Labour Flashcards
What is labour?
The process whereby the fetus and placenta expelled from the uterus, which normally occurs between 37 and 42 weeks.
When is labour diagnosed?
When painful uterine contractions accompany dilatation and effacement of the cervix
What occurs in the first stage of labour?
The cervix opens to full dilatation to allow the head to pass through
When is the second stage of labour?
Between full dilation and the delivery of the fetus
What is the third stage of labour?
From delivery of the fetus to delivery of the placenta
What are the three mechanical factors of labour?
[1] The degree of force expelling the fetus (the powers)
[2] The dimensions of the pelvis and the resistance of soft tissues (the passage)
[3] The diameters of the fetal head (the passenger)
How often does the uterus contract during labour?
For 45-60 seconds about every 2-3 minutes
What do contractions do?
Pull the cervix up (effacement) and cause dilation, aided by the pressure of the head as the uterus pushes the head down into the pelvis.
When is poor uterine activity common?
In nulliparous women and in induced labour
How is the level of descent in the uterus measured?
Using the ischial spines as station 0 and how many cm above or below, if it is 2cm below the spines, it is station +2, if it is 2cm above the spines it is station -2.
What factors determine how easily the head fits through the pelvic diameters?
The attitude (extension/flexion); the position (rotation) and the size of the head
What attitude is ideal for labour?
Maximal flexion, keeping the head bowed, this is called vertex presentation.
Why do you not want the attitude to be extension in labour?
A small degree of extension results in a larger diameter.
What is a brow presentation?
Extension of the head at 90 degrees
What is a face presentation?
120 degree extension of the head, with the face looking parallel and away from the body.
What is the position of the head?
The degree of rotation of the head on the neck.
What should happen to the position of the head during labour?
The head must normally rotate 90 degrees during labour to fit through. It should be delivered with the occiput anterior.
What is moulding?
The head can be compressed in the pelvis because the sutures allow the bones to compress together and even overlap slightly
What are the positions that the head can be in?
Occipito-transverse (bad, needs assistance)
Occipito-posterior (more difficult to deliver)
Occipito-anterior (good)
What does prostaglandin production do during pregnancy?
It reduces cervical resistance and increases the release of oxytocin from the posterior pituitary, which aids stimulation of contractions
What is effacement?
When the normal tubular cervix is drawn up into the lower segment until it is flat.
What is the ‘show’ that often accompanies effacement?
Pink/white mucus plug from the cervix and/or rupture of the membranes, causing release of liquor.
What is the latent phase of the first stage of labour?
Where the cervix usually dilates slowly for the first 4 cm and may take several hours
What is the active phase of the first stage of labour?
When the cervix dilates from 5 cm to full (10 cm). Average cervical dilatation is at the rate of 1cm/h in nulliparous women and about 2cm/h in multiparous women. The active first stage should not normally last more than 12h
What happens to the fetus during the second stage of labour?
Descent, flexion and rotation are completed and followed by extension as the head delivers.
What is the passive stage of the second stage of labour?
It is from full dilatation until the head reaches the pelvic floor and the woman experiences the desire to push.
How long does the passive stage of the second stage of labour last?
It can last a few minutes, but can be much longer
What is the active stage of the second stage of labour?
When the mother is pushing.
What causes the urge for the mother to push?
The pressure of the head on the pelvic floor produces an irresistible desire to bear down, although epidural analgesia may prevent this.
How long after the active stage of the second stage of labour is the baby normally delivered?
On average after 40 minutes (nulliparous) or 20 minutes (multiparous). This can be much quicker but if it is over an hour spontaneous delivery is unlikely
How long does the third stage of labour usually last for?
15 minutes
Why does the mother stop bleeding after delivery?
Uterine muscle fires contract to compress the blood vessels formerly supplying the placenta, which shears away from the uterine wall.
What is a first degree perineal tear?
Involves minor damage to the fourchette.
What is a second degree perineal tear?
Tear involving perineal muscle
What is a third degree perineal tear?
Tear involving the anal sphincter.
What is a fourth degree perineal tear?
Tear involving the anal mucosa
How can you reduce a woman fear of labour?
Information, reassurance, accommodating reasonable wishes and, most importantly, not treating labour as a disease
Why is fear during labour bad?
Fear leads to adrenaline secretion and adrenaline is a potent inhibitor of uterine contractions.
What position should pregnant women in labour NOT be in?
Flat on their back
Are women allowed to eat in labour?
It should be discouraged in case general anaesthetic is needed.
What observations are taken during labour?
Temperature, pulse and blood pressure
What is a partogram?
A growth chart-like thing that monitors the dilatation of the cervix ±descent of the head over time. Also records maternal vital signs, fetal heart rate and liquor colour
What is hyperactive uterine action?
Excessively strong or frequent or prolonged contractions.
What is the complication of hyperactive uterine action and why does it happen?
Fetal distress occurs as placental blood flow is diminished and labour may be very rapid.
How long does it take for oxytocin to work?
Oxytocin should increase cervical dilatation within 4h if it is going to be effective.
What is augmentation?
The artificial strengthening of contractions in established labour.
What are the clinical features of occipital-posterior position?
Labour is often longer and more painful, with backache and an early desire to push.
