Normal Pregnancy: Physiology of Labour Flashcards
incl dating and diagnosing pregnancy and factors affecting accurate dating
What is labour?
the onset of regular and painful contractions associated with cervical dilation and descent of the presenting part
When do labour and delivery normally occur?
between 37 and 42 weeks gestation
What are the 3 stages of labour?
First stage
– from the onset of labour (true contractions) until 10cm cervical dilatation (fully dilated) creates the birth canal
Second stage
– from 10cm cervical dilatation until delivery of the baby
Third stage
– from delivery of the baby until delivery of the placenta
Describe the first stage of labour in more detail:
1. What are the 3 phases of the FIRST stage of labour
Latent phase
– 0 - 3cm dilation of cervix
- 0.5cm p/hour
- IRREGULAR contractions
Active phase
–3cm - 7cm dilation of cervix
- 1cm p/hour
- REGULAR contractions
Transition phase
–7cm - 10cm dilation of cervix
-1cm p/hour
- STRONG + REGULAR contractions)
Describing the first stage of labour in more detail:
2. What needs to happen to the cervix?
- Cervical dilation (opening up) and effacement (getting thinner)
- “Show” which refers to mucus plug in the cervix which stops bacteria entering the uterus during pregnancy. It falls out and makes space for baby to pass through
What are some signs of labour ?
- Regular and painful uterine contractions
- A “show” (shedding of mucous plug from cervix)
- Rupture of the membranes (not always)
- Shortening and dilation of the cervix
What do Nice guidelines intraprtum care (2017) state are the definitions (Zero to finals)
1. Latent first stage
2. Established first stage of labour
- Latent first stage
- Painful contractions
- Changes to the cervix, with effacement and dilation up to 4cm - Established first stage of labour
- Regular, painful contractions
- Dilatation of the cervix from 4cm onwards
Outline the methods of monitoring a woman and her baby during labour
- FHR monitored every 15min (or continuously via CTG)
- Contractions assessed every 30min
- Maternal pulse rate assessed every 60min
- Maternal BP and temp should be checked every 4 hours
- Vaginal Exam should be offered every 4 hours to check progression of labour
*Maternal urine should be checked for ketones and protein every 4 hours
What are Braxton- Hicks?
-occasional irregular contractions of the uterine smooth muscle (from 2nd + 3rd trimester)
- Character: temporary, irregular tightening or mild cramping in the abdomen.
- Not true contractions, do not indicate the onset of labour. They do not progress or become regular.
Staying hydrated and relaxing can help reduce Braxton-Hicks contractions.
Physiology: (Teach me physiology)
For labour to commence, ‘cervical ripening’ needs to occur and the uterine myometrium needs to become more excitable.
Explain the concept and process of ‘cervical ripening’
Concept : Softening of cervix (allowing it to dilate) and offer less resistance to foetus
Process:
Oestrogen, relaxin and prostaglandins (especially important) break down cervical CT. Synthesis increases in 3rd trimester in the oestrogen: progesterone ratio
Ripening involves:
A reduction in collagen.
An increase in glycosaminoglycans.
An increase in hyaluronic acid.
Reduced aggregation of collagen fibres.
Physiology: (Teach me physiology)
For labour to commence, ‘cervical ripening’ needs to occur and the uterine myometrium needs to become more excitable.
Explain the concept of myometrial excitability
- Relative decrease in progesterone (in relation to oestrogen) occurs in the 3rd trimester
- This increases the excitability of uterine musculature because progesterone inhibits contractions while oestrogen increases the gap junctions between SM cells - increasing contractility)
- Mechanical stretching of uterus as baby grows also works to increase contractility
Physiology: (Teach me physiology)
For labour to commence, ‘cervical ripening’ needs to occur and the uterine myometrium needs to become more excitable.
Explain the concept of myometrial excitability
- Relative decrease in progesterone (in relation to oestrogen) occurs in the 3rd trimester
- This increases the excitability of uterine musculature because progesterone inhibits contractions while oestrogen increases the gap junctions between SM cells - increasing contractility)
- Mechanical stretching of uterus as baby grows also works to increase contractility
Outline the role Oxytocin in initiating uterine contractions
- In pregnancy oxytocin is inhibited by relaxin and progesterone + has low number of oxytocin receptors
- At 36 weeks influence of oestrogen increases the number of oxytocin receptors in the myometrium
- uterus responds to pulsatile release of oxytocin from posterior pituitary gland
- Positive feedback loop begins as afferent impulses from the cervix and vagina cause increase in oxytocin production.
- Post pituitary releases more oxytocin -> stronger contractions -> drives the process of labour = “Ferguson reflex”
What is the size of the birth canal?
The maximum size of the birth canal is determined by the pelvis – the pelvic inlet is typically around 11cm
-May increase slightly during pregnancy as ligaments soften under the influence of hormones.
What is the size of the birth canal?
The maximum size of the birth canal is determined by the pelvis – the pelvic inlet is typically around 11cm
-May increase slightly during pregnancy as ligaments soften under the influence of hormones.
At the end of the first stage of labour, where will the foetal head be and in what position?
Once the cervix is dilated (10cm) the foetal head is able to descend, remaining flexed to maintain the smallest diameter possible.
Describe the movements made by baby following path of least resistance through the birth canal during delivery
How to calculate the expexted date of delivery (EDD) or the Naegele rule?
1.Determine the first day of the last menstrual period.
- Next, count back 3 calendar months from that date.
- Lastly, add 1 year and 7 days to that date.
