nulliparous women). Total first stage duration averages 12-18 hours for nulliparous women and 6-10 hours for multiparous women.

The second stage begins at complete cervical dilation and ends with delivery of the infant. During this stage, the mother experiences an urge to push as the presenting part descends through the birth canal. Pushing efforts, combined with uterine contractions, expel the fetus. Duration varies with parity and presence of epidural analgesia: up to 3 hours is allowed for nulliparous women with epidural, up to 2 hours for multiparous women with epidural, with somewhat shorter times without epidural.

The third stage extends from delivery of the infant to expulsion of the placenta. This typically occurs within 30 minutes. Signs of placental separation include a gush of blood, lengthening of the umbilical cord, and the uterus becoming firm and globular. Active management of the third stage, involving prophylactic uterotonic administration (typically oxytocin after delivery of the anterior shoulder or immediately after delivery), early cord clamping (though delayed clamping for 30-60 seconds is now often preferred for neonatal benefit), and controlled cord traction with uterine countertraction, reduces postpartum hemorrhage risk compared to expectant management.

The fourth stage, sometimes called the immediate postpartum period, comprises the first 1-2 hours after placental delivery. During this time, the mother is monitored closely for hemorrhage, with regular assessment of vital signs, uterine fundus (should be firm and at or below the umbilicus), and vaginal bleeding.

<image>Panel A: Cervical dilation curve (Friedman pattern) plotting dilation against time with latent phase (slow, variable) and active phase (steeper, more predictable), comparing superimposed nulliparous and multiparous curves with duration ranges for each stage. Panel B: First stage showing progressive cervical dilation from 0 to 10 cm, and second stage showing maternal pushing efforts with fetal descent through the birth canal. Panel C: Third stage showing placental separation signs (gush of blood, cord lengthening, uterine firming) with active management components including uterotonic administration and delayed cord clamping technique. Panel D: Fourth stage monitoring elements including fundal massage technique, vital signs assessment every 15 minutes, and vaginal bleeding quantification during the first 1-2 hours postpartum.</image>

Section 3: Mechanisms of Labor - Cardinal Movements

The passage of the fetus through the birth canal requires a series of positional changes, classically described as the seven cardinal movements. These movements are continuous and overlapping rather than discrete steps, adapting the fetal diameters to the changing dimensions of the maternal pelvis.

Understanding fetal orientation requires precise terminology. Lie describes the relationship of the fetal spine to the maternal spine, either longitudinal (parallel, required for vaginal delivery) or transverse. Presentation refers to the fetal part entering the pelvic inlet first, most commonly cephalic (head) but alternatively breech (buttocks or feet) or shoulder. Position specifies the relationship of a designated point on the presenting part to the maternal pelvis, using a three-letter code: the first letter indicates left or right of maternal pelvis, the second indicates the presenting part landmark (occiput for cephalic, sacrum for breech), and the third indicates anterior, posterior, or transverse. Left occiput anterior (LOA) is the most common and favorable position.

Station measures the descent of the presenting part relative to the ischial spines, the narrowest pelvic diameter. Station 0 is at the level of the spines; negative stations (−1 to −3) indicate the presenting part is above the spines, while positive stations (+1 to +3) indicate descent below the spines. Engagement occurs when the widest diameter of the presenting part has passed through the pelvic inlet, generally corresponding to 0 station for cephalic presentations.

The cardinal movements proceed as follows. Engagement marks entry of the biparietal diameter into the pelvic inlet, typically in the transverse or oblique diameter. Descent continues throughout labor, driven by uterine contractions, maternal pushing, and gravity. Flexion brings the fetal chin to the chest, presenting the smallest cephalic diameter (suboccipitobregmatic, 9.5 cm) to the pelvis; this occurs passively as the head encounters pelvic resistance. Internal rotation turns the occiput from the transverse or oblique position to anterior (or less commonly, posterior), aligning the fetal head's anteroposterior diameter with the anteroposterior diameter of the pelvic outlet. Extension occurs as the occiput passes under the symphysis pubis and the head extends, with the forehead, face, and chin delivering over the perineum. External rotation (restitution) follows as the head rotates 45-90 degrees to realign with the shoulders, which have entered the pelvis in a transverse diameter and now rotate to anteroposterior for delivery. Expulsion completes the process as the anterior shoulder delivers under the symphysis, followed by the posterior shoulder and the body.

