What is labour?
The physiological process by which a fetus is expelled from the uterus to the outside world
What does the process of labour involve?
The sequential integrated changes in uterine decidua, and myometrium
What tends to precede uterine contractions in labour?
Changes in the uterine cervix
How do Braxton-Hicks contractions differ from labour?
They do not cause the cervix to dilate
What are the two main goals of uterine contractions in labour?
- Dilate cervix
- Push fetus through birth canal
What are the three P's of labour problems?
What effect does the oestrogen/progesterone ratio have on the uterine musculature in labour?
It changes to increase excitability
What effect does progesterone have on the uterine musculature in labour?
It inhibits contraction by reducing the excitability of muscles
What effect does oestrogen have on the uterine musculature in labour?
Increases gap junctional communication between smooth muscle cells, increasing contractility
What effect does oxytocin have on uterine musculature during labour?
Where is oxytocin secreted from?
Maternal posteiror pituitary gland
What effect does mechanically stretching uterine smooth muscle in labour have?
What does cervical stretching elicit in labour?
How do fetal effects contribute to labour?
- Fetus produces hormones which increase glucocorticoids from the placenta, which inhibits progesterone.
- Fetal oxytocin is produced
What can be given to induce labour?
How can prostaglandins be given to induce labour?
Oral or into vagina
Give an example of when labour may need to be induced
What are prostaglandins?
Powerful contractors of smooth muscle
What are prostaglandins involved in, regarding the cervix?
What stimulates prostaglandin synthesis in labour?
- Increase in oestrogen:progesterone ratio
- Mechanical damage
What synthesises prostaglandins in pregnancy?
What happens to prostaglandin synthesis in the third trimester?
There is increased synthesis by the amnion
What happens to the levels of prostaglandins in amniotic fluid very early in labour?
What is cervical ripening due to?
Oestrogen, relaxin, and prostaglandins breaking down the connective tissue
What does oxytocin do in labour?
Initiates uterine contractions
What happens to the action of oxytocin during pregnancy?
It is inhibited by progsterone, relaxin, and low number of oxytocin receptors
What happens to the number of gap junctions during pregnancy?
Why does the number of gap junctions increase in pregnancy?
To aid communication between muscle cells, which coordinates uterine activity
What happens to the myometrium at 36 weeks of pregnancy?
There is an increased number of oxytocin receptors in the myometrium
What is the result of the increased number of oxytocin receptors in the myometrium from 36 weeks?
Uterus can respond to pulsatile release of oxytocin from posterior pituitary gland
What special properties does the myometrium have?
Does not act like smooth muscle normally does in that myometrial fibres contract, but only partially relax, and so myometrial muscle does not return to its original size, and there is pernament partial shortening of muscle fibres
What is the result of the pernament partial shortening of the muscle fibres of the myometrium?
Propels fetus furthern into pelvis
What are the features of the contration of the myometrium in labour?
- Symmetry and polarity
What is meant by symmetry and polarity in myometrial contraction?
The contrations create two poles of uterus, then go to fundus and upper part of uterus, then down to the lower segment
What is the result of symmetry and polarity of myometrial contraction?
The forces of the upper segment are more powerful than that of the lower segment of the utersu
What is meant by retraction in the contraction of the myometrium?
After each contraction, the length of the myometrium muscle of the uterus cannot return to the former length, it becomes shorter and shorter.
What is the result of retraction of the myometrium?
The uterine capacity is progressively reduced so the pressure inside the uterus becomes stronger and stronger
How many contractions are required for an effective labour?
3-4 in 10 minutes
What happens to levels of relaxin during pregnancy?
What is the result of increasing levels of relaxin during pregnancy?
Causes changes in the cervix
What changes in the cervix are caused by increasing levels of relaxin?
Causes enzymes to degrade collagen and so changes in collagen to ground substance ratio
Over what time period to the changes in the cervix caused by relaxin occur?
Period of weeks, evident from 36/40
How does a labour cervix allow for delivery?
Offers less resistance to the presenting part
What are the cervical changes during labour known as?
Effacement and dilatation
Describe the cervix in mid-pregnancy?
Unripe - form, not much give, tubular, closed
What happens to the cervix in late pregnancy?
What causes the changes in the cervix from early to late pregnancy?
Oestrogen, prostaglandins, and relaxin increase, causing dispersion of proteoglycan complexes and an increase in collagenase
Describe a term cervix
Softened and effaced
What causes the changes in the cervix between late pregnancy and term?
Uterine contractions before and during labour cause retraction of the myometrium
When is a cervix considered to be fully dilated?
When it can't be felt
What is the ideal pelvis for childbirth?
What are the features of a gynaecoid pelvis?
- Wide forepelvis
- Straight side walls
- Wide suprapubic arch
What pelvices may cause problems in delivery?
Describe the features of an anthropoid pelvis
- Narrow transverse diameter
- Wide AP diameter
- Divergent forepelvis
- Narrow side walls
- Wide inclination of the sacrum
What often happens with an anthropoid pelvis?
Baby doesn't engage
Describe the features of the android pelvis
- Narrow forepelvis
- Convergent side walls
- Forward inclination of the sacrum
- Narrow subpubic arch
Where is the platypelloid pelvis often seen?
In African populations
What often happens with platypelloid pelvis?
Don't get engagement until very late in labour
Describe the features of the platypelloid pelvis
- AP diameter narrow
- Forepelvis straight
- Side walls wide
- Inclination of sacrum narrow
- Subpubic arch wide
What happens in pelvimetry?
Do an x-ray to determine measurements of pelvis
Why isn't pelvimetry done any more?
