Flashcards in Week 10 - Partuition Deck (45):
-Transition from pregnant state to non-pregnant state at the end of gestation due to expulsion of products after 24 weeks
When is delivery classsed as pre-term?
-Befre 36 weeks
When is delivery classed as post-term?
-After 42 weeks
When does the uterus become palpable in pregnancy?
When does the uterus reach umbilicus during pregnancy?
When does the uterus reach the xiphisternum during pregnancy?
Why would a nurse weight the placenta after delivery?
-Often weighs the same as the baby so measures it to ensure all the placenta has been delivered
Why does the fundus move back towards the pubic symphysis at term?
-Fetal head has moved into pelvic inlet
What 3 positional factors need to be assessed towards the end of pregnancy?
-Lie -> Relationship of the long axis of the baby to the uterus
-Presentation -> Which part of the fetus is adjacent to the pelvic inlet
-Vertex -> Relationship of fetus along its axis in relation to presenting part
What is the most common positions of lie, presentation and vertex of a baby?
-Lie -> Normally longitudinal and fetus flexed
-Presentation -> Normally the head
-Vertex -> minimal diameter between presenting part and pelvic inlet
Give some abnormal presentations of the fetus at the end of pregnancy
-Breech (buttocks or foot)
In normal presentation, what is the average diameter of the head?
What is the average size of the pelvic inlet?
What can increase the size of the pelvic inlet?
-Softening of the ligaments by MMP2 and MMP9
Briefly, what is the first stage of labour?
-Creation of the birth canal by expansion of the soft tissues (Cervix, uterus and vagina) and cervical ripening
What is cervical ripening?
-Process in the first stage of labour where the thick tough cervical collagen is softened
-Involves reduction in collagen through enzymatic degradation, increases in GAGs in order to separate strands and reduce aggregation, increase in hyaluronic acid to draw in water so tissues expand
What triggers cervical ripening?
-Prostaglandins (E2 and F2x)
What effect do contractions have in the first stage of labour?
-Thin the cervix (effacement) and then dilate it
What happens to the myometrium during pregnancy?
-Thickens due to increased cell size and glycogen deposition
What generates the force in uterine smooth muscle cells?
-Intracellular apparatus of actin and myosin triggered by an increase in intracellular calcium due to action potentials arriving at the cell membrane
What allows the smooth muscle to all contract unanimously?
-Specialised gap junctions allows the action potential to spread from cell to cell allowing coordinated contractions of the myometrium
What are pacemaker cells of the fundus? How is this beneficial?
-Cells which can spontaneously depolarise and generate action potentials
-Allows the myometrium to always be spontaneously motile
Describe the contractions in early pregnancy
-Approximately every 30 mins or so but are of low amplitude so cannot be felt
Describe how the amplitude and frequency of contractions changes throughout pregnancy
-Frequency falls throughout pregnancy with an increase in amplitude
-Can produce noticable 'Braxton-Hicks' contractions mid gestation
-Onset of labour characterised by a sudden increase in apmplitude and frequency of contractions
Which two hormones are indicated in the sudden onset of increased amplitude and frequency of contractions?
What is the major producer of prostaglandins throughout preganancy?
What controls the release of prostaglandins from the endometrium?
(low ratio = low synthesis, high ratio=high synthesis)
During labour, what is suspected to causes an increase in prostaglandin synthesis and thus increased contractions?
-Fall in prgesterone
How does oxytocin exert its effects on the endometrium?
-Binds to receptors on smooth muscle cells
What increases the endometrial sensitivity to oxytocin?
-Increase in oestrogen:progesterone ratio
What is the furgeson reflex? What is its purpose?
-As contractions increase, sensory receptors in the cervix and vagina are stimulated. The excitation passes via afferent nerves to the hypothalmus which ultimately promotes oxytocin release
-This enters a positive feedback cycle as increased oxytocin increases the frequency and force of contractions which further stimulates oxytocin release and so on
What is oxytocin?
-A peptide hormone secreted from the posterior pituitary which lowers the threshold for action potentials to generate contraction of smooth muscle cells making contractions more frequent and forceful
What is brachystasis?
-Muscle fibres contract more than they relax so gets progressively shorter, particuarly in the fundal region, therefore pushes the presenting part into the pelvic inlet and cervix
Why does fetal oxygen reduce during labour?
-Forceful uterine contractions temporarily interrupt placental blood supply thus reducing o2 supply to fetus -> needs to be monitored to make sure not excessive
What marks the end of the first stage of labour?
-Dilation of the cervix to 10cm
Which stage of labour is the quickest?
Describe the second stage of labour
-Head flexes as it meets the pelvic floor
-Crowning as head is delivered it rotates and extends back to original position
-Shoulders rotate, followed by the head and the shoulders deliver followed by the rest of the body
What marks the end of the second stage of labour?
-Delivery of the fetus
Describe the 3rd stage of labour
-After the fetus is removed there is a powerful contraction which separates the placenta from the uterus
-Placenta and membranes expelled withing 10 minures
Besides from delivery of the placenta, why is the powerful contraction of the third stage of labour crucial?
-Compress the blood vessels to reduced the bleeding of the uterus
Whaat tirggers the fetus to take its first breatg?
-Environmental stimuli eg light, temperature change, noise, trauma
Describe the vascular changes which occur in the fetus after delivery
-First breath causes a dramatic fall in pulmoonary resistance which reduced pulmonary arterial pressure -> reduced pressure in RA lower than LA -> closure of foramen ovale
-Rising arterial pO2 causes coontraction of smooth muscle in DA
-As the umbilical cord is clamped, removal of placental supply causes the sphincter in DV constricts and DV closes
What is the Apgar score?
-A system used to monitor the fetus after birt
How can post-partuition haemmorhage be limited medically?