What is term delivery?
37-41 weeks gestational age (since LMP)
What is birth?
The final phase of pregnancy
What is pre-term delivery?
22-37 weeks gestational age (since LMP)
What is very pre-term delivery?
28-32 weeks gestational age (since LMP)
What are the key tissues involved in labour?
Cervix
Myometrium
Foetal membranes
Summarise the main biochemical processes of labour (endocrine, inflamm)
Foetal membranes:
- Inflammatory process
- PGs, ILs, MMPs
- Waters breaking
Cervix: dilation (effacement, ripening)
- IL-8, PGE2, MMPs
Myometrium:
- Increased contraction associated proteins
- Increased oxytocin receptors
- PGF2a (E2) levels increased from foetal membranes
How is the cervix assessed before the onset of labour?
Bishop’s score
- Pre-labour scoring system to assist in predicting whether induction of labour will be required
- Also used to assess likelihood of spontaneous preterm delivery
Total score calculated by assessing 5 components on manual vaginal examination:
- Cervical dilation in cm
- Cervical effacement as %
- Cervical consistency
- Cervical position
- Foetal station - position of foetal head in relation to pelvic bones
Call PEDS For Parturition! = Cervical Position, Effacement, Dilation, Softness; Foetal Station
What occurs during cervical ripening?
- Cervix becomes softer + more flexible
- Change from rigid to flexible structure
- Remodelling (loss) of ECM
- Recruitment of leukocytes (neutrophils)
- Inflammatory process - PGE2, IL-8
- Paracrine (local) change in IL-8
What are the 3 stages of labour?
- Cervical dilation - effacement + ripening
- Expulsion of infant
- Afterbirth - delivery of placenta
What happens in the first stage of labour?
- Cervix is undilated - too narrow
- High conc of oxytocin being released from neurohypophysis causing uterine contractions
- Contractions cause membranes surrounding foetus to release PGs that soften up cervix + cause more uterine contractions
- Positive feedback loop between uterine contractions + PG release = true labour
- Sides of uterus contract upwards, which pulls cervix thinner and causes it to open up
- Contractions push foetus against cervix –> dilates even more
- Relaxin released from placenta dilates cervix
- Mucus plug (seals opening of cervix during pregnancy) comes out and discharged out of vagina
- Can happen up to 2 days before to during labour
- Amniotic sac ruptures (foetal membranes)
- When cervix dilates to 4cm –> body moves into active labour –> stronger + closer together contractions
- Max diameter - 10cm –> urge to push –> 2nd stage of labour
What triggers relaxin release from the placenta?
- Progesterone starts to drop off at 37 weeks
- Higher oestrone:progesterone ration caused increased uterine contractions (false labour)
- Placenta releases relaxin
What does relaxin do?
- Relaxes pelvic ligaments so pelvic bones can part to support enlarging uterus
- Opens up pelvic outlet by loosening pubic symphysis
- Helps dilate cervix during labour
What happens in the 2nd stage of labour?
Expulsion on infant
- Starts when foetal head enters birth canal
- Uterus continues to rhythmically contract to push baby out
- Skull bones of newborn aren’t fully fused - slide over top of each other and compress each other enough to get skull thr birth canal
What happens in the 3rdd stage of labour?
- Afterbirth
- Delivery of placenta + associated membranes
- Uterus continues to contract after abby delivered
- Causes placenta to detach from walls of uterus and eject out of vagina
- Uterus continues to contract to help uterus to return to pre-gestation size = involution
- Allows abdominal organs to return to original positions
What happens in the 3rdd stage of labour?
- Afterbirth
- Delivery of placenta + associated membranes
- Uterus continues to contract after abby delivered
- Causes placenta to detach from walls of uterus and eject out of vagina
- Uterus continues to contract to help uterus to return to pre-gestation size = involution
- Allows abdominal organs to return to original positions
What occurs during cervical dilatation?
- Cervix becomes thinner + wider
What happens during the rupture of foetal membranes?
- Loss of strength due to changes to amnion basement component
- Inflamm changes, leukocyte recruitment
- Increased levels and activity of MMPs
- Inflamm process in foetal membranes
What is cervical effacement?
Thinning of cervix
