22.2 Labor & Parturition: Signs of Labor, Pelvis and Passenger, Stages and Cardinal Movements, Partograph, Fetal Monitoring, Dystocia, Shoulder Dystocia, Operative Delivery, Preterm Labor, PROM and Adolescent Pregnancy

Why this area matters

TOS area A asks you to:

• recognize the burden and risk factors of abnormal labor;
• differentiate labor, preterm labor and preterm premature rupture of membranes;
• apply the partogram and interpret intrapartum fetal monitoring;
• identify complications such as dysfunctional labor;
• plan interventions that improve maternal and perinatal outcomes.

Obstructed and prolonged labor remains an important cause of maternal death and of fistula, uterine rupture and birth asphyxia where women deliver far from emergency obstetric care. The DOH requires facility-based delivery with skilled birth attendants for this reason. Adolescent pregnancy is a national priority (Executive Order 141, 2021).

Signs of labor and essential intrapartum care

• True labor:
  • regular contractions that increase in frequency, duration and intensity;
  • pain from the back to the front;
  • progressive effacement and dilation of the cervix;
  • often a "bloody show" (blood-stained mucus plug).
• False labor (Braxton Hicks): irregular contractions with no cervical change that ease with rest or hydration.
• DOH Administrative Order 2019-0034 on essential intrapartum care:
  • admit healthy women in labor at the active phase: 4 cm with 3 to 4 contractions in 10 minutes;
  • provide respectful maternity care;
  • allow a companion of choice, oral fluids and food, and freedom of movement and upright birth positions;
  • avoid routine interventions such as enemas, shaving, routine amniotomy, routine episiotomy and fundal pressure;
  • do not accelerate labor in healthy women without an indication.

The passage and the passenger

• Pelvic types:
  • the gynecoid pelvis, round, is the most favorable;
  • the android pelvis, heart-shaped, favors deep transverse arrest and occiput posterior positions;
  • the anthropoid pelvis is oval anteroposteriorly;
  • the platypelloid pelvis is flat.
• Pelvic inlet:
  • the obstetric conjugate is the shortest anteroposterior diameter of the inlet, normally 10 cm or more;
  • it is estimated as the diagonal conjugate (normally 11.5 cm or more) minus 1.5 to 2 cm.
• Midpelvis: the interspinous diameter, about 10 cm, is the smallest diameter of the pelvis.
• Station is measured in centimeters above or below the ischial spines (0 = engaged).
• The fetal head:
  • the suboccipitobregmatic diameter (9.5 cm) presents in a well-flexed vertex;
  • the occipitofrontal diameter (11.5 cm) presents in a deflexed head;
  • the occipitomental diameter (13.5 cm) presents in a brow presentation, which cannot deliver vaginally at term.

Labor Mechanics, Stages & Cardinal Movements

Labor is defined as regular, painful uterine contractions resulting in progressive cervical effacement and dilation.

The Three Stages of Labor

1. First Stage (Cervical Stage): Begins with the onset of regular uterine contractions and ends with complete cervical dilation (10 cm).
   • Latent Phase: Characterized by gradual cervical softening and effacement with slow dilation up to 4-6 cm.
   • Active Phase: Begins at 5 to 6 cm dilation, characterized by rapid cervical dilation. Friedman's classic minimum rates were 1.2 cm/hr in nulliparas and 1.5 cm/hr in multiparas, and the WHO partograph alert line assumes 1 cm/hr. Newer data show that many normal labors progress more slowly before 6 cm, so arrest is not diagnosed early in the active phase.
2. Second Stage (Fetal Expulsion Stage): Begins with complete cervical dilation (10 cm) and ends with the delivery of the neonate. The classic definition of a prolonged second stage is more than 2 hours in nulliparas and 1 hour in multiparas (one more hour with epidural analgesia). Current ACOG guidance allows at least 3 hours of pushing in nulliparas and 2 hours in multiparas before diagnosing arrest, if mother and fetus are well.
3. Third Stage (Placental Stage): Begins immediately following neonatal delivery and ends with the complete expulsion of the placenta and fetal membranes. Normal duration is $<30$ minutes.