<image>Panel A: Engagement and descent showing biparietal diameter entering pelvic inlet in transverse position and progressing through the pelvis, with station measurements relative to ischial spines (-3 to +3) and fetal position nomenclature (LOA, ROA, OA, LOP, ROP). Panel B: Flexion with chin tucked to chest presenting the smallest suboccipitobregmatic diameter, followed by internal rotation turning the occiput from transverse to anterior alignment with the pelvic outlet. Panel C: Extension with occiput passing under the symphysis pubis and face delivering over the perineum, followed by external rotation/restitution with head realigning to shoulders. Panel D: Expulsion with anterior shoulder delivering under the symphysis and posterior shoulder following, with inset comparing cephalic diameters in flexed versus extended positions and view from below the pelvis showing occiput positions.</image>

Section 4: Fetal Heart Rate Monitoring

Intrapartum fetal heart rate (FHR) monitoring provides real-time assessment of fetal oxygenation status. Electronic fetal monitoring (EFM) has become nearly universal in developed countries, though intermittent auscultation remains appropriate for low-risk labors.

Baseline fetal heart rate is the average rate during a 10-minute segment, excluding accelerations, decelerations, and periods of marked variability. Normal baseline ranges from 110 to 160 beats per minute. Fetal tachycardia (>160 bpm) may reflect maternal fever, fetal infection, hypoxia, or medication effects. Fetal bradycardia (<110 bpm) may indicate cord compression, maternal hypotension, or fetal distress.

Baseline variability, defined as the fluctuations in FHR from beat to beat, represents the single most important indicator of fetal well-being. Moderate variability (6-25 bpm) indicates an intact fetal autonomic nervous system and adequate oxygenation. Minimal variability (≤5 bpm) may occur during fetal sleep (lasting 20-40 minutes), with certain medications (opioids, magnesium), or with fetal hypoxia/acidemia. Absent variability is concerning for significant fetal compromise. Marked variability (>25 bpm) is usually benign.

Accelerations, transient increases of at least 15 bpm lasting at least 15 seconds (or 10 bpm for 10 seconds in fetuses less than 32 weeks), are reassuring and indicate a reactive fetus. The presence of accelerations virtually excludes significant fetal acidemia.

Decelerations, transient decreases in FHR, are classified by their relationship to uterine contractions. Early decelerations mirror the contraction waveform, reaching nadir at the peak of the contraction; they result from fetal head compression causing vagal stimulation and are benign. Variable decelerations have abrupt onset and offset, variable timing relative to contractions, and variable shape; they result from umbilical cord compression and are common. Mild variables are generally well-tolerated, but severe, prolonged, or repetitive variables may indicate worsening fetal status. Late decelerations begin after the contraction peak and return to baseline after the contraction ends; they reflect uteroplacental insufficiency and, especially with absent variability, indicate fetal hypoxia.

The three-tier system categorizes FHR tracings for management. Category I (normal) includes baseline 110-160, moderate variability, no late or variable decelerations, with or without accelerations; routine care continues. Category II (indeterminate) encompasses tracings not meeting Category I or III criteria, requiring evaluation and continued surveillance. Category III (abnormal) includes absent variability with recurrent late or variable decelerations, bradycardia, or sinusoidal pattern; immediate evaluation and intervention are required, often including preparation for emergent delivery.

<image>Panel A: Baseline fetal heart rate assessment showing normal range 110-160 bpm on strip with variability categories illustrated (absent, minimal, moderate, marked) and amplitude measurements for each category. Panel B: Deceleration types with simultaneous contraction waveforms: early deceleration (mirrors contraction, nadir at peak, head compression), variable deceleration (abrupt onset/offset, variable timing and shape, cord compression), and late deceleration (onset after contraction peak, uteroplacental insufficiency). Panel C: Accelerations shown with reassuring significance (15 bpm for 15 seconds, or 10 bpm for 10 seconds before 32 weeks), virtually excluding significant fetal acidemia. Panel D: Three-tier category system with sample strip segments showing Category I (normal, routine care), Category II (indeterminate, evaluation needed), and Category III (abnormal, immediate intervention) with management approaches for each.</image>

Section 5: Intrauterine Resuscitation and Labor Induction

When Category II or III fetal heart rate patterns emerge, intrauterine resuscitation maneuvers aim to improve fetal oxygenation while determining the need for emergent delivery.

