8: Parturition Flashcards
Describe the relationship between cervical effacement and cervical dilation
Effacement is thinning/flattening of the cervix
(ideally you want a 100% effaced cervix)
A softer (cervical ripening) and thinner cervix -> easier to dilate
Prostaglandin synthesis increases in response to what?
Relative fall in progesterone in comparison to estrogen
*either via progesterone drop or estrogen increase
When does the first stage of labour end?
When the cervix is fully dilated at 10 cm
Reasons for failure to progress can be divided into separate categories. List the categories and give an example of each
- Power - inadequate contractions
- Passage - abnormally shaped pelvis
- Passenger - large-sized fetus, number and position
What is labour progression plotted on?
Partogram
How does the diameter of the pelvic inlet change during pregnancy?
Softening of ligaments surrounding pelvic inlet -> increases diameter
What is considered an ideal orientation for the fetus to be in delivery and why?
Longitudinal lie, cephalic presentation with the head flexed so that the vertex is the presenting part.
What could you ask about the contractions to determine whether an individual is in labour?
The intensity and frequency of contractions
What is special about the way uterine muscles contract in labour compared to normal muscle contractions?
Brachystasis; myometrial fibres partially relax and cannot return to their original size -> permanent shortening of muscle fibres with each contraction -> increases pressure in uterus -> drives fetus out birth canal
What features of the cervix would you assess to determine whether the patient is in active labour?
Dilation, effacement and how short it’s become
Describe the mechanism by which the force of contractions is increased during labour?
Ferguson reflex.
Contractions detected by sensory receptors in cervix and vagina -> afferent to hypothalamus -> increased oxytocin release -> acts on uterus
a)Increase FOC
b)increased circulating prostaglandins -> increases frequency
-> contractions lead to more pressure -> positive feedback until pressure is released when the baby passes
What happens to the mother’s uterus after the fetus has been expelled?
What can be given if it’s not happening as quickly as it should?
Uterus continues to contract and shrink -> squashes and seales arteries in the endometrium -> blood can’t drain into the maternal bloodstream -> prevents maternal hemorrhage and completes the separation.
Can give synthetic oxytocin to increase/facilitate contractions
When is the baby considered to be pre-term?
before 37 weeks
What defines the first stage of labour and what are the two phases?
Interval between the onset of labour and full cervical dilation/creation of the birth canal through expansion of soft tissues
- Latent phase: slow cervical dilation, contractions becoming more regular and intense. Progresses to..
- Active phase: faster rate cervical change and regular uterine contractions
What marks the end of the second and third stages of labour? How long does each of them typically take?
Second: delivery of the fetus, usually up to 1 hr
Third: delivery of placenta + membranes, usually 5-15 min
Which scan helps determine whether the mother is having single or multiple pregnancies?
The dating scan
How is the method of delivery influenced when the baby is in ‘transverse lie’ or has a breech?
Cesarian section or procedure to externally turn the baby ~ 37 weeks
Which bones make up the pelvis?
Sacrum, coccyx and two hipbones (ischium, ileum and pubis)
When can babies with face cephalic presentation be delivered vaginally?
If they are in the mento-anterior position (not mentoposterior)
Briefly describe the ‘classes’ (3) of a podalic presentation
Classed as a breech
- Frank breech: When hips are flexed but knees extended
- Full breech: hips and knees flexed
- Single footing breech: foot presents out of the cervix
Briefly describe the process of ‘cervical ripening’
Prostaglandins E2 and F2x trigger
- A reduction in collagen
- And an increase in glycosaminoglycans -> reduces aggregation of collagen fibres
- >collagen bundles loosen -> cervix softens
Describe the structural changes (2) of the myometrium to expel the fetus
Hypertrophy of sm muscle cells -> thickens myometrium
Increased glycogen in the muscle -> generates force required to expel the fetus
Describe how uterine contractions change throughout pregnancy and in labour, which hormones are involved?
Pregnancy: begin low force -> become less frequent but more intense
In labor:
a) prostaglandins increase intracellular calcium in sm muscle cells -> force
b) oxytocin lowers threshold for APs -> frequency
What is the structure of oxytocin? Where is it secreted from and what controls its secretions?
High estrogen: progesterone ratio->hypothalamus -> posterior pituitary -> oxytocin (peptide hormone)
How does the influence of oxytocin on the myometrium change throughout pregnancy?