The Cardinal Movements of Labor

For a fetus presenting in the cephalic vertex position, negotiating the curved maternal pelvis (curve of Carus) requires seven sequential biomechanical movements:

1. Engagement: The biparietal diameter (the greatest transverse diameter of the fetal head, measuring 9.5 cm) passes through the maternal pelvic inlet. Clinically, the lowest bony point of the occiput reaches station 0 (level of maternal ischial spines).
2. Descent: Downward movement of the presenting part through the birth canal, occurring progressively throughout labor.
3. Flexion: As the descending head meets resistance from the cervix, pelvic sidewalls, and muscular pelvic floor, the chin is pressed firmly against the fetal chest. This substitutes the smaller suboccipitobregmatic diameter (9.5 cm) for the larger occipitofrontal diameter (11.5 cm).
4. Internal Rotation: The fetal occiput rotates anteriorly from an occiput transverse (OT) or oblique position toward the pubic symphysis (occiput anterior / OA) to align with the widest diameter of the pelvic outlet.
5. Extension: As the sharply flexed head crowns and reaches the vulva, the suboccipital region pivots beneath the inferior margin of the pubic symphysis. Upward extension delivers the occiput, bregma, forehead, nose, mouth, and chin over the perineum.
6. External Rotation (Restitution): Following delivery, the head spontaneously rotates 45 to 90 degrees back to align with the fetal spine and shoulders (transverse to the maternal pelvis).
7. Expulsion: The anterior shoulder delivers beneath the pubic symphysis, followed by the posterior shoulder sweeping over the perineum, and the remainder of the fetal trunk is rapidly expelled.

The partograph and labor abnormalities

• The WHO partograph plots, against time:
  • cervical dilation and descent;
  • contractions;
  • fetal heart rate and amniotic fluid;
  • maternal vital signs, drugs and urine.
• Alert and action lines: the alert line assumes 1 cm per hour in the active phase. Crossing it prompts closer assessment or referral. The action line, 4 hours to its right, prompts intervention.
• Causes of abnormal labor: dystocia comes from the powers (hypotonic contractions, the most correctable cause), the passenger (macrosomia, malposition such as persistent occiput posterior, malpresentation, anomalies) or the passage (contracted pelvis, soft-tissue obstruction).
• Arrest of the active phase: at 6 cm or more with ruptured membranes, no cervical change for 4 hours or more despite adequate contractions, or 6 hours or more with inadequate contractions despite oxytocin. It is an indication for cesarean delivery.
• Management: amniotomy and oxytocin augmentation correct hypotonic labor. Cephalopelvic disproportion and obstructed labor need cesarean delivery. Signs of obstruction: a Bandl retraction ring, a distended lower segment, caput and molding with no descent, and maternal exhaustion. These warn of impending uterine rupture.

Electronic Fetal Heart Rate Monitoring

Cardiotocography assesses fetal oxygenation and acid-base balance by correlating Fetal Heart Rate (FHR) with uterine contractions.

• Baseline FHR: Normal is 110 to 160 bpm. Bradycardia is $<110\text{ bpm}$; tachycardia is $>160\text{ bpm}$.
• Baseline Variability: Fluctuations in baseline FHR irregular in amplitude and frequency. Absent (undetectable), minimal ($<5\text{ bpm}$), moderate (6 to 25 bpm, normal/reassuring), marked ($>25\text{ bpm}$).
• Deceleration Patterns:
  • Early Decelerations: Symmetric, gradual decrease and return of FHR mirroring the uterine contraction (nadir of deceleration aligns with the peak of the contraction). Cause: Fetal head compression triggering a benign vagal reflex. Normal, benign, requires no intervention.
  • Variable Decelerations: Abrupt decrease in FHR ($<30\text{ seconds}$ from onset to nadir), lasting $\ge 15\text{ seconds}$ and $<2\text{ minutes}$, with a drop of $\ge 15\text{ bpm}$. Vary in timing, depth, and duration relative to contractions. Cause: Umbilical cord compression. Corrective measures include maternal repositioning and amnioinfusion.
  • Late Decelerations: Gradual decrease in FHR beginning after the contraction starts, with the nadir occurring after the contraction peak, recovering after the contraction ends. Cause: Uteroplacental insufficiency causing fetal hypoxia. Requires immediate intrauterine resuscitation (oxygen, IV fluid bolus, maternal lateral repositioning, stopping oxytocin).

