Labour Mechanism and Physiology Flashcards
Causes of failure to progress in labour?
- Related to the powers = inefficient uterine action
- Related to the passenger = foetal size; disorder of rotation (occipito-transverse, occipito-posterior positions etc.); Disorder of flexion (e.g. brow presentation)
- Disorders of the passage; cephalo-pelvic disproportion or possible role of cervix
Maternal risk factors for failure to progress in labour?
- Pelvic inflammation
- Pelvic tumour / fibroid
- Arcuate or septate uterus
- Oligohydraminos
- Placenta praevia
- Laxity of muscular layer in walls of uterus
What is an arcuate uterus?
Uterine cavity displays a concave contour towards the fundus
What is a septate uterus?
septum divides the inner portion of the uterus at its midline
Foetal RFx for failure to progress in labour?
o Prematurity
o Multiple pregnancy
o Foetal malformation e.g. hydrocephalus
o Intrauterine deaths
Mx of women with inefficient uterine contractions?
o Encourage mobility and supportive measures
o Persistently slow progress is Tx by augmentation (artificial strengthening of contractions); a) Initially with amniotomy (deliberately rupturing amniotic sac)
b) If this does not work in dilating cervix after 2 hours, then oxytocin is given, after malpresentation has been excluded
Mx of foetuses that are malpresenting?
o Rotations OP baby to OA using ventouse or manual rotation
o OT delivered using a ventouse
o Brow presentation = c-section
o Face presentation = c-section
What is cervical ripening?
- This describes the process by which the cervix goes from a closed, firm structure to a softer, thinner one that opens up adequately for birth
- Occurs before the onset of labour, in the weeks/days predating labour
- It is a more accelerated phase characterised by maximal loss of tissue compliance and integrity
- Upon initiation of uterine contractions, the ripened cervix can dilate sufficiently to allow passage of the foetus
- Effacement is when the normally tubular cervix (like a long bottleneck, up to 4cm in length) is drawn up into the lower segment until it is flat (loss of collagen and elastic tissues)
Where are the pacemakers of the uterus?
In the cornu
What are the phases of labour?
- Stage 1 (made up of latent and active stages)
- Stage 2
- Stage 3
What is the latent phase of labour?
When the cervix dilates up to 3cm
What is the active phase of labour?
From 3 to 10cm (fully) dilated
What is the average rate of dilation in the active phase?
0.5cm/hour for nulliparous women or 1cm/hour for multiparous women
What happens in the 2nd stage of labour?
From full dilatation of the cervix to delivery of the foetus
What happens in the 3rd stage of labour?
From delivery of the baby to delivery of the placenta
How long does the 2nd stage usually take?
40 mins for nulliparous women, 20 mins for multiparous women (>1 hour makes spontaneous labour less likely)
What are the mechanisms that occur in labour?
- Descent into the pelvis (baby is in transverse position to get through the pelvic inlet)
- Flexion of the baby (should be fully flexed, with the chin down to the body)
- Internal rotation (foetal head turns towards the posterior wall as it reaches the pelvic floor)
- Extension (the foetal head extends beneath the suprapubic arch allowing the head to be born)
- Restitution / external rotation (the head turns back to the transverse position once it is outside of the woman, so that it is back in line with the rest of the body, allowing this to be born)
What are the 3 factors that are key participants in labour?
- Powers = the degree of force expelling the foetus
- The passage = the dimensions of the pelvis and the resistance of the soft tissues
- The passenger = diameters of the foetal head
In active labour, how much does the uterus contract?
45-60 seconds about every 2-4 minutes
What is the bregma?
The anterior fontanelle, (above the forehead)
What is the occiput?
The posterior fontanelle (on the back of the top of the head)
What is moulding?
Head can be compressed in the pelvis because sutures allow the bones to come together and even overlap slightly
What is a partogram?
- Partogram is used to record progress in dilatation of cervix and descent of the head
- Assessed on vaginal examination and plotted against time
- After the latent phase (i.e. >4cm dilated), usual minimum rate of dilatation is 1cm/hour
- Also monitor foetal heart rate (for foetal distress), maternal pulse, BP and temperature
What is foetal distress?
Foetal hypoxia that might result in foetal damage or death if not reversed or the foetus delivered urgently
What are the maternal consequences of failure to progress in labour?
- Higher chance of operative delivery
- Infection of uterus
- Damage to birth canal
- Postpartum infection
- Postpartum haemorrhage
What is the normal position for labour?
Vertex position. Highest part of foetal head arrives at the pelvic brim first. Chin is tucked down into chest. Occipito-anterior position, when back of babies skull points to the pubic symphysis. 95% occur this way.
What is a breech position?
Foetus lies with buttocks in lower part of uterus and its buttocks and/or feet are the presenting parts during delivery. 3-4% after 34 weeks (at term). 25% before 34 weeks
Can breech position be delivered normally?
Yes; but it is higher risk
RFx for breech position?
- Obstructive placenta
- Multiple pregnancy
- Premature labour (baby may not have turned yet)
- Polyhydraminos (nothing to hold the baby in face)
- Abnormal uterus formation
- Hydrocephaly
What are the 3 types of breech?
- Complete breech (baby is sitting, legs flexed)
- Frank breech (baby is doubled up on itself; legs extended)
- Footling breech (one of both of legs hanging down; baby is stood up)
How to turn the baby around when breech?
Turn the baby using ECV by pressing on the abdominal wall
What happens in a face presentation?
baby’s neck is so completely extended that the occiput at the back of the foetal skull touches baby’s own spine. Chin will present first. 1 in 500 pregnancies. Also called a mento-anterior or mento-posterior (mentum is chin bone). Anterior can be delivered vaginally, but not posterior
What is a brow presentation?
baby’s head only partially extended at neck, so brow is presenting part. 1 in 1000 pregnancies. Must be delivered by c-section
What is meconium?
Amniotic fluid stained with babies’ faeces
Is meconium worrying?
Can be a sign of foetal distress if very thick, but can be fine. Not worrying at all in breech position
Initial Mx of a woman that fails to progress in labour?
- ABC, hydration, pulse, ketotic state
- Abdo exam (check for breech position)
- Vaginal exam (confirm dilatation, see how high head is, rotation of head, cervical dilatation for obstructed labour, head compression)
- Analgesia
- Can artificially rupture membrane
Which factors influence mode of delivery?
- Maternal distress
- Foetal distress
- Obstruction