Position changes, particularly moving the mother to the left lateral position, relieve aortocaval compression by the gravid uterus, improving venous return and cardiac output and enhancing uteroplacental perfusion. If left lateral position is ineffective, right lateral or hands-and-knees positioning may help. Intravenous fluid bolus addresses potential hypovolemia and may improve uterine blood flow. Supplemental oxygen administration is commonly performed, though evidence for fetal benefit is limited. If oxytocin is infusing, it should be decreased or discontinued to reduce contraction frequency and intensity, allowing better interval oxygenation. Amnioinfusion, infusing saline into the amniotic cavity, is indicated for recurrent variable decelerations attributed to cord compression. Tocolysis with terbutaline or other agents may be used to stop contractions acutely in cases of uterine tachysystole (excessive contraction frequency) or to buy time before emergent cesarean.

Labor induction, the artificial initiation of labor before spontaneous onset, is performed when the benefits of delivery outweigh the risks of continuing pregnancy. Indications include maternal conditions (preeclampsia, diabetes, cardiac disease), fetal conditions (post-term pregnancy, intrauterine growth restriction, oligohydramnios), and obstetric conditions (premature rupture of membranes, chorioamnionitis). Elective induction at 39 weeks or later in low-risk nulliparous women with a favorable cervix has been shown to reduce cesarean delivery rates without increasing adverse outcomes (ARRIVE trial).

Contraindications to labor induction include placenta previa, vasa previa, umbilical cord prolapse, active genital herpes, prior classical cesarean or uterine rupture, and transverse fetal lie.

Cervical ripening prepares an unfavorable cervix (Bishop score <6) for induction. Pharmacologic methods include prostaglandins: misoprostol (PGE1 analog) given vaginally or orally, and dinoprostone (PGE2) as vaginal insert or gel. Mechanical methods include Foley catheter balloon placed through the cervix into the lower uterine segment, which provides cervical dilation through mechanical pressure. Membrane stripping, performed during cervical examination by separating the membranes from the lower uterine segment, releases local prostaglandins and may hasten spontaneous labor onset.

Oxytocin is administered intravenously to induce or augment labor once the cervix is favorable. Dosing begins low and is titrated upward at defined intervals to achieve adequate contractions (typically 3 in 10 minutes) without tachysystole.

<image>Panel A: Intrauterine resuscitation flowchart beginning with abnormal FHR tracing, showing position change (left lateral decubitus with aortocaval relief), IV fluid bolus, oxygen supplementation, and oxytocin discontinuation. Panel B: Advanced resuscitation interventions including amnioinfusion (saline infusing into amniotic cavity via intrauterine catheter for recurrent variable decelerations) and terbutaline injection for acute tocolysis, with reassessment and decision point for delivery. Panel C: Labor induction indications (maternal: preeclampsia, diabetes; fetal: postterm, IUGR, oligohydramnios; obstetric: PROM, chorioamnionitis) with Bishop score assessment leading to favorable (proceed to oxytocin) or unfavorable (cervical ripening needed). Panel D: Cervical ripening methods including misoprostol tablet, dinoprostone insert, and Foley balloon placement with cross-sectional diagram, followed by oxytocin infusion protocol with titration schedule.</image>

Section 6: Cesarean Delivery

Cesarean delivery, the surgical birth of a fetus through incisions in the abdominal wall and uterus, is the most common major surgery performed in the United States, with rates exceeding 30% of all deliveries.

