Normal labor and delivery

Last updated: October 13, 2022

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Childbirth begins with the onset of labor, which consists of contractions that lead to progressive cervical dilation and effacement, eventually resulting in the birth of the infant and expulsion of the placenta. The process of normal childbirth depends on a high degree of anatomical and physiological compatibility between the mother and child. The birth canal is the passage consisting of the mother's bony pelvis and soft tissues through which a fetus passes during vaginal delivery. Fetal orientation during childbirth is described in terms of lie, presenting part, position, attitude of the presenting part, and station. The clinical status of the mother and fetus should be consistently monitored during labor and delivery. While vaginal delivery is typically preferred, cesarean delivery may be indicated under certain circumstances. Complications of normal vaginal delivery include perineal lacerations, hemorrhage, nerve injuries, and coccydynia.

See “Abnormal labor and delivery” for intrapartum complications and their management.

Fetal lie

  • Definition: relation of the fetal long axis to the long axis of the maternal uterus
  • Types
    • Longitudinal lie: fetus is in the same axis (most common)
    • Transverse lie: fetus is at a 90° angle
    • Oblique lie: fetus is at a 45° angle

Fetal presentation

  • Definition: part of the fetus that overlies the maternal pelvic inlet
  • Types
    • Cephalic presentation: head (most common)
    • Breech presentation: buttocks or feet
      • Frank breech: flexed hips and extended knees (buttocks presenting)
      • Complete breech: thighs and legs flexed (cannonball position)
      • Single Footling breech: hip of one leg is flexed and the knee of the other is extended (one foot presenting)
      • Double Footling breech: both thighs and legs are extended (feet presenting)
    • Compound presentation: ≥ 1 anatomical presenting part (e.g., cephalic or breech presentation with presentation of an extremity)
    • Shoulder presentation: shoulder presentations combined with a transverse or oblique lie

Fetal position

  • Definition: relationship and orientation (i.e., fetal occiput pointing towards maternal left or right) of the presenting fetal part to the maternal pelvis
  • Types
    • Occiput anterior position: Fetal occiput points towards maternal symphysis pubis; fetus faces downwards.
      • Left occiput anterior (LOA): Fetal back faces the maternal left, anterior fontanelle faces the maternal right, sagittal suture lies in the right oblique diameter; (most common position).
      • Right occiput anterior (ROA): Fetal back faces the maternal right, anterior fontanelle faces the maternal left, sagittal suture lies in the left oblique diameter.
    • Occiput posterior position: Fetal occiput points towards the maternal sacral promontory with face to pubis symphysis; the fetus faces upward
    • Sacrum in breech presentation
    • Mentum (chin) in extended cephalic (face) presentation

Fetal attitude [1]

  • Definition: degree of extension/flexion of the fetal head during cephalic presentation
  • Types
    • Vertex presentation (maximally flexed); most common attitude
    • Brow presentation (partially extended)
    • Face presentation (maximally extended)
    • Forehead presentation (partially flexed; military attitude): Spontaneous vaginal delivery is possible .

Station (Obstetrics) [2]

  • Definition: measurement (in cm) of the presenting part above and below the maternal ischial spine
    Station Description
    0 the presenting part is at the level of the ischial spines
    -1, -2, -3 1, 2, and 3 cm above the level of the ischial spines, respectively
    +1, +2, +3 1, 2, and 3 cm below the level of the ischial spines, respectively
  • Engagement (Obstetrics)
    • When the widest transverse diameter of the head (presenting part) passes through the pelvic inlet
    • Use the rule of fifths: engagement is clinically identified when ≤ 2/5 of the fetal head are felt above the symphysis pubis through the maternal abdomen

Synclitism

  • Definition: parallelism between the pelvic plane and the plane of the fetal head
  • In asynclitism, the sagittal suture is in the transverse diameter of the pelvic inlet and not between the symphysis pubis and sacral promontory.
    • Anterior asynclitism (Naegele obliquity)
      • The sagittal suture is positioned towards the sacral promontory
      • Spontaneous vaginal delivery possible
    • Posterior asynclitism (Litzmann obliquity)

Obstetric contractions (uterine muscle contractions) [3][4][5]