The Three-Tier NICHD Fetal Heart Rate Interpretation System

• Category I (Normal / Reassuring): Baseline 110-160 bpm, moderate variability, absence of late or variable decelerations; early decelerations may be present or absent. Highly predictive of normal umbilical cord arterial pH.
• Category II (Indeterminate): FHR patterns not classified as Category I or III (e.g., minimal variability, absent accelerations after fetal stimulation, tachycardia, recurrent variable decelerations with moderate variability). Requires continuous evaluation and corrective measures.
• Category III (Abnormal): Absent baseline variability accompanied by recurrent late decelerations, recurrent variable decelerations, or bradycardia; OR a sinusoidal pattern (smooth, undulating sine-wave-like pattern associated with severe fetal anemia or fetomaternal hemorrhage). Predicts abnormal fetal acidemia and mandates emergent delivery.

In low-resource settings, intermittent auscultation every 15 to 30 minutes in the first stage and every 5 minutes in the second stage is acceptable for low-risk labor.

Dystocia and Shoulder Dystocia

Dystocia represents abnormal labor progression or mechanical arrest resulting from abnormalities in the "3 Ps": Powers (inadequate uterine contractility), Passenger (fetal macrosomia, malpresentation, malposition), or Passage (contracted maternal bony pelvis or soft tissue obstruction).

Shoulder Dystocia Emergency Management

Shoulder dystocia occurs when the anterior fetal shoulder becomes impacted behind the maternal pubic symphysis following delivery of the fetal head.

• Diagnosis: Delivery of the head is accompanied by the "turtle sign" (the fetal head retracts tightly against the maternal perineum). Time is critical: the cord is compressed and the fetus cannot breathe, so the risk of hypoxic injury rises as the head-to-body delivery interval lengthens.
• THE CARDINAL ERROR: DO NOT APPLY FUNDAL PRESSURE. Fundal pressure further impacts the anterior shoulder behind the pubic bone, increases the risk of severe brachial plexus avulsion (Erb-Duchenne palsy, C5-C6), and causes uterine rupture.
• The HELPERR Clinical Maneuver Protocol:
  1. H - Call for Help: Alert obstetrics, anesthesia, nursing, and neonatal resuscitation teams.
  2. E - Evaluate for Episiotomy: Episiotomy does not relieve the bony obstruction but provides room for internal manual manipulations.
  3. L - Legs (McRoberts Maneuver): Hyperflex and abduct the maternal hips firmly against the maternal abdomen. This flattens the sacral promontory and cephalad-rotates the pubic symphysis, successfully resolving over 40% of shoulder dystocias.
  4. P - Suprapubic Pressure (Rubin I): An assistant applies firm downward and lateral pressure with the heel of the hand just above the pubic symphysis to push the anterior shoulder into an oblique pelvic diameter. (Never fundal pressure!).
  5. E - Enter (Internal Rotational Maneuvers):
     • Rubin II Maneuver: Two fingers insert into the vagina behind the anterior shoulder, applying pressure toward the fetal chest to adduct the shoulder.
     • Woods Screw Maneuver: Two fingers place against the anterior surface of the posterior shoulder, rotating the posterior shoulder 180 degrees in a corkscrew fashion.
  6. R - Remove the Posterior Arm: The operator inserts a hand along the posterior hollow of the sacrum, grasps the fetal wrist or hand, sweeps the arm across the fetal chest, and delivers the posterior arm over the perineum, reducing the bisacromial diameter by 2 to 3 cm.
  7. R - Roll the Patient (Gaskin Maneuver): Place the mother in the "all-fours" position on hands and knees.
  8. Last-resort Maneuvers: Intentional clavicular fracture, Zavanelli maneuver (cephalic replacement: flexing the head back into the vagina followed by emergency STAT Cesarean delivery), or symphysiotomy.

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Operative Obstetrics & Trial of Labor After Cesarean (TOLAC)

Operative Vaginal Delivery (Vacuum Extractor and Forceps)

Indicated for prolonged second stage of labor, maternal exhaustion, or non-reassuring fetal status during the second stage.