Indications for cesarean delivery are broadly categorized. Labor abnormalities include arrest of dilation (no cervical change for 4 or more hours with adequate contractions and ruptured membranes) and arrest of descent (no progress for 1-2 hours of pushing in the second stage). Fetal indications include non-reassuring fetal heart rate tracing not responsive to resuscitation, malpresentation (breech, transverse lie), and macrosomia in the setting of diabetes. Placental indications include placenta previa and placenta accreta spectrum. Maternal indications include prior classical cesarean incision, certain cardiac conditions, and active herpes outbreak. Other indications include umbilical cord prolapse, failed operative vaginal delivery, and mechanical obstruction (large fibroids, pelvic mass).

The uterine incision type has significant implications for future pregnancies. The low transverse incision, made horizontally in the lower uterine segment, is used in the vast majority of cesareans. This incision is in the thinnest, least contractile portion of the uterus and carries the lowest risk of rupture in subsequent pregnancies (0.5-1%), making trial of labor after cesarean (TOLAC) a consideration. The classical (vertical) incision extends into the thick, contractile upper uterine segment and carries a 4-9% rupture risk in subsequent labor, making repeat cesarean mandatory. Low vertical incisions are less common and may or may not preclude subsequent labor depending on extension into the upper segment.

Trial of labor after cesarean (TOLAC) is an option for many women with prior low transverse cesarean. Candidates include those with one or two prior low transverse cesareans, no history of uterine rupture, and no contraindications to vaginal delivery. Success rates (vaginal birth after cesarean, VBAC) range from 60-80% depending on multiple factors, with prior vaginal delivery being the strongest predictor of success. Uterine rupture, occurring in approximately 0.5-1% of TOLAC attempts, is the major concern, presenting with fetal heart rate abnormalities (most common sign), loss of station, abdominal pain, and vaginal bleeding.

Risks of cesarean delivery include hemorrhage, infection (endometritis, wound infection), thromboembolic disease, and surgical injury to bladder, bowel, or ureters. Long-term risks include increased abnormal placentation (accreta spectrum) and adhesive disease in subsequent pregnancies.

<image>Panel A: Cesarean indications organized by category including labor abnormalities (arrest of dilation and descent definitions), fetal indications (non-reassuring FHR, malpresentation), and placental indications (previa, accreta spectrum). Panel B: Uterine incision types showing low transverse (most common, horizontal in lower segment, 0.5-1% rupture risk) versus classical (vertical into upper segment, 4-9% rupture risk) with surgical view of cesarean procedure layers. Panel C: TOLAC candidate criteria checklist, success rate factors (60-80% VBAC rate, prior vaginal delivery most predictive), and uterine rupture signs (FHR abnormalities, loss of station, pain, bleeding). Panel D: Decision pathway for mode of delivery in women with prior cesarean, showing contraindications to TOLAC and mandatory repeat cesarean for classical incision history.</image>

Section 7: Operative Vaginal Delivery

Operative vaginal delivery, using forceps or vacuum to assist the final expulsion of the fetus, remains an important skill for managing prolonged second stage or compromised fetuses when vaginal delivery is imminent.

Forceps, metal instruments with two articulating blades, are applied to the fetal head and used to provide traction and, in some cases, rotation. Various forceps types exist, with Simpson forceps commonly used for molded heads and Tucker-McLane for unmolded heads. Vacuum devices apply suction to the fetal scalp via a cup (rigid or soft), allowing traction along the pelvic curve.

Strict prerequisites must be met before operative delivery. The cervix must be completely dilated and membranes ruptured. The fetal head must be engaged (station +2 or lower preferred). Fetal position must be known with certainty. The maternal pelvis must be adequate. Adequate anesthesia must be present. Informed consent must be obtained. The operator must be willing and able to perform cesarean delivery if the operative attempt fails.

Indications for operative vaginal delivery include prolonged second stage (duration exceeding expected norms), maternal exhaustion or medical conditions limiting pushing (such as cardiac disease), and non-reassuring fetal heart rate tracing when vaginal delivery is imminent.

Classification by station at application defines outlet (scalp visible without separating labia, head on perineum), low (station +2 or greater), and mid-pelvic (station 0 to +2) deliveries. Outlet and low deliveries are most common; mid-pelvic and rotational deliveries carry higher complication rates and require considerable expertise.

