10.1 Flashcards
Describe the first stage of labour
Creation of birth canal
Onset of labour leads to full cervical dilation.
Latent phase = onset –> 4cm dilation (slow)
Active phase = faster rate 1-1.2cm/hour, regular uterine contractions.
Describe the second stage of labour
Expulsion of fetus
Relatively rapid Up to one hour but can be fast Urge to bear down and push. Descended head flexes, Internal rotation of head. Stretches vagina and perineum (risk of tearing, allow to tear - along the weakest plane) Head delivered - rotates and extends. Shoulders rotate and deliver. Rapidly followed by rest of body.
Describe the third stage of labour
Expulsion of placenta
Sheared off by strong contractions of the uterus
Contraction of uterus compresses blood vessels to reduce haemorrhage.
Lasts between 5 and 15 mins.
What soft tissues need to expand to create the birth canal?
Cervix
Vagina
Perineum
What is water breaking
At some point in dilation of the cervix, the fetal membranes rupture, releasing amniotic fluid.
To what size does the birth canal expand?
Cervix to around 10 cm
Required both structural changes and force.
In normal presentation, what is the biggest part of the fetus? How big?
Head - 9.5 cm
What determines the maximum size of the birth canal and how big is it? How may this increase?
Pelvic inlet
11cm.
Softening of ligaments, via action of collagenases, may increase this.
What is the cervix made of?
Tough, thick collagen in proteoglycan matrix, which is coiled to give structural strength.
What is cervical ripening
Softening of the cervix:
Enzymatic degradation of collagen
Reduction in collagen production
Increase in glycosaminoglycan - disrupts the matrix
Increased hyaluronic acid
Reduced aggregation of collagen fibres - uncoiling.
What triggers cervical ripening?
Prostaglandin E2 and Prostaglandin F2alpha
(PE2 and PF2alpha)
These locally diffuse from the uterus.
Cause small contractions of the myometrium.
Once released, the cervix is ready to be stretched.
What kind of muscle is myometrium? Describe contraction of the myometrium. How is it triggered.
Smooth muscle.
Triggered spontaneously due to pacemakers in the body of the uterus.
The force generated is when intracellular calcium rises due to action potentials.
These create sustained contractions.
What prevents labour occurring prematurely?
Progesterone
Describe early uterine contractions in pregnancy.
Low amplitude, every 30 minutes
Mother may not be aware
Describe uterine contraction in middle pregnancy.
Higher amplitude, less frequent.
Braxton-Hicks contractions.
Practice for labour
How are the contractions of the uterus made more powerful and frequent?
Prostaglandins
- Increase intracellular calcium per action potential
- Stronger
Oxytocin
- More action potentials
- Lower threshold
What are prostaglandins, where are they produced and how is production controlled?
Biologically active lipids.
Paracrine activity
Produced mainly in endometrium.
Production controlled by Oestrogen:Progesterone ratio.
P > O
- Low prostaglandins
- Throughout pregnancy
(remember P suppresses uterine contraction)
O > P
- Increased prostaglandins
- End of pregnancy
Where is oxytocin secreted from?
Posterior pituitary, controlled by hypothalamus.
What is the Ferguson Reflex?
Mechanical stimulation and pressure to the internal end of the cervix due to prostaglandin contractions increase oxytocin secretion.
These in run stimulate and strengthen contraction, stimulating the cervix more, releasing more oxytocin….
Until baby is delivered.
What does oxytocin act on?
Smooth muscle receptors.
More receptors present if O > P.
What is brachystasis?
Uterine smooth muscle relaxes less than it contracts.
This shortens the fibres in the body of the uterus over time and drives the fetus into the cervix.
What happens to fetal cortisol, oestrogen, progesterone, prostaglandins, uterus, cervix and oxytocin at the end of pregnancy? What is the result?
Fetal cortisol Increased
Oestrogen > Progesterone
Increased prostglandins = stronger contractions.
Uterus contracts - fibres in body shorten.
Cervix is stretched.
Oxytocin increases continually by the Ferguson reflex.
Increased frequency of uterine contraction.
Cervix stretched more.
Labour initiated.
What causes the fetus to take its first breath. What causes this?
Many stimuli, trauma, cold, light, noise
Reduced pulmonary vascular resistance due to increased arterial pO2
What is the Apgar score?
Condition of the neonate assessment.
Assesses:
Colour, tone, pulse, respiration, response
