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creation date: 2025-07-27 19:01
tags: Anatomy & Physiology

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Labour and Delivery

Pre-labour

Initial phase of childbirth which involves:

• Cervix softening, shortening, opening
• Irregular contractions that can be mild or painful

This phase can last from a few hours to several days.

In approximately 10% of pregnancies, the membranes surrounding the fetus may rupture prior to onset of labour. This is referred to as premature rupture of membranes (PROM) if it occurs >18 hours prior to labour and increases risk of maternal and fetal infection.

PROM is characterized by a gush or leak of fluid from the vagina which can be confirmed with the pool, nitrazine, and fern tests. Note that stress incontinence and small leaks of amniotic fluid does not constitute PROM diagnosis.

Prodromal labour or “false labour” is diagnosed with irregular contractions that have little or no cervical change. The patient is not diagnosed as in labour until contractions are regular and yield cervical change.

Induction of labour

Induction refers to the attempt to begin labour in a non-labouring patient.

The indication of labour depends on maternal, fetal, and fetoplacental factors and includes conditions such as preeclampsia, non-reassuring fetal testing, and intrauterine growth restriction.

Induction consist of some combination of:

• Prostaglandins (eg. misoprostol) for cervical ripening
• Mechanical dilation of the cervix (using Foley bulb to pressure inside of cervix)
• Oxytocic agents to induce contractions
• Artificial rupture of membrane

The success of an induction is more likely with favourable cervical status as defined by the Bishop score (discussed below) and a score ≤5 is associated with a failure rate of as high as 50%.

Labour

Obstetric and cervical examination

Examinations are done to assess whether the patient is in labour, which phase of labour, and how labour is progressing.

The physical exam begins with determination of fetal lie using the Leopold maneuvers which involves palpating the fundus, then sides of the uterus, then the presenting part just above the pubic symphysis. This is not always reliable especially if the patient is obese.

There are five components of the cervical exam which make up the Bishop score:

• Dilation: diameter at internal os of cervix, in cm
• Effacement: subjective measure of % effaced the cervix is (non-effaced is 3-5cm)
• Fetal station: relation of the fetal head to the ischial spine of the pelvis (0 refers to the exact level of the ichial spine, + is above, - is below)
• Cervical position: position from posterior to anterior
• Consistency of the cervix: ranges from firm to soft

The Bishop score, sums each component:

Score	0	1	2	3
Diltation (cm)	Closed	1-2	3-4	>5
Effacement (%)	0-30	40-50	60-70	>80
Station	-3	-2	-1, 0	>+1
Consistency	Firm	Medium	Soft
Position	Posterior	Mid	Anterior

As labour progresses, the state of each component moves from 0 to 3. A score of >8 is generally considered favourable for both spontaneous and induced labour.

Note that if the fetal lie was not determined or was inconclusive using the Leopold maneuvers, it can be confirmed during cervical examination by palpation and/or by ultrasound.

Ultrasound may also determine fetal position in vertex position:

• Occiput anterior (OA) - most favourable; “fetus facing the spine”
• Occiput posterior (OP)
• Occiput transverse (OT)

Fetal monitoring

Fetal monitoring consist of determination of baseline heart rate and variations with contractions.

Continuous fetal heart monitoring are the standard as they are easily monitored by nursing staff and provide easy data collecting but requires the mother to have an electronic fetal monitor strapped to them which can limit mobility and comfort.

Additionally, an external tocometer with a pressure transducer is used to record contraction pressure through abdomen firmness which can provide information on the frequency of contraction and the fetal heart rate changes relative to contractions.

In low risk pregnancies, intermittent monitoring, using auscultation or doppler, may be preferred with no difference in complications/risks.

In cases of concerning findings on normal monitoring or if external monitoring is unreliable, a fetal scalp electrode can be used. Scalp pH from a blood draw may also be used when heart tracing is nonreassuring.

Fetal heart rate evaluation

Fetal heart rate and changes provide information on the state of the fetus.

The normal range is 110-160 bpm. A fetal heart rate variability (beat-to-beat variation) should be present unless the fetus is asleep or inactive and is defined as:

• Absent (<3 beats per minute of variation)
• Minimal (3-5 beats per minute of variation)
• Moderate (5-25 beats per minute of variation)
• Marked (>25 beats per minute of variation)

Accelerations are a sign of reactivity and is a reassuring sign.

