S8.1 Labour & Delivery Flashcards
Define parturition
Transition from pregnant to non-pregnant state
Define labour
Physiologic process by which a fetus is expelled from the uterus
Define delivery
The method of expulsion of the fetus, transforming fetus to neonate
Briefly describe stage 1 of labour - creation of the birth canal
Baby settles lower into pelvis, in response cervix effaces (becomes thinner) and dilates.
By the end the cervix dilates to 10cm
Describe stage 2 of labour - expulsion of the foetus
Once the cervix is fully dilated, head moved into birth canal.
Head flexes and rotates internally.
Active segment of uterus contracts and pushes baby downwards, passive segment relaxes to allow baby to pass through.
When head is delivered, it rotates and extends the shoulders rotate and body is delivered
Describe stage 3 of labour - expulsion of placenta
Uterus contracts hard to expel placenta.
Normally occurs within 10 min of foetus expulsion.
Once placenta expelled, uterus contracts and reduces in size
Describe the common foetal positions
Lie - relationship of foetal long axis to the long axis of the uterus, normally longitudinal (upside down), foetus normally flexed.
Attitude – normally flexed (head, arms and legs flexed against mothers trunk).
Presentation – crowning (head first, normal), breech (shoulder or knee first), footling breech.
Describe how a birth canal is created through cervical ripening
Triggered by prostaglandins PGE2 and PGF2alpha.
Involves a reduction in collagen and aggregation of collagen fibres.
Also an increase in glycosaminoglycans.
This all results in cervical effacement and dilatation.
Oestrogen relaxes the pelvic ligaments
Relaxin breaks down connective tissue
Describe how uterine contractions facilitate labour
In early pregnancy, there are little twitches at low amplitude every 30 minutes.
Middle pregnancy less frequent.
Late pregnancy around 35w get ‘Braxton-Hicks’ contractions which are low frequency but higher amplitude.
How do prostaglandins control contractility?
Prostaglandins makes forceful contractions
Controlled by oestrogen:progesterone ratio.
Progesterone inhibits contraction
Oestrogen increases contractility by increasing gap junction communication
How does oxytocin control contractility?
Creates more action potentials by lowering threshold.
Stimulates uterus to contract and stimulates placenta to secrete prostaglandins.
What is the Ferguson reflex?
Increase in oxytocin release from posterior pituitary, by afferent impulses from cervix and vagina.
Causes more forceful contractions
Describe the structure of the myometrium during pregnancy?
During pregnancy is thicker due to hypertrophy and glycogen deposition
Summarise the physiological processes which initiate labour
More prostaglandins: cervix ripens, uterus contracts more strongly, brachystasis
Cervix dilates and effaces
Ferguson reflex as contractions increase, stimulates oxytocin release - contracts more forcefully and frequently
Describe the processes which limit maternal blood loss after birth
Uterine contractions compress spiral arteries.
Blood clotting mechanisms
