Problems with Labour Flashcards
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?
- Powers
- Passenger
- Passage
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?
Increases excitability
Where is oxytocin secreted from?
Maternal posteiror pituitary gland
What effect does mechanically stretching uterine smooth muscle in labour have?
Increases contractility
What does cervical stretching elicit in labour?
Uterine contractions
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?
Prostaglandins
How can prostaglandins be given to induce labour?
Oral or into vagina
Give an example of when labour may need to be induced
In pre-eclampsia
What are prostaglandins?
Powerful contractors of smooth muscle
What are prostaglandins involved in, regarding the cervix?
Cervical softening
What stimulates prostaglandin synthesis in labour?
- Increase in oestrogen:progesterone ratio
- Mechanical damage
What synthesises prostaglandins in pregnancy?
- Placenta
- Decidua
- Myometrium
- Membranes
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?
They rise
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?
It increases
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
- Retraction
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?
Levels increase
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?
It softens
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