Overview of obstetric contractions [1][6][7]
Time Characteristics

Uterine contractions during pregnancy

Alvarez-waves
  • Physiological; occurs after 20 weeks of pregnancy
  • Low intensity, high frequency
Braxton Hicks contractions (false labor)
  • Irregular, uncoordinated uterine contractions of moderate intensity (helps with fetal positioning)
  • Frequency: typically ≤ 2 times/hour
  • Duration: ≤ 1 minute
  • Do not increase in frequency, intensity, or duration.
  • Cervical changes are absent
  • Typically stop with rest, walking, and/or a change in position.
Prelabor
  • 3–4 days before birth
  • Irregular contractions of high intensity, which occur every 5–10 min shortly before phase 1 begins. They are responsible for correctly positioning the fetal head in the pelvis.
Labor Stage 1: cervical dilation and effacement
  • Coordinated, regular, rhythmic contractions of high intensity; occur approximately every 10 minutes. Shortly before stage 2, they occur every 2–3 min. These contractions are responsible for cervical dilation.
Stage 2: fetal expulsion
  • Coordinated and regular contractions of high intensity; occur approximately every 4–10 min and are responsible for fetal expulsion. Towards the end of the stage, they occur very often (every 2–3 minutes) and are of higher intensity (≥ 200 Montevideo units).
Stage 3: placental expulsion or afterbirth
  • Irregular contractions of very low intensity, which force the placenta through the vaginal canal within 30 min after fetal expulsion
Afterpains
  • Irregular contractions of varying intensity, which cause uterine involution and bleeding cessation

False labor only requires reassurance.

Rupture of membranes (ROM)

Stages of labor [3][4][5]

Overview of the stages of labor
Stage Characteristics Duration Clinical features
Nulliparous patients Multiparous patients
First stage of labor Latent phase of labor
  • Occurs during the onset of labor and ends at 6 cm of cervical dilation [8]
  • Characterized by mild, infrequent, irregular contractions with a gradual change in cervical dilation (< 1 cm/hour) [9]
  • ≤ 20 hours
  • ≤ 14 hours
Active phase of labor
Second stage of labor
  • < 2 hours (< 3 hours in patients who received an epidural)
  • < 1 hour (< 2 hours in patients who received an epidural)
  • Completely dilated cervix
  • Regular uterine contractions increasing in frequency and intensity
  • Crowning: the appearance of the fetus's head at the vaginal opening as contractions progress
Third stage of labor
  • 30 minutes
  • Uterine contractions (to expel the placenta)
  • Signs of placental separation
    • Cord lengthening
    • Gush of vaginal blood (usually accompanied by a blood loss of 300 mL)
    • Uterine fundal rebound (the uterus becomes less elongated and more spherical)
Fourth stage of labor
  • N/A
  • Uterine contractions
  • Expulsion of any remaining contents

Management of labor by stage

Normal mechanics of childbirth [1]

Adaptation to the different forms of the pelvic region requires a great deal of rotation.

  1. Engagement, descent, and increased flexion (occur simultaneously)
    • The head engages below the plane of the pelvic inlet.
    • The presenting part begins to descend into the birth canal.
    • The chin of the fetus moves towards its chest.
  2. Internal rotation: The fetal head rotates by 90° (two 45° steps) in the midpelvis, from a transverse to anterior-posterior position.
  3. Extension: The fetal head, lying behind the symphysis pubis bone and the pelvic floor, acts upwards and forwards.
  4. Restitution: The fetal head rotates 45° in the opposite direction as it passes through the pelvic outlet.
  5. External rotation: The anterior shoulder rotates 45° anteriorly as it meets the maternal pelvic floor. This action is transmitted to the head which also rotates 45°, placing the head in its original transverse position.
  6. Expulsion: Delivery of the head, anterior shoulder followed by the posterior shoulder, and the body

Electronic fetal heart rate monitoring [12][13]

Fetal heart rate [14][15][16]

Fetal heart rate (FHR) tracing

Fetal heart rate tracing categories
Category I FHR tracing Category II FHR tracing Category III FHR tracing
Characteristics
  • Includes all FHR measurement outside category I FHR tracings (normal) or category III FHR tracings (abnormal)
  • May progress to normal or abnormal

Interpretation

Management

  • No interventions necessary
  • Surveillance and frequent reassessment until category II FHR tracings resolve (category I FHR tracings) or progress (category III FHR tracings)

Fetal heart rate variability [17]

On CTG, variability of FHR is represented by the oscillation of the FHR around the baseline and is determined by measuring the amplitude between the highest and lowest turning point of the FHR curve.

