Session 10: Labour and Delivery Flashcards
What is labour?
When pregnancy end with the expulsion of the products of conception (fetus + placenta).
This is specifically after 24 weeks of gestation.
If pregnancy ends before 24 weeks, what is it called?
Spontaneous abortion (miscarriage)
What is labour called that happens before the 37th week of gestation?
Pre-term labour
Expulsion of the fetus requires a few processes. Which?
Creation of birth canal
Release of the structures that normally retain the fetus in utero.
Enlargement and realignment of the cervix and vagina.
Expulsion of the fetus.
Expulsion of the placenta and changes to minimise the blood loss of the mother.
What happens in the first stage of labour?
Creation of birth canal
Release of the structures that normally retain the fetus in utero
Enlargement and realignment of the cervix and vagina.
What does the lie of the fetus mean?
The relationship of the long axis of the fetus to the long axis of the uterus.
What is the commonest lie?
Longitudinal with the head or buttocks posterior.
What is the presentation of the fetus?
Which part of the fetus that is adjacent to the pelvic inlet.
In case of a longitudinal lie, what may be the presentation of the fetus?
Head (cephalic) or breech (podalic)
State lie and presentation in each picture.
What is the most common presentation and lie?
What is the diameter of the presentation in this case?
Longitudinal and cephalic so that the vertex presents.
9.5 cm
What is the pelvic inlet boundaries?
Pos - sacral promontory
Anteriorly - superior pubic rami and the upper margin of the pubic symphysis
Laterally - ilio-pectinal line
What is the true diameter of the pelvic inlet?
11 cm
Give mechanisms that occur some expansion of the pelvic inlet.
Softening of pelvic ligaments
What is the fetus normally retained in the uterus by?
Relative inactivity of the myometrium
The cervix
What does the cervix need to do in order to create a birth canal?
Dilate and retract anteriorly.
What is cervical dilation due to?
Structural changes known as cervical ripening.
Forceful contractions of uterine smooth muscle.
The contractions first thin the cervix and then dilate it.
Explain cervical ripening.
Marked reduction in collagen and marked increase in GAGs.
Collagen bundles loosen.
Influx of inflammatory cells and increase in NO output.
What is the cervical ripening triggered by?
Prostaglandins like E2 and F2alpha
Explain what happens to the myometrium during pregnancy.
It gets thicker (10x in hypertrophy) and also due to glycogen depositions.
How can the myometrium be described in the pattern of contractions?
Always spontaenously motile as the smooth muscle cells contract in coordination and are capable of spontaneously depolarise.
Pattern of contractions of myometrium in early pregnancy.
Around every 30 minutes but low amplitude so might not be noticeable.
What happens as pregnancy progresses?
The contractions decrease in frequency but increase in amplitude.
What are these noticeable contractions called?
Braxton-Hicks contraction
What happens to the contraction at the onset of labour?
There is a sudden increase in frequency as well as amplitude (force)
What hormones facilitates the change in manners of the contractions?
Prostaglandins
Oxytocin
Explain prostaglandins role in myometrial contractions.
Enhance the release of calcium from intracellular stores
Explain oxytocin’s role in myometrial contractions.
Lower the threshold for triggering APs (increases frequency)
Explain the Ferguson Reflex.
As contractions increase in frequency and amplitude the secretion of oxytocin will increase massively.
This is by sensory receptors in cervix and vagina.
This is an example of positive feedback as oxytocin will make the contractions even more forceful and frequent.
What is brachystasis?
Each contraction of the myometrium casuses the muscle fibres to shorten, however they will not relax fully.
This will lead to the uterus and in particular the fundus to shorten progressively.
This pushes the presenting part into birth canal and stretches the cervix over it.
What can be given medically to induce labour?
Prostaglandin
How might the fetus become distressed during labour?
Increasingly forceful uterine contractions may temporarily reduce placental blood flow. This leads to a reduced oxygen supply to the fetus.
When does the first stage of labour end?
Cervical dilation reaches 10 cm
How long does the second stage usually last?
1 hour (multiparous)
2 hrs (primigravida)
Explain the sequence of the second stage of labour.
Descended head of the fetus flexes when it meets the pelvic floor. This reduces the diameter of presentation.
Internal rotation ensues
The flexed head descends to the vulva to stretch the vagina and perineum.
Head is delivered and as it emerges it will rotate back and extend.
Shoulders rotate followed by the head. As the shoulders deliver, the rest of the fetus will follow quickly.
What does the second stage of labour end with?
Delivery of the fetus
When does the third stage of labour start?
When the fetus is delivered
Sequence of the third stage of labour.
Powerful uterine contractions which causes the placenta to separate as well as position it into upper part of the vagina, or lower uterine segment.
The placenta and membranes are then expelled.
How quickly after stage 2 is the placenta usually delivered?
Within 10 minutes
What other benefits does the contraction of the uterus have?
Compression of blood vessels and reduce bleeding.
What can the contraction of the uterus be enhanced by?
Administration of oxytocic drugs.
Explain cardiovascular changes post-partum of the fetus.
Foramen ovale shuts due to change in atrial pressure
Ductus arteriosus constricts due to an increase in arterial pO2.
Sphincter in the ductus venosus constricts
Give examples of fetal circulatory shunts.
Patent foramen ovale (Atrial septal defect)
Patent ductus arteriosus
Patent ductus venosus
How can the well-being of the neonate be assessed following delivery?
APGAR score
When is the APGAR score used?
Soon after delivery and then 5 minutes later.
Explain the APGAR score.
Appearance
Pulse
Grimace
Activity
Respiration
How can the elements of labour be classified?
The Powers
The Passage
The Passenger
Explain the powers.
Contraction of myometrium (hypertrophy + hyperplasia)
Shortening of fundus
Uterine contractions such as frequency, amplitude and duration
Give examples of failure of labour might happen.
Inadequate power (insufficient uterine contractions)
Inadequate passage (abnormal pelvis, rigid perineum)
Abnormalities of passenger (macrosomia, fetal presentation)
How is progress in labour plotted graphically?
Partogram