Complications differ between instruments. Forceps-associated complications include maternal lacerations (third and fourth degree tears more common), neonatal facial nerve palsy (usually transient), and rarely skull fractures. Vacuum-associated complications include scalp lacerations, cephalohematoma (subperiosteal bleeding, common but benign), and subgaleal hemorrhage (bleeding beneath the scalp aponeurosis into the potential space overlying the skull, a rare but potentially life-threatening complication due to massive blood loss).

<image>Panel A: Operative instruments showing forceps (Simpson and Tucker-McLane types with blade anatomy labeled) and vacuum devices (rigid cup versus soft cup designs), with prerequisites checklist for operative vaginal delivery. Panel B: Application technique showing forceps blades positioned on fetal head with correct orientation landmarks, and vacuum cup placed on the flexion point with traction direction indicated. Panel C: Station classification diagram showing outlet, low, and mid-pelvic levels relative to ischial spines with corresponding risk levels for each classification. Panel D: Complications including maternal laceration degrees, forceps-associated facial nerve palsy (facial diagram with affected areas), and vacuum-associated scalp findings with cross-sections differentiating cephalohematoma (subperiosteal, contained) from subgaleal hemorrhage (beneath aponeurosis, spreads diffusely).</image>

Section 8: Labor Complications - Dystocia and Shoulder Dystocia

Labor dystocia, abnormally slow or arrested labor progress, is the most common indication for primary cesarean delivery. Understanding the causes and management is essential for safe obstetric practice.

The "three Ps" framework categorizes dystocia causes. Power refers to uterine contractile forces, which may be inadequate in strength, frequency, or coordination. Assessment includes monitoring contraction pattern (ideally 3 in 10 minutes) and, when needed, direct measurement of intrauterine pressure via internal tocodynamometry. Augmentation with oxytocin addresses inadequate power. Passenger factors include fetal size (macrosomia), presentation (malpresentation), and position (occiput posterior positions often result in slower labor). Passage refers to the bony pelvis and soft tissues; while true cephalopelvic disproportion is rare, it can prevent vaginal delivery.

Arrest disorders are defined precisely. Arrest of active phase labor requires no cervical change for at least 4 hours with adequate contractions (and ruptured membranes) or 6 hours with inadequate contractions despite augmentation. Arrest of descent in the second stage requires no progress for at least 1 hour of pushing in multiparous women or 2 hours in nulliparous women (or longer with epidural).

Shoulder dystocia, impaction of the anterior fetal shoulder behind the maternal pubic symphysis after delivery of the head, is an obstetric emergency occurring in 0.5-1% of vaginal deliveries. Risk factors include fetal macrosomia (particularly >4000-4500 g), maternal diabetes, maternal obesity, prolonged second stage, and prior shoulder dystocia, though many cases occur without identifiable risk factors.

The turtle sign, retraction of the delivered fetal head against the perineum between contractions, heralds shoulder dystocia. Management requires rapid, systematic maneuvers. The McRoberts maneuver, hyperflexion of the maternal thighs against the abdomen, straightens the sacrum and rotates the symphysis cephalad, increasing the anteroposterior diameter of the pelvic outlet; this is the first maneuver performed. Suprapubic pressure, applied by an assistant behind the anterior fetal shoulder, pushes the shoulder anteriorly toward the fetal chest, reducing the bisacromial diameter; this is performed simultaneously with McRoberts. If these fail, rotational maneuvers follow: the Woods corkscrew rotates the posterior shoulder anteriorly, and the Rubin maneuver adducts the fetal shoulders by pushing the accessible shoulder toward the fetal chest. Delivery of the posterior arm, sweeping the fetal arm across the chest and delivering it, reduces the presenting shoulder diameter. The Gaskin maneuver (all-fours position) uses gravity and position change.

Complications of shoulder dystocia include brachial plexus injury (Erb's palsy affecting C5-C6 with waiter's tip posture; Klumpke's palsy affecting C8-T1), clavicle or humerus fracture, and hypoxic injury if prolonged. Most brachial plexus injuries resolve within the first year.

