Flashcards in 1st Stage of Labour Deck (65):
What is the definition of labour?
The process by which the fetus, placenta and membranes are expelled through the birth canal
When is the onset of labour normally expected?
Between 37 and 42 weeks gestation or 280 (+/- 10) days
What is the definition of the first stage of labour?
From the onset of regular contractions to complete dilation of the cervix
Do colagen levels in the cervix increase or decrease at the onset of labour and what causes the change?
Decrease caused by an increase in collagenase
Do most cervixes ripen before or after the onset of contractions?
What is effacement?
The process by which the cervical canal is drawn up into the lower segment of the uterus and the cylindrical cervix becomes funnel shaped
What is cervical dilation?
The enlargement of the cervical os from a closed point to an opening wide enough to allow the widest diameter of the presenting part to pass through
What document is the progress of the labour noted on?
What happens once the cervix is stimulated?
It promotes oxytocin release which stimulates uterine contractions and therefore prostaglandin are released.
Name the THREE layers of pregnant uterus
-Inner layer is the decidua
-Middle layer is the myometrium
-Outer layer is the perimetrium
How does oestrogen affect the muscle fibres during pregnancy?
Fibres increase in length (hyperplasia) and in size (hypertrophy)
How far apart and how long lasting are early labour contractions?
15-20 minutes apart
Lasts around 30 second
How far apart and how long lasting are established labour contractions?
3-4 times every 10 minutes
Lasts 50-60 seconds
What is intrauterine hydrostatic pressure?
The pressure exerted on the amniotic fluid by the contractions
What is the resting pressure exerted by the myometrium?
5 mmHg (millimetres of mercury)
What is the pressure of the myometrium in pregnancy?
Up to 30 mmHg (millimetres of mercury)
What is the pressure of the myometrium in labour?
60-80 mmHg (millimetres of mercury)
What does polarity mean during contractions?
The upper and lower poles of the uterus act in harmony, with contraction and retraction of the upper pole and dilatation of the lower pole to allow expulsion of the fetus
What is retraction?
The progressive shortening of the uterine muscle fibres.
The muscles contract during a contraction but instead of fully relaxing, they retain some of the shortening.
What leads to the progressive shortening and thickening of the upper uterine segment?
What is a retraction ring?
A physiological ridge which forms between the upper and lower segments of the uterus
What is the operculum?
The mucous plug located in the cervical os, formed in pregnancy
What is the technical definition of a "show"
The discharge of the operculum which may be blood stained owing to the rupturing of some capillaries when the lining of the cervix is stretched or where the chorion has become detached from the dilating cervix
What are forewaters?
A small sac of amniotic fluid, trapped between the head and the cervix following increased uterine pressure
What are hindwaters?
The amniotic fluid that is not trapped between the head and the cervix
What is meant by general fluid pressure?
The distribution of equal pressure from the contractions, throughout the amniotic fluid
What is fetal axis pressure?
When the membranes have ruptured and amniotic fluid is reduced, the force of the fundal contraction is transmitted to the upper pole of the fetus, down the long axis of the fetal spine, causing increasing flexion of the head. This ensures that the smallest possible circumference (the vertex) is applied to the cervical os
Describe the latent phase of the first stage of labour
The initial part which lasts until cervical dilatation is about 3-4cm which can take 6-8 hours in a primigravida
Describe the active phase in the first stage of labour
From 3-4cm until full dilatation. Rapid rate of dilatation
1cm/hour in primigravida and 1.5cm/hour in multigarvida
What is a cervicograph
The letting of cervical dilatation (in centimetres) against time (in hours)
How can a midwife assess progress during the first stage of labour?
Fetal heart rate
Urinalysis to assess ketone levels
What can be checked during an abdominal examination, to assess the progress during the first stage of labour?
-Assess descent of the fetal head using pelvic palpation
-Assess length and frequency of contractions using lateral palpation
-Assess fetal heart rate using auscultation
What FIVE things can be checked during a vaginal examination, to assess the progress during the first stage of labour?