Inhibited first due to progesterone and
low levels of oxytocin receptors found in the myometrium.
Progesterone levels fall ~36 weeks (changing the ratio) -> more oxytocin receptors produced in myometrium -> more susceptible to the pulsatile release from the pituitary
Name four maternal reasons for when artificial initiation of labour might be necessary
Maternal: severe preeclampsia, recurrent antepartum hemorrhage, pre-existing disease (i.e diabetes), social
What is the Bishop’s score used for?
Used by midwives and doctors to asses the ‘readiness’ of the cervix. The more effaced and dilated the cervix, the higher the Bishop’s score, the easier the vaginal passage will be
List three things you can give to induce labour and the pros and cons of each if applicable *list 5 complications for the nonhormonal method
- Prostaglandins (gel, tablet or pessary/in the vagina) ripen the cervix. They reduce the risk of cesareans when compared to using oxytocin alone but miscalculating the dose can hyperstimulate the uterus causing distress on the fetus 2. Oxytocin (IV or synthetic) post SROM or amniotomy. It requires constant fetal monitoring and careful dose titration in accordance with the frequency and strength of contractions 3. Amniotomy: releasing fluid from the amniotic sac to induce labour. Complications include; cord prolapse, infection, failure (to induce efficient contractions), bleeding from vasa praevia, amniotic fluid embolism, etc
When and why would you use cardiotocography?
Monitors the uterine contractions (bottom half) and the fetal HR (top half). A CTG can be used if there are concerns about how labour is progressing and to diagnose any problems
Name two specific things that happen during the second stage of labour
Delivery of the fetus-The presenting part appears in the birth canal-Active contractions increase in strength, duration and frequency and the mother may feel the need to push/bear down
What happens to the fetal head as labour progresses into the second stage?
It becomes flexed to reduce the diameter of the presenting part and rotates internally
What are some complications if the fetus passes through too quickly or is very large? How might this be prevented?
Risk of tearing the perineum. May perform an episiotomy (making a cut in the perineum) to prevent this
What is ‘crowning’? What needs to happen so that the baby’s shoulders can be delivered?
When the baby’s head reaches the vulva and remains visible without slipping back in To deliver the shoulders (has the widest diameter) it must pass through the pelvic outlet transversely, so the baby’s head must externally rotate and extend to line the shoulders transversely
Name six analgesics that can be used during labour and briefly describe each
- Paracetamol 2. Entonox: 50/50 Oxygen/NO; inhaled, effective during the peak of contractions 3. Pethidine; opiates, may cause nausea (50% effective in labouring women, takes 15-20 min to work.)4. Pudendal block5. Epidural (small catheter with local anesthetic and opium mix)6. Spinal anesthetic; useful for theatre intervention (like a cesarian)
What is the Apgar scoring system used for? What defines a ‘healthy baby’ score?
- Activity
- Pulse
- grimace (reflex irritability)
- appearance (skin colour)
- Respiration.
Score: >=7, normal healthy baby
What is one criterion for forms of ‘operate delivery’ to be offered and what are two available methods? Are there any other interventions typically offered in conjunction with forms of an operate delivery?
The baby must be in the appropriate position and descended far enough 1. Forceps: Woman pushes and obstetrician does 3 attempts. Usually, woman has a spinal anesthetic in case there ends up being a need for a cesarian2. Vacuum extraction; cup on baby’s head to extract
Briefly describe how a cesarian section works, how many types are there and what differentiates them? Briefly describe when you would perform types 1 and 4
An incision is made in the mother’s abdomen, the head is delivered first while an assistant applies fundal pressure to the top of the uterus. There are four types that depend on the urgency to deliver 1. There is an immediate risk of life (baby or mother) 4. Elective section, arranged at a date/time suited for surgeon and woman prior to her going into labour to prevent any problems during labour (i.e having a large baby, known to have multiple pregnancies, known problems with her pelvis or uterus, or had a cesarian before)
How else does the ferguson reflex assist in giving birth? (Other than positive feedback cycle with contractions)
Helps cervix dilate and ruptures the amnion
List 4 things that can aid the process of giving birth
- Opening pelvis to 55 degrees
- A water environment reduces gravity.
- Increase pressure on the cervix, i.e standing upright
- Calm environment as oxytocin is released with parasympathetically
Name three fetal reasons why artificial initiation of labour might be necessary
Rhesus disease, prolonged pregnancy, intrauterine growth restriction