<image>Panel A: The three Ps of dystocia showing power (contraction frequency/strength with tocodynamometer tracing), passenger (fetal size estimation and position variants), and passage (pelvic shapes), with arrest of dilation and descent definitions and criteria. Panel B: Shoulder dystocia recognition with turtle sign illustration, and initial maneuvers including McRoberts position (maternal thigh hyperflexion with pelvic angle change) and simultaneous suprapubic pressure (direction of push on anterior shoulder). Panel C: Advanced maneuvers including Woods corkscrew (rotation of posterior shoulder anteriorly), Rubin maneuver (shoulder adduction), delivery of posterior arm (sweeping motion across chest), and Gaskin all-fours position using gravity and position change. Panel D: Complications showing brachial plexus injury anatomy with Erb's palsy (C5-C6, waiter's tip posture) and Klumpke's palsy (C8-T1), plus clavicle/humerus fracture and hypoxic injury risk with prolonged dystocia.</image>

Section 9: Cord Prolapse, Uterine Rupture, and Anesthesia

Umbilical cord prolapse, descent of the umbilical cord ahead of the presenting fetal part, threatens immediate fetal life through cord compression and vasospasm. The overt form occurs when the cord protrudes through the cervix into the vagina, while occult prolapse involves the cord alongside the presenting part. Risk factors include ruptured membranes with an unengaged presenting part, malpresentation, polyhydramnios, and multiparity.

Management of cord prolapse requires immediate action. The examiner's hand should elevate the presenting part off the cord, maintained continuously until delivery. The patient is placed in knee-chest or steep Trendelenburg position to reduce pressure on the cord. The bladder may be filled with saline to elevate the presenting part. Tocolysis may reduce cord compression. Emergency cesarean delivery is performed unless vaginal delivery is truly imminent (complete dilation, engaged vertex).

Uterine rupture, disruption of the uterine wall during labor, is a catastrophic complication. The risk is highest in women with prior uterine surgery, particularly classical cesarean incision, but can occur in unscarred uteri. Signs include sudden severe abdominal pain (often between contractions), fetal heart rate abnormalities (most common and often earliest sign, particularly prolonged bradycardia), loss of station (fetal parts may be palpable through the abdomen), vaginal bleeding, and cessation of contractions. Management requires emergency laparotomy with delivery, followed by repair or hysterectomy depending on the extent of rupture and patient stability.

Labor analgesia ranges from non-pharmacologic methods (support, positioning, hydrotherapy, breathing techniques) to systemic opioids (fentanyl, morphine) to regional anesthesia. Epidural analgesia, the most effective method, involves placement of a catheter in the epidural space at L3-L4 or L4-L5, allowing continuous or patient-controlled administration of local anesthetic (bupivacaine, ropivacaine) and opioid (fentanyl). Combined spinal-epidural provides rapid onset through spinal injection with subsequent epidural availability.

Epidural complications include hypotension (most common, managed with fluids and vasopressors), inadequate or patchy block, post-dural puncture headache (if dura is inadvertently punctured), and rarely high block, epidural hematoma, or abscess. Motor block may impair pushing, potentially prolonging the second stage. Epidural analgesia does not significantly increase cesarean delivery rates but may modestly prolong the first and second stages of labor.

<image>Panel A: Cord prolapse showing cross-sectional diagram of prolapsed cord compressed between fetal head and cervix, with management steps including hand elevating presenting part, knee-chest position, and bladder filling with catheter leading to emergency cesarean. Panel B: Uterine rupture showing uterus with rupture site and fetal parts extruding, warning signs (FHR abnormalities, pain, loss of station, bleeding), and surgical decision point between rupture repair and hysterectomy. Panel C: Epidural analgesia showing lumbar spine cross-section with catheter placement in epidural space at L3-L4 or L4-L5, dermatome coverage map, and combined spinal-epidural technique with both needles. Panel D: Regional anesthesia complications including hypotension (most common, managed with fluids and vasopressors), post-dural puncture headache (with blood patch treatment), and effects on labor progress.</image>

Section 10: Third Stage, Fourth Stage, and Immediate Newborn Care

The third stage of labor, from infant delivery to placental expulsion, normally lasts less than 30 minutes. Active management, now standard practice, significantly reduces postpartum hemorrhage risk. Uterotonic administration (typically oxytocin 10 units IV or IM) is given after delivery of the anterior shoulder or immediately after infant delivery. Delayed cord clamping (30-60 seconds) allows transfusion of placental blood to the neonate, improving iron stores and hemoglobin levels, particularly beneficial for preterm infants. Controlled cord traction, with counter-pressure on the uterus to prevent inversion, facilitates placental delivery.