Decelerations are seen in the tracing and should be examined with the tocometer to determine the type and severity:

• Early deceleration (beginning and ends at same time as contractions) - due to increased vagal tone secondary to head compression and generally benign
• Variable deceleration (occurs at any time and drop precipitously) - due to umbilical cord compression; repetitive variables with contractions may be due to cord around neck or shoulder being compressed with contraction
• Late decelerations (begins at contraction peak and returns to baseline after contraction ends) - due to uteroplacental insufficiency and are ominous; may degrade to bradycardias with stronger contractions

These findings are summarized by the mnemonic VEAL CHOP:

• Variable - Cord
• Early - Head compression
• Acceleration - Okay
• Late - Placenta

Pain management

Pain during labour can cause hyperventilation and increased catecholamine levels which may be problematic with patients with comorbidity.

Non-pharmacological

The evidence for non-pharmacological pain relief is not concrete but generally is not harmful.

Common options include:

• Breathing techniques for relaxation and focus during contractions
• Position changes
• Water therapy
• Massage/touch
• Heat and cold application
• Support from family, friend, partner, and/or doula

Pharmacological

Locoregional

The most effective form of pain management are neuraxial analgesia. This can be epidural, spinal, or combined spinal-epidural.

Epidurals are typically given in stage 1 of labour at L3-L4 as patient must be able to stay still and time required for it to work. Maternal blood pressure is monitored q2-5 mins for 15-20 mins and regularly after.

Spinal blocks have a more immediate/shorter effect and is typically used for caesareans. The block is applied at L3-L4 but there is risk of the anesthesia travelling superiorly in the subdural space to the brainstem causing respiratory arrest.

Local anesthesia for target numbing may be used especially for episiotomy or repair of lacerations. A pudendal block, injected into the vaginal wall, may be injected during stage 2 to numb the perineum for delivery.

Systemic

Opioids may be used, particularly during stage 1. Generally not used in later stages due to the sedative effect. Opioids may also pass through the placenta and cause respiratory depression in the baby.

Nitrous oxide may also be used with no accumulation in the mother or fetus.

Note, acetaminophen and NSAIDs are contraindicated due to the risk of premature closure of the ductus arteriosis in the fetus.

Augmentation of labour

Pitocin (synthetic oxytocin) and amniotomy can be used to augment labour. This is typically indicated if contractions are inadequate or if a phase of labour is prolonged.

Adequacy of contractions is assessed by progress of cervical change but can also be measured by an intrauterine pressure catheter.

Progression (cardinal movements) of labour

In addition to the progression of cervix, the descent of the fetus is used to gauge the progress of labour.

1. Engagement: the fetus’ presenting part enters the pelvis
2. Descent: the head descends into the pelvis
3. Flexion: fetal chin is pushed against the chest which allows for smallest possible diameter
4. Internal rotation: the fetus moves from an OT position to an OA position (improper rotation results in maintaining OT or malrotation to OP)
5. Extension: as the fetus passes the pubic symphysis, the neck extends to deliver
6. External rotation: once the head is delivered, the rest of the body externally rotates so the shoulders can be delivered
7. Expulsion: the shoulders and body follows to be delivered

Stages

Stage 1

Onset of labour until dilation and effacement are completed. This stage on average last 10-12 hours in a nulliparous patient (range: 6-20 hrs) and 6-8 hours in a multiparous patient (range: 2-12 hrs).

Latent phase

This phase ranges from onset of labour until approximately 3-4 cm of dilation.

• Regular contractions
• Slow cervical changes

Active phase

This phase follows the latent phase and extends until great than 9cm of dilation.

• Rate of cervical change increases
• In nulliparous patients, dilation expected to be >1.0 cm/hr
• In multiparous patients, dilation expected to be >1.2 cm/hr

The transit time is based on the 3 P’s - power, passenger, pelvis - and should be assessed if dilation rate drops below 1 cm/hr for possible cesarean section delivery.

• Cephalopelvic disproportion refers to a fetus (passenger) that is too large for the pelvis
• Inadequate contractions as determined by an intrauterine pressure catheter measurement <200 Montevideo units

Stage 2

Time of full dilation until delivery. This phase is considered prolonged if:

• Nulliparous and >2 hours; or >3 hours with an epidural
• Multiparous and >1 hour; or >2 hours with an epidural

The variation in duration depend on the position of the fetus, size, and contractions. Epidurals may slow down this stage due to the block resulting in less urge to push.

Management varies for this stage but may include a “labouring down or passive descent” stage in which the patient does not push. Evidence does not suggest a difference in outcomes whether the stage is prolonged or not.