• Mandatory Prerequisites: Completely dilated cervix (10 cm), ruptured membranes, engaged head (station 0 or lower; most procedures are low or outlet deliveries at station +2 or lower), exact determination of fetal position, empty maternal bladder, adequate maternal analgesia, and willingness to abandon the procedure if traction fails.
• Complications: Vacuum extraction carries higher risks of neonatal cephalohematoma, subgaleal hematoma (bleeding beneath the epicranial aponeurosis that can hold the entire neonatal blood volume), and retinal hemorrhages. Forceps carry higher risks of maternal 3rd- and 4th-degree perineal lacerations and neonatal facial nerve (CN VII) palsy.

Cesarean Delivery and TOLAC Guidelines

• Absolute Indications for Cesarean: Complete placenta previa, vasa previa, active primary genital herpes lesions, transverse fetal lie, pelvic structural obstruction, and prior classical uterine incision.
• TOLAC Candidates: Women with one prior low transverse cesarean incision, clinically adequate pelvis, and immediate access to a facility equipped for emergency laparotomy.
• Contraindications to TOLAC:
  • Prior classical (vertical) incision (uterine rupture risk is 4% to 9%, compared to 0.5% to 0.9% for a low transverse incision).
  • Prior T-shaped or J-shaped incision, or prior extensive transmural myomectomy entering the endometrial cavity.
  • Prior uterine rupture.
  • Prostaglandins (Misoprostol, Dinoprostone) are STRICTLY CONTRAINDICATED for cervical ripening or labor induction in TOLAC patients due to a dramatic increase in uterine rupture risk.

Preterm labor

• Definition: regular contractions with cervical change between 20 and 36 6/7 weeks.
• Risk factors:
  • previous preterm birth (the strongest);
  • short cervix on ultrasound (25 mm or less);
  • multiple gestation;
  • infection (bacteriuria, bacterial vaginosis, chorioamnionitis);
  • bleeding;
  • adolescent or advanced maternal age;
  • smoking and poor nutrition.
• Management at 24 to 34 weeks:
  • antenatal corticosteroids: betamethasone 12 mg IM, 2 doses 24 hours apart, or dexamethasone 6 mg IM every 12 hours for 4 doses;
  • tocolysis for up to 48 hours to allow the steroids to act: nifedipine, or indomethacin before 32 weeks (it can close the ductus arteriosus and cause oligohydramnios);
  • magnesium sulfate for fetal neuroprotection before 32 weeks, which reduces cerebral palsy;
  • GBS prophylaxis if GBS status is unknown or positive.
• Prevention: vaginal progesterone for a short cervix, cervical cerclage for selected women with a previous preterm birth or cervical insufficiency, and treatment of bacteriuria.

Premature rupture of membranes

• Definitions: PROM is rupture before the onset of labor. Preterm PROM (PPROM) is rupture before 37 weeks.
• Diagnosis: sterile speculum examination shows fluid pooling in the posterior fornix, alkaline pH on nitrazine paper (pH 7.0 to 7.5) and ferning on a dried slide. Ultrasound may show oligohydramnios. Avoid digital examination in PPROM because it increases infection and shortens latency.
• Term PROM: induce labor with oxytocin rather than wait, which lowers infection rates. Give GBS prophylaxis if indicated.
• PPROM before 34 weeks without infection or fetal compromise:
  • expectant management;
  • latency antibiotics (IV ampicillin and erythromycin, then oral amoxicillin and erythromycin, for 7 days);
  • corticosteroids;
  • magnesium sulfate before 32 weeks;
  • delivery at 34 weeks or earlier if complications develop.
• Chorioamnionitis (maternal fever with fetal tachycardia, uterine tenderness or purulent fluid) requires broad-spectrum antibiotics and delivery.

Adolescent pregnancy

Pregnant adolescents, especially those under 16, have higher risks of:

• anemia;
• preeclampsia;
• preterm birth and low birth weight;
• cephalopelvic disproportion and obstructed labor;
• STIs, depression, interrupted schooling and repeat pregnancy.

Care includes early registration, nutrition support, screening for sexual abuse (under RA 11648, sexual intercourse with a child under 16 is statutory rape, apart from a narrow close-in-age exception), confidential counseling and postpartum contraception. Under Executive Order 141 (2021), preventing adolescent pregnancy is a whole-of-government national priority.