2b. Labour Flashcards
Define miscarriage
Loss of a non-viable pregnancy
Usually occurs within 13 weeks of fertilisation
What would be the time frame considered as term?
37-41 weeks of gestation
What would be the time frame considered as preterm?
23-37 weeks of gestation
Often occurs due to preterm labour as we cannot easily stop labour once it has been induced
What would be the size of a baby born in term?
Length of the body of the baby is the size of a human forearm and the head is the size of a human hand
How are the baby’s structures different in preterm delivery?
All the structures are present but they are much smaller and may not work properly
What does it mean to be in labour?
- Fundally dominated contractions - The uterus is undergoing regular coordinated contractions - they go from the top of the uterus (fundus) and pushes downwards so the baby moves towards the cervix
- Cervical ripening and effacement - the cervix is a thick structure that holds the baby in place. It must relax to let the baby out during labour which involves tissue change along it the contractions
Outline the different processes that occur in labour
Cervical ripening and effacement (increasing)
Co-ordinated myometrial contractions (increasing)
Rupture of fetal membranes
Delivery of infant
Delivery of placenta
Contraction of uterus
What are braxton hicks contractions? What is the function of these?
When the uterus contacts partly or when it contracts then relaxes again
The uterus is relaxed throughout pregnancy to allow growth of the fetus so these small contractions are a training phase which allows the uterus to get into the routine of contracting
How long does labour last for?
12-48 hours
What happens in each of the three phases of labour?
Phase 1 - the contractions and cervical changes start (longest part of pregnancy as the uterus has to go from relaxed to contracting)
Phase 2 - delivery of the baby
Phase 3 - delivery of the placenta
What initiates human term labour and pre-term labour?
Term - could be low progesterone, oestrogen CRH or oxytocin but not sure Pre-term - Intrauterine infection Intrauterine bleeding Multiple pregnancy Stress (maternal)
What happens in cervical ripening and effacement? What molecules are involved?
Change from rigid to flexible structure Remodelling (loss) of extracellular matrix Recruitment of leukocytes (neutrophils) Inflammatory process -Prostaglandin E2, interleukin-8 -Local (paracrine) change in IL-8
What happens in myometrial contractions? What are the key mediators involved?
Fundal dominance Increased co-ordination of contractions Increased power of contractions Key mediators -Prostaglandin F2a (E2) levels increased from fetal membranes -Oxytocin receptor increased -Contraction associated proteins
What happens in the rupture of fetal membranes during labour?
Loss of strength due to changes in amnion basement component
Inflammatory changes, leukocyte recruitment
-Modest in normal labour, exacerbated in preterm labour
Increased levels and activity of MMPs
Inflammatory process in fetal membranes
What is the main transcription factor involved in these inflammatory processes?
NF-kB
What does NF-kB do?
Upregulates inflammatory molecules such as:
COX-2 (prostaglandins - PGs), IL-8, IL-1b, MMPs, Oxytocin receptor, PG receptors; contraction-associated proteins
Why is it hard to stop labour once it has been initiated?
There are many different initiators of labour that increase NF-kB levels so it will be hard to turn them all off
Molecules formed due to NF-kB such as IL-1b can further increase NF-kB levels resulting in a feed forward loop
What is one of the main causes of preterm labour?
Activators of inflammation (e.g. intrauterine infection)
What are the two main molecules involved in term labour?
CRH and PAF (platelet activating factor)
CRH levels steeply rise in the 3 weeks before delivery
What is the function of platelet activating factor and where is it found?
Part of lung surfactant which is needed to allow the baby to breathe
Surfactant proteins and complexes
Produced by maturing lung, before birth
Levels in amniotic fluid increase near term
Fetal signal of maturity - matured lungs produce a factor which allows the baby to then be born
What do CRH and PAF produce?
Prostaglandins from fetal membranes
What is the function of the increasing levels of CHR?
CRH is normally produced in the placenta, and the levels are low in early pregnancy. As pregnancy proceeds, levels of CRH produced increase. It goes through the umbilical cord to the baby, and works on the baby’s HPA axis (stimulates ACTH production, which in turn stimulates the foetal adrenal glands).
The adrenal gland, under stimulation, produces cortisol which causes lung maturation (and also travels back, via the umbilical cord, to the placenta).
Cortisol normally switches DOWN the production of CRH (negative feedback). In the placenta, cortisol switches UP CRH production (feed-forward loop). More CRH and more cortisol feedback loop. There is a rapid rise in CRH in the last few weeks of pregnancy
How does CRH upegulate PAF and how does this then act?
The high levels of CRH will start to switch UP IL and prostaglandin production in the foetal membranes
Cortisol from the adrenal gland is acting on the foetal lung
It stimulates the foetal lungs to produce surfactant (including PAF)
Lungs are in intimate contact with amniotic fluid (baby takes amniotic fluid into lungs, and expels it)
This allows PAF to enter the amniotic fluid, and PAF upregulates the same factors in the membranes
PAF is a signal that the lungs are mature, and therefore the baby is safe to be born
What is the function of DHEAS
This is a steroid produced in the adrenal glands
It can move to the placenta and can be converted to oestrogens (it is an oesrogen precursor)
Oestrogens upregulate PGs, OT and OT receptors – all required for increased myometrial contractility
What hormone is absolutely necessary for preganancy to occur and what happens to this during labour?
Progesterone
Its effects are lost in normal term labour
How does progesterone stop labour from occurring?
During pregnancy, there are a lot of progesterone receptors as well as progesterone present
The receptors can bind to NF-kB and stop it from activating pro-inflammatory molecules
Why do the effects of progesterone cease at the end of pregnancy and how is labour then induced?
Progesterone receptor levels decrease at the end of pregnancy. This means that progesterone can’t have its effect and NF-kB will also be unbound and can exert its pro-inflammatory effects
What is this process of reduced progesterone function called?
Functional progesterone withdrawal - Progesterone itself is not removed but its function is reduced
What are the different progesterone receptors and how do the proportion of these change?
PR-B mediates the main effects of progesterone via gene expression
PR-A is less able to mediate these effects
Ratio of PR-A : PR-B increases at term
Loss or change in PR may lead to ‘functional progesterone withdrawal’