-Look for the purple line which extends from the anus and up the natal cleft (top of cleft is usually 10cm)
-Confirm head is engaged
-Check if membranes have ruptured
-Assess dilatation and effacement of the cervix
-Assess position of the fetal head in relation to the ischial spines
In the urine, levels of what can be found to increase during labour?
What is a partogram?
A graphical record of the changes that occur during labour, plotted against time, such as:
Fetal heart rate
What is baseline variability?
Looking at a CTG, it is the slight variance of the fetal heart rate (should vary by at least 5 beats over a period of 1 minute)
What is an early deceleration?
A deceleration of the fetal heart rate which occurs at the beginning or just after the onset of the contraction
What is a late deceleration?
A deceleration in the fetal heart rate which begins during or after a contraction, reaches it's lowest point after the peak of the contraction and has not recovered by the time the contraction ends
What is baseline bradycardia?
A fetal heart rate consistently less than 110bpm
What is baseline tachycardia?
A fetal heart rate consistently greater than 160bpm
What is a prolonged deceleration?
When the fetal heart rate drops by 30bpm or more and lasts over 3 min.
How does stretching of the myometrium play a part in the initiation of labour?
It increases uterine muscle excitability
How does ACTH play a part in the initiation of labour?
The fetal adrenal gland becomes more sensitive to ACTH which stimulates the production of cortisol. This then promotes lung maturation and triggers changes in the uterus
How does placental CRH play a part in the initiation of labour?
It stimulates the fetal adrenal gland which increases the amount of DHEAS. This then helps stimulate the production of higher levels of oestrogen. If oestrogen levels are higher than progesterone levels, contractions are triggered
How does oestrogen play a part in the initiation of labour?
Increasing oestrogen levels promote the formation of oxytocin receptors, the majority of which are in the upper uterine segment
What does progesterone do to the uterus during pregnancy?
It maintains the myometrium in a quiescent state
What effect does progesterone have on prostaglandins during pregnancy?
Inhibits the ripening effect they have on the cervix
At how many weeks gestation do oestrogen levels begin to rise?
Around 34 weeks gestation
What effect does oestrogen have on gap junction formation?
It promotes gap junction formation in the myometrium which allows rapid transmission of electrical impulses and chemical signals between the muscle cells
What effect does oestrogen have on oxytocin receptors?
It increases the number of oxytocin receptors in the uterus
Where is the hormone, relaxin, produced?
The corpus luteum
When are levels of relaxin at their highest?
During the 1st trimester
What effect does relaxin have on smooth muscle and the uterus?
It relaxes smooth muscle and suppresses uterine activity
Name the THREE primary prostaglandins
Where is PGF2alpha synthesised and what does it do?
It is synthesised in the placenta, decidua and membranes.
Stimulates the myometrium and contributes to the softening of the cervix
Where is PGE2 synthesised and what does it do?
Synthesised in the placenta, decidua and membranes.
Stimulates the myometrium (10% more than PGF2alpha). Has the most influence on the softening of the cervix
Where is PG12 synthesised and what does it do?
Synthesised predominantly in the myometrium
Relaxes smooth muscle and aids blood flow to the placenta. Contributes to softening of the cervix
Where is oxytocin synthesised and stored?
Synthesised in the hypothalmus and stored in the posterior pituitary gland where it is released in pulses
Where are oxytocin receptors found?
In the decidua, placenta and membranes
What can stimulate the release of oxytocin?
Tactile stimulation of the uterus, vagina and especially the uterus
What effect does oxytocin have on prostaglandins?
Stimulates the release of prostaglandins PGF2alpha and PGE2
Name the THREE muscle layers of the myometrium
Inner circular layer
Middle oblique or spiral layer
Outer longitudinal layer
Where is the inner circular muscle layer of the myometrium found?
Mainly in the cornua and around the cervix
Where is the middle oblique or spiral muscle layer of the myometrium found?
In the upper body of the uterus where the placenta is normally found