Not an accurate measurement beacsue cartilage relaxes, so may change
What are the ideal measurements in pelvimetry?
- Transverse diameter of inlet = 13.5cm
- Interspinous diameter = 10cm
- Obstectrical diameter = 10.5cm
What are the potential presentations?
What is the presenting diameter in vertex presentation?
What position is the baby in with vertex presentation?
Chin on chest, smallest diameter coming out through pelvis
What is the presenting diameter in a sinciput presentation?
What is the presentating diameter in brow presentation?
What is the presenting diameter in face presentation?
What is the result of the 9.5cm presenting diameter with face presentation?
Can be delivered vaginally, because same as vertex presentation
What soft tissues constitute the passageway in labour?
When may the cervix cause problems with delivery?
If have had treatment for abnormal smear, can have scarring and stenosis
When may the vagina cause problems with delivery?
What may be necessary when the perineum stops the head from crowning?
May need epistiotomy
What changes to the pelvic floor occur during labour?
- Stretching of fibres of levator ani
- Thinning of central portion of the perineum to almost transparent membranous structure
What 'passenger' factors may cause problems with labour?
What may cause a big fetus?
Why can number of fetuses cause problems with labour?
More fetuses = more likely to be breech
What aspects of fetal position can cause problems in labour?
What is the ideal lie for labour?
What lie may cause problems in labour?
What can happen when a fetus has a transverse lie?
Can cause umbilical cord prolapse
What happens when there is an umbilical cord prolapse?
The cord can go into spasm, stopping oxygen going to the baby
What happens when a mother is found to have a transverse lie?
They are usually admitted at 37 weeks, and if not stabalised by term, C-section
What are the potential attitudes of the fetus?
- Flexion - back of head facing canal
- Extension - face to canal
What are the types of breech presentation?
- Frank breech
- Full breech
- Single footling breech
What position is the fetus in with a Frank breech?
Knees straight, buttocks to canal
What position is the fetus in with a full breech?
What needs to be done with a single footling breech?
Why is a C-section needed with a single-footling breech?
Risk of cord prolapse
What does the first stage of labour constitute?
The interval between the onset of labour and full cervical dilation
What are the phases of the first stage of labour?
- Latent phase
- Active phase
What happens in the latent phase of the first stage of labour?
Onset of labour with slow cervical dilation to 4cm
How long does the latent phase of the first stage of labour take?
Variable duration - can take days
What happens in the active phase of the first stage of labour?
Faster rate of cervical change, 1-1.2 cm/hour and regular uterine contractions
When is someone considered to be in the second stage of labour?
Once they are 10cm dilated
What happens once a person is fully dilated?
Wait an hour to allow contractions to push the baby down, and then push for one hour
Why is a woman only told to push for one hour?
Any longer would be very exhausted
What % of maternal mortality is due to obstructed labour?
What can result from obstructed labour?
- Death of fetus
- Rupture of uterus
What can be done in obstructed labour?
- Operative delivery
What kind of incision is used in a caesarean section?
What is required in addition to incision in a C-section?
Hand pushing to act as contractions
What can be used in an operative delivery?
- Vacuum extraction
When are forceps useful?
When the baby is in the wrong position - can rotate and delivery
When does the 3rd stage of labour commence?
When there is completed birth of the baby
When does the 3rd stage of labour end?
With the complete expulsion of the placenta and membranes
How long does the 3rd stage of labour last?
Usually between 5 and 15 minutes, but any period up to 1 hour may be considered within normal limits
What happens if the placenta is not delivered within an hour?
Take to theatre
Why must a patient be taken to theatre if placenta not delivered within 1 hour?
Risk of infection or heavy bleeding
What happens to the size of the uterus after the baby is born?
There is a marked reduction
Why is there a marked reduction in the size of the uterus after the baby is born?
Due to powerful contraction and retraction (ongoing)
What happens to the placenta as a result in the reduction in size of the uterus after the baby is born?
It is reduced
By how much is the size of the placenta reduced due to the reduction in size of the uterus after the baby is born?
Can be up to 1/2 before seperation begins
What is the effect of uterine contraction on the post-birth placenta?
Inelastic placenta is squeexed, and peels away
What happens to the blood supply to the placenta after birth?
- Blood in intervillous space forced back into veins of spongy layer of decidua basalis.
- Veins become tense and congested, and kept under pressure by underlying muscle of uterus
- Blood can't drain back into the maternal bloodstream because the uterus has retracted and doesn't allow it
What are the signs that the placenta has seperated?
- Fundus retracted
What can happen if the midwife pulls on the cord before the placenta is fully seperated?
Can get prolapse of the uterus
What is the normal blood flow to the placenta site?
500-800ml/minute (10-15% of cardiac output)
What is critical for minimising blood loss in women who have just given birth?
Normal physiological processes
When may there be lots of bleeding after giving birth?
If no uterine contractions
What can be given to a women to get uterus contracting after giving birth to prevent bleeding?
What does syntometrine consist of?
What is the effect of the oxytocin in syntrometrine?
Causes uterine contractions within seconds (short term)
What is the effect of the ergometrine in syntrometrine?
More sustained tonic contraction
What is the advantage of syntrometrine?
Shown to produce significant reduction in maternal death
What physiological processes control bleeding in women who have just given birth?
- Powerful contraction/retraction of uterus, especially action of interlacing muscle fibres which constrict blood vessels running through myometrium
- Pressure exerted on placental site by walls of contracted uterus
- Blood clotting mechanism
When does pressure exerted on placenta walls by sides of the contracted uterus control bleeding?
After placenta and membranes have been delivered