Note that at this phase, repetitive early and variable decelerations often occur and are generally non-concerning if they resolve quickly after contraction.

Repetitive late decelerations, bradycardias, and loss of variability are not reassuring and patient should be placed on mask O2 and turned to the left to reduce IVC compression. Nonresolving decelerations may require cesarean delivery or operative vaginal delivery depending on station.

Delivery

Vaginal delivery

As the fetus is crowning the clinician should don:

• Eye protection
• Sterile gown
• Sterile gloves
  and have:
• Two clamps
• Scissors
• Suction bulb

The generally used approach is to take a smooth, controlled delivery:

• One hand on the perineum
• One hand to flex the head to keep it from extending too rapidly

In situations where the delivery needs to be expedited, a modified Ritgen maneuver can be used, albeit at the risk of greater perineal lacerations:

• Heel of bottom hand exerts pressure on the perineum
• Fingers below the anus exerts pressure on the fetal chin to extend the head

Once the head is delivered, the mouth and upper airway are bulb suctioned and the infant’s neck is checked for nuchal cord. If a nuchal cord is present and is unable to be reduced, the clinician can:

• Clamp and cut the cord if the clinician is confident the livery will be accomplished shortly
• Attempt delivery with nuchal cord if a shoulder dystocia is suspected

Delivery of the rest of the infant follows:

1. Exert downward pressure to deliver the anterior shoulder
2. Exert upward pressure to deliver the posterior shoulder
3. Gentle traction to deliver the torso and rest of infant

If it hasn’t been done, the cord is then clamped and cut. Note, episiotomies are not routine for vaginal delivery.

Operative vaginal delivery

In cases of a prolonged second stage, maternal exhaustion, or need to expedite, operative vaginal delivery using either forceps or vacuum-assist may be indicated. Safe conditions require:

• Full dilation of cervix
• Ruptured membrane
• Engaged dead with at least +2 station
• Absolute knowledge of fetal position
• No evidence of CPD
• Adequate anesthesia
• Empty bladder
• Experienced operator

Forceps delivery involves placing the curved blades of the forceps around the fetal head to guide the fetus and aid expulsive efforts through the pelvis.

Vacuum extraction involves placing a vacuum cup to the fetal scalp and a suction device used to aid expulsion.

Stage 3

Following delivery of the infant until delivery of the placenta.

Following the birth of the infant, immediate skin-to-skin contact is indicated for at least an hour, although the longer the more beneficial.

Placental separation usually occurs within 5-10 minutes of infant delivery but up to 30 minutes is considered normal.

The abrupt decreased of intrauterine cavity size mechanically shears the placenta off the wall with the aid of contractions. The use of oxytocin can also aid placental delivery as long as there is no doubts of an undiagnosed twin (typically confirmed with ultrasound).

Signs of placental separation include:

• Cord lengthening
• Gush of blood
• Uterine fundal rebound
  and gentle traction on the cord can be applied once all three signs are noted. Forceful traction should be avoided and suprapubic pressure applied to prevent uterine inversion or prolapse.

Manual extraction may be required if the placenta does not detached within 30 minutes or if components are retained (placenta accreta).

Post-partum

Neonatal assessment

Immediately following delivery, the neonate is assessed using the APGAR score:

Sign	0	1	2
Appearance	Blue and/or pale	Pink body, blue limbs	Pink
Pulse	Absent	<100 bpm	>100 bpm
Grimace	No response	Grimace	Coughing and crying
Activity	Limp	Weak	Strong
Respiration	Absent	Irregular, slow	Good, crying

A score of ≥7 is reassuring. This is done immediately after birth and 5 minutes post-delivery. If the infant scores <7 at 5 minutes, scores will be checked at five-minute intervals for 20 minutes. Resuscitative efforts may be necessary for low scores.

Other tests done include:

• Dried blood spot (eg. for blood type, metabolic/endocrine disease, hemoglobinopathies, cystic fibrosis)
• Critical Congenital Heart Disease (CCHD) testing via pulse oximetry
• Hearing test (can be post-discharge too)

Maternal assessment and recovery

Thorough examination of the perineum, labia, periurethral area, vagina, anus, and cervix is performed and lacerations are repaired.

Assessment for complication includes uterine rupture and post-partum hemorrhage.

Discharge

Discharge is typically indicated following:

• Stable vitals for >12 hours
• Evidence of stooling and urination
• Two successful feedings
• No need for continued care
• No excessive bleeding
• Family is trained for care