10. Birth

Question 1

What happens in the first stage of labour?

Answer 1

Creation of the birth canal, onset of labour to full cervical dilation.

Question 2

What are the phases in the first stage of labour?

Answer 2

Latent and active phases.

Question 3

Describe the latent phase of the first stage of labour.

Answer 3

Onset to 4cm dilation, slow.

Question 4

Describe the active phase of the first stage of labour.

Answer 4

Faster rate of cervical change, 1-1.2cm/hour. Regular uterine contractions.

Question 5

What happens in the second stage of labour?

Answer 5

Expulsion of foetus.

Question 6

Describe the second stage of labour.

Answer 6

Rapid (takes up to an hour), urge to bear down.

Question 7

Describe the movements of the foetus in the second stage of labour.

Answer 7

Descended head flexes as it reaches the pelvic floor - reduces presentation diameter. Internal rotation. Head stretches vagina and perineum. Head deliver - rotates and extends. Shoulders rotate and deliver. Rest of body follows rapidly.

Question 8

What is the risk in the second stage of labour and how is it avoided?

Answer 8

Risk of tearing perineum, avoided by episiotomy.

Question 9

What happens in the third stage of labour?

Answer 9

Expulsion of placenta, sheared off by strong contractions of uterus.

Question 10

Describe the third stage of labour.

Answer 10

Contraction of uterus shears off placenta, compresses blood vessels to reduce haemorrhage. 5-15 minutes.

Question 11

Which soft tissues are expanded in creation of a birth canal?

Answer 11

Cervix, vagina, perineum.

Question 12

What does the birth canal expand to and generally how?

Answer 12

To 10cm, structural changes + lots of force.

Question 13

What is the maximum size of birth canal determined by?

Answer 13

The pelvic, softening of ligaments may increase it.

Question 14

What is the cervix made of in pregnancy?

Answer 14

Tough, thick collagen, coiled for structural strength.

Question 15

What is cervical ripening?

Answer 15

Softening of the cervix for birth.

Question 16

What does cervical ripening involve?

Answer 16

Reduced collagen production, increased glycosaminoglycans (disrupt matrix), reduced aggregation of collagen fibres (uncoils).

Question 17

What triggers cervical ripening?

Answer 17

Prostaglandins E2 and F2x, locally diffused from uterus.

Question 18

How does myometrium change through pregnancy for cervical ripening?

Answer 18

Smooth muscle increases in pregnancy. Force generate with raised [Ca2+]i from spontaneous action potentials.

Question 19

How is premature labour prevented?

Answer 19

Progesterone suppresses myometrial contractions until the proper time.

Question 20

How do uterine contraction differ in early and late pregnancy?

Answer 20

Early - low amplitude, every 20 minutes, mother unaware.

Late - higher amplitude, less frequent, ‘Braxton-Hicks’ contractions.

Question 21

How are uterine contractions made more forceful and frequent?

Answer 21

Prostaglandins + ripening of cervix - increase [Ca2+]i per action potential.
Oxytocin -> more action potentials with lower threshold.

Question 22

What are prostaglandins?

Answer 22

Biologically active lipids, local hormones.

Question 23

Where are prostaglandins produced?

Answer 23

Mainly in endometrium.

Question 24

What controls production of prostaglandins throughout pregnancy?

Answer 24

Oestrogen:progesteroner ratio.
P>O -> low prostaglandins throughout pregnancy.
O>P -> increased prostaglandins at end of pregnancy.

Question 25

Where is oxytocin secreted from?

Answer 25

Posterior pituitary under control of hypothalamus.

Question 26

How is oxytocin secretion increased?

Answer 26

By afferent impulses from cervix and vagina in Ferguson reflex - mechanical stimulation of cervix from prostaglandin contraction so more oxytocin secretion, strengthened contractions, cervix stimulated more so more oxytocin etc.

Question 27

What is the role of oxytocin?

Answer 27

Acts on smooth muscle receptors, acts on more if O>P.

Question 28

What is brachystasis?

Answer 28

Uterine smooth muscle relaxes less than it contracts. A feature of uterine smooth muscle that drives the presenting part of the foetus to the cervix.

Question 29

Describe the normal physiological processes which initiate labour.

Answer 29

Increased foetal cortisol -> O>P -> increased prostaglandins from endometrium of uterus -> increased force of contractions. Then a loop: cervix stretched -> oxytocin release from posterior pituitary in Ferguson reflex -> increased uterine contractions -> cervix stretched etc.

Question 30

What are the immediate physiological changes in the neonate which enable independent life?

Answer 30

Takes first breath so foetal circulation -> adult circulation. Reduced pulmonary vascular resistance so blood fills lungs and increased return to LA => pressure LA > RA so foramen ovale closes. Increased arterial pO2 -> ductus arteriosus contracts.

Question 31

What is the Apgar score?

Answer 31

Assesses condition of neonate scoring 0-10 according to colour, tone, pulse, respiration, response.

Question 32

What is the risk of haemorrhage in birth?

Answer 32

Uterus contracts after neonate has been born to shear off and expel placenta which leaves maternal blood vessels exposed -> risk of haemorrhage as blood to this site is 500-800ml/minute.

Question 33

How is maternal blood loss limited after birth?

Answer 33

Uterine contraction continues to compress placental blood vessels through myometrium to close them off. Enhanced effect with oxytocic drug.

Question 34

What is the common foetal presentation?

Answer 34

Baby lies longitudinally, in cephalic presentation, well flexed so vertex presents to pelvic inlet. Diameter of presentation is 9.5cm.

Question 35

What are the elements of labour?

Answer 35

The powers, the passage, the passenger.

Question 36

What are the powers of labour?

Answer 36

Deliver of foetus depends on contraction of myometrium that has undergone hypertrophy and hyperplasia in pregnancy. Contraction and retraction of smooth muscle fibres shortens the fundus of uterus.

Question 37

What is the passage of labour?

Answer 37

Bony pelvis and soft tissues. Pelvic inlet - shorter in AP plane, 10.5cm diameter. Pelvic cavity - circular, 12cm diameter. Pelvic outlet - shorter in ML plane, 11cm diameter.

Question 38

What is the passenger of labour?

Answer 38

Size and presentation of foetus - orientation of head of foetus when entering pelvis is important.

Question 39

What may failure to progress in labour be due to?

Answer 39

Inadequate power - insufficient uterine contraction. Inadequate passage - abnormal bony pelvis, rigid perineum. Abnormalities of passenger - foetus too big, foetal/breech presentation.

Question 40

How can labour be induced?

Answer 40

Give the mother prostaglandins + oxytocic drugs -> cervix ripens and uterus begins contractions.

Question 41

What does a foetal scalp electrode assess in labour?

Answer 41

Foetal heart rate.

Question 42

How is caesarean section delivery performed?

Answer 42

Suprapubic incision. Linea alba and anterior layers of rectus sheaths are transected and resected superiorly. Rectus muscles are retracted laterally or divided through tendinous parts allowing reattachment without muscle fibres injury.

Question 43

What tools in operative delivery assist in delivery?

Answer 43

Forceps, vacuum extraction.