Perineal trauma is common during vaginal delivery and is classified by depth. First-degree lacerations involve only the vaginal mucosa or perineal skin. Second-degree lacerations extend into the perineal body musculature but spare the anal sphincter. Third-degree lacerations involve the anal sphincter complex (partial or complete). Fourth-degree lacerations extend through the sphincter into the rectal mucosa. Third and fourth-degree lacerations are associated with operative vaginal delivery, midline episiotomy (more so than mediolateral), and macrosomia.

Episiotomy, surgical incision of the perineum, is no longer performed routinely. When indicated (impending severe laceration, need for rapid delivery), mediolateral incision carries lower risk of sphincter extension than midline, though healing is more painful. Selective use has reduced overall episiotomy rates dramatically.

The fourth stage encompasses the first 1-2 hours postpartum, the highest-risk period for postpartum hemorrhage. Monitoring includes vital signs every 15 minutes initially, fundal assessment (should be firm and at or below the umbilicus; a soft, "boggy" fundus suggests atony), and quantification of vaginal bleeding.

Immediate newborn care begins with assessment of the need for resuscitation. Most term newborns require only warmth (drying, skin-to-skin contact), clearing the airway as needed, and stimulation. The Apgar score, assessed at 1 and 5 minutes, evaluates appearance (color), pulse (heart rate), grimace (reflex irritability), activity (muscle tone), and respiration; each component receives 0-2 points. While useful for communication, the Apgar score should not delay resuscitation. Prophylactic measures include erythromycin ophthalmic ointment to prevent gonococcal ophthalmia neonatorum and intramuscular vitamin K to prevent vitamin K deficiency bleeding.

<image>Panel A: Active management of third stage showing oxytocin administration timing, delayed cord clamping (30-60 seconds) with blood transfusion to neonate, and controlled cord traction with counter-pressure technique to prevent uterine inversion. Panel B: Laceration classification in cross-sectional diagrams from first degree (mucosa/skin only) through fourth degree (into rectal mucosa), with episiotomy types compared (midline versus mediolateral and extension risks). Panel C: Fourth stage monitoring showing vital signs frequency (every 15 minutes), fundal assessment technique comparing firm versus boggy fundus, and vaginal bleeding quantification during the first 1-2 hours. Panel D: Immediate newborn care including Apgar scoring chart with five components (appearance, pulse, grimace, activity, respiration), erythromycin eye prophylaxis, vitamin K injection, and skin-to-skin contact emphasis.</image>

Summary

Labor initiation involves complex hormonal changes: functional progesterone withdrawal, increasing estrogen-to-progesterone ratio, prostaglandin production, and oxytocin release. The Bishop score predicts inducibility based on cervical dilation, effacement, station, consistency, and position.

Labor progresses through four stages: first stage (latent 0-6 cm and active 6-10 cm phases), second stage (complete dilation to delivery), third stage (placental delivery), and fourth stage (immediate postpartum monitoring).

The cardinal movements—engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion—describe fetal passage through the birth canal.

Fetal heart rate monitoring assesses baseline (110-160 bpm normal), variability (moderate is reassuring), accelerations (reassuring), and decelerations (early = head compression, variable = cord compression, late = uteroplacental insufficiency). The three-tier category system guides management.

Labor induction indications include maternal, fetal, and obstetric conditions. Cervical ripening (prostaglandins, Foley balloon) precedes oxytocin when the cervix is unfavorable.

Cesarean delivery is indicated for arrest disorders, non-reassuring fetal status, malpresentation, and placental abnormalities. Low transverse uterine incision allows consideration of TOLAC in future pregnancies.

Shoulder dystocia requires rapid, sequential maneuvers: McRoberts positioning, suprapubic pressure, rotational maneuvers, and posterior arm delivery.

Key Terms

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