Overview of fetal heart rate variability
Type Oscillation amplitude Causes
Moderate variability
  • 6–25 bpm
  • Physiological fluctuation of FHR
  • Normal finding
Absent variability
  • Undetectable amplitude
Minimal variability
  • < 6 bpm
Marked variability
  • > 25 bpm
Sinusoidal variability
  • 5–15 bpm
  • FHR wave resembles a sinus wave
Pseudosinosoidal variability
  • Similar appearance to sinusoidal variability
  • Irregularly shape and amplitude of the FHR curves

Acceleration (CTG) [16]

  • Description: a normal temporal increase in the FHR from the baseline by > 15 bpm for more than 15 seconds but less than 10 minutes if the gestational age is > 32 weeks, or by > 10 bpm for more than 10 seconds if the gestational age is < 32 weeks
  • Interpretation

Decelerations (CTG) [12][18][19][20][21]

  • Description: a temporary decline in the FHR of > 15 bpm for a maximum duration of 3 minutes
Overview of types of fetal deceleration
Type Etiology Characteristics Measures

Early deceleration

  • Compression of the head during a contraction triggering a vagal response
  • The beginning and end of decelerations correspond with the progression of a contraction (the deceleration reaches its minimum, referred to as the nadir, when the contraction curve attains its peak).
  • Onset to nadir is gradual (≥ 30 seconds).
  • Typically occurs during active labor when the cervix is dilated ≥ 5 cm and the head is engaged within the pelvic cavity
Late deceleration
  • Decrease in the FHR following the maximum contraction curve
  • Onset to nadir is gradual (≥ 30 seconds).
Variable deceleration
  • Variable presentation and temporal relation to the changes in contractions
  • Onset to nadir is abrupt (< 30 seconds) and lasts ≥ 15 seconds but < 2 minutes.
Prolonged deceleration
  • A decrease in FHR of ≥ 15 bpm from the baseline, lasting ≥ 2 minutes but < 10 minutes

Consider umbilical cord compression or umbilical cord prolapse in patients with recurrent variable decelerations (≥ 50% of contractions).

MNEMONIC for etiology of fetal HR alterations: VEAL CHOP
Variable decelerations → Cord compression/prolapse
Early decelerations → Head compression
Accelerations → OK
Late decelerations Placental insufficiency/Problem

Interpretation

Management

See “Intrauterine resuscitation” for details.

Perineal lacerations

Complications of fourth-degree lacerations include rectovaginal fistulae.

Obstetric nerve injuries [29]

Acute nerve injury can occur during childbirth due to compression, transection, traction, or vascular injury to the nerve.

Obstetric nerve injuries
Nerve Clinical features Risk factors
Lumbar radiculopathy
Lateral femoral cutaneous nerve injury
Femoral nerve injury
Common peroneal nerve injury
  • Prolonged squatting during childbirth
  • Hyperflexion of the knees during childbirth
  • Direct compression of the nerve with direct pressure over the fibular head
  • Inadequate footrests or stirrups used during vaginal delivery
Pudendal nerve injury

Coccydynia

  • Etiology: injury to the coccyx during childbirth as a result of internal and external pressure on the coccyx during labor and delivery
  • Clinical features
    • Pain and tenderness of the coccyx, esp. when sitting or leaning back
    • Pain may suddenly increase when the patient is changing from a sitting to a standing position.
    • Pain may also occur during defecation or sexual intercourse.
    • Physical examination: palpation of the coccyx elicits pain
  • Diagnosis: clinical
  • Management
    • Protection (e.g., sitting on Donut or wedge cushions)
    • Analgesics (e.g., NSAIDs)
    • Local heat or cooling according to patient preference
    • Exacerbating factors (e.g., sitting on hard surfaces, cycling) should be avoided if possible.
  • Prognosis: resolves spontaneously in the majority of patients (> 90%) [30]

Postpartum retroperitoneal hematoma

  • Statistics
    • In the US, approx. 1% of births per year are home births.
    • 75% of these home births are planned.
  • Indications
    • There is insufficient evidence to determine what makes a good candidate for a home birth.
    • Home births can be considered in individuals with no contraindications.
    • Patients who would like to plan a home birth should be advised about the benefits and risks of home birth compared to hospital delivery in order to make an informed decision.
  • Advantages compared to hospital delivery
  • Disadvantages compared to hospital delivery
    • Higher risk of perinatal death for both the mother and fetus
    • Higher risk of neurological complications for the newborn
  • Contraindications

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