What are the common causes of failure to progress in labour?
Powers: inefficient uterine activity
Passenger: fetal size; disorder of rotation; disorder of flexion
Passage: cephalic-pelvic disproportion; possible role of cervix
What is cephalic-pelvic disproportion?
The pelvis is simply too small to allow the head to pass through. It is often diagnosed retrospectively after exclusion of other reasons for failure to progress.
What are the risk factors for cephalic-pelvic disproportion?
Large baby, small woman, high head at term in nulliparous women
How do you measure fetal hypoxia?
The convention is that a pH below 7.2 in the scalp (capillary) blood indicates significant hypoxia but only below 7.0 can cause neurological damage.
What length of labour can increase the risk of hypoxia and why?
Contractions temporarily reduce placental perfusion and may compress the umbilical cord, so longer labours and those with excessive time (>1h) spent pushing
What are some complications that can cause fetal hypoxia?
Placental abruption, hypertonic uterine states and the use of oxytocin, prolapse of the umbilical cord and maternal hypotension
What are some risk factors for fetal hypoxia?
Long labour, meconium, the use of epidurals and oxytocin; PE, IUGR.
What are some investigations that are used to diagnose fetal hypoxia?
Colour of the liquor (meconium); fetal heart rate auscultation; CTG; fetal ECG monitoring; fetal blood (scalp) sampling
What is meconium?
The bowel contents of the fetus that stains the amniotic fluid
In what gestation delivery is meconium more common?
It is rare in preterm foetuses but common after 41 weeks
What does meconium mean?
When very diluted it is seldom significant; with undiluted (pea soup) perinatal mortality is increased fourfold.
How often is the fetal heart rate auscultated?
Every 15 minutes during the first stage and every 5 minutes in the second, with a hand-held Doppler for 60 seconds after every contraction
What is the mnemonic for assessing a CTG?
Dr: define risk C: contractions per 10 minutes Bra: baseline rate (110-160 beats/minute) v: variability (>5beats/minute) a: accelerations (reassuring) d: decelerations o: over assessment
What are the types of decelerations?
Early decelerations, variable decelerations, late decelerations
What are early decelerations?
Synchronous with a contraction as a normal response to head compression and are therefore usually benign
What are variable decelerations?
Independent of contractions and classically reflect cord compression, which can ultimately cause hypoxia
What are late decelerations?
They persist after the contraction is completed and are suggestive of fetal hypoxia
Are CTG’s accurate?
A normal CTG is reassuring but the false-positive rate of abnormal patterns is high, do fetal scalp pH before intervention except in emergencies
How do you manage fetal hypoxia?
Reposition woman (on left side), oxygen and IV fluids administered; stop oxytocin; vaginal examination
Why is meconium bad?
It can be aspirated by the fetus into its lungs, where it can cause severe pneumonitis
What are the anaesthesia options for obstetric procedures?
Spinal anaesthesia; pudendal nerve block; epidural analgesia.
What are the risk factors for third and fourth degree tears?
Forceps delivery, large babies, nulliparity.
What are the criteria for a home birth?
Woman's request 'Low risk' 37-41 weeks Cephalic presentation Clear liquor Normal fetal heart rate
What score is used to assess the need for induction?
Bishops score. The lower the score the more unfavourable the cervix
What are the features of Bishop score?
- Cervical dilation
- Cervical effacement
- Cervical position
- Cervical consistency
- Fetal position
A score of < 5 indicates that labour is unlikely to start without induction
A score of > 9 indicates that labour will most likely commence spontaneously
What are the methods of induction?
Medical: prostaglandins; oxytocin (after membrane rupture)
Surgical: amniotomy
What do prostaglandins do?
It either starts labour, or the ‘ripeness’ of the cervix is improved to allow amniotomy.
When are prostaglandins most effective?
In the evening
What is cervical sweeping?
Passing a finger through the cervix and ‘stripping’ between the membranes and the lower segment of the uterus
What are some fetal indications for induction?
High risk situations such as prolonged pregnancy, suspected IUGR or APH, poor obstetric history and prelabour preterm rupture of the membranes
What are some materno-fetal indications for induction?
PE, maternal diabetes
What are some contraindications of induction?
Acute fetal compromise, abnormal lie, placenta praevia or pelvic obstruction such as a pelvic mass or pelvic deformity, previous C section.
What are the complications of induction?
Labour may not start, increased risk of instrumental delivery and C section. Over activity of the uterus; PPH
What are some factors that increase the chance of successful vaginal delivery after a C section?
Spontaneous labour; <2 yrs interpregnancy interval; low age and BMI; Caucasian; previous elective C section or vaginal delivery; small fetus
How do you diagnose prelabour preterm rupture of the membranes?
Typically, there is a gush of clear fluid, which is followed by an uncontrollable intermittent trickle.
What are the risks of prelabour preterm rupture of the membranes?
Cord prolapse is rare; small but definite risk of neonatal infection, which is increased by vaginal examination, the presence of group B strep and increased duration of membrane rupture
What are the main causes of fetal distress?
Fetal hypoxia Infection (strep B) Meconium aspiration (pneumonitis) Trauma (forceps) Fetal blood loss
