Learning outcome
1. Describe the initiation and maintenance of labour and delivery
2. Describe the change in the cervix and uterus at the onset of labour
3. Describe the three stages of labour
4. Define pre-term labour
LO 1 : Describe the initiation and maintenance of labour and delivery
Causes of onset of labour
- Uterine distension
- Feto placenta contribution
- Oestrogen
- Progesterone
- Prostaglandins
- Oxytocin
- Neurological factor
Hormonal changes :
- Ostrogen increase
- Prostaglandin increase
- Oxytocin increase
- Progesterone decrease
-
Oestrogen increase
to increase the excitability of myometrium membrane and increase the synthesis of prostaglandin
It stimulates the release of oxytocin from maternal pituitary by promoting the synthesis of oxytocin
receptor in the myometrium and decidua.
It stimulates the synthesis of myometrial contractile protein and increase excitability of the
myometrial cell membrane
Increase in prostaglandin
- which initiate and maintain labour . this is the main hormone that start labour.
- If there is no contraction at week 42, they induce labour using prostaglandin
- The major site of synthesis of prostaglandins are amnion, chorion, decidual cells and myometrium
- Synthesis of prostaglandin is triggered by the rise in glucocorticoids, mechanical stretching in the
late pregnancy , increase in cytokines, infection, vaginal examination, separation or rupture of
membrane
- Fetal membrane produce PGE2 that act as direct vasodilator by acting on smooth muscle to cause
dilatation of the blood vessel, promote cervical ripening
Cervical ripening - the process of softening and widening the cervix in preparation of childbirth
Increase oxytocin
- Oxytocin is synthesis from maternal and fetal pituitary.
- Oxytocin increases as oxytocin receptors are increased in the uterus with the onset of labour
- Oxytocin will promote the release of prostaglandin from the decidua and fetal membrane
Decidua cell – the specialized layer of endometrium that forms the base of the placental bed
-
Vaginal exam and amniotomy cause the rise in maternal plasma oxytocin level
( ferguson reflex ( fetal ejaction reflex) is the neuroendocrine reflex comprising the self- sustaining
cycle of uterine contractions initiated by the pressure at the cervix or vaginal wall) this is an
example of positive feedback ( as it leads to increase in oxytocin to increase contraction of the
uterus)
Ferguson reflex occur as fetus stimulate the nerve receptor in the pelvic floor, cervix and upper
portion of vagina which then result in the urge to push
-
Increase in oxytocin maintain the uterine contractibility
Decrease progesterone
- to reduce the uterine relaxation. ( Offer progesterone if pregnant mother has history of preterm
labour to support growth of fetus in the uterus
- plasma progesterone remain constant but the number of progesterone receptor in the cervix and
myometrium are decreasing.
- It is the alteration in the oestrogen progesterone ratio rather than the absolute fall in the absolute
concentration of progesterone shich is linked with the prostaglandin synthesis
LO 2 : Describe the change in the cervix and uterus at the onset of labour