Labour and Delivery

Question 1

Define the stages of labour

Answer 1

• First stage - creation of the birth canal and dilation of cervix
  
  • Latent phase - onset of labour with slow cervical dilation but softening
  • Active phase - faster rate of change and regular contractions
• Second stage - changes in uterine contractions to allow descent of fetus through the birth canal and delivery
  
  • Fetus undergoes descent and rotation of the head
• Third stage - expulsion of the placenta and contraction of uterus

Question 2

What initiates labour

Answer 2

• Rupture of fetal membranes - water breaking
• Labour triggered by rise in oestrogen to progesterone ratio
  
  • Increases prostaglandin
    
    • Increases myometrial sensitivity to oxytocin

Question 3

Describe the synthesis and action of prostaglandins during labour

Answer 3

• Powerful contractors of smooth muscle and involved in cervical softening
  
  • Release oxytocin release to further maintain uterine contractions
• Synthesis stimulated by increase in oestrogen to progesterone ratio and mechanical damage
• Synthesized in placenta, decidua, myometrium and membranes

Question 4

Describe the action of oxytocin in labour

Answer 4

• Initiates uterine smooth muscle contractions
• Action inhibited in pregnancy by progesterone, relaxin and low oxytocin receptors
• At 36 weeks, increased number of oxytocin receptors in myometrium
• Secreted by posterior pituitary

Question 5

Describe the function of cervical ripening

Answer 5

• Cervical ripening = softening of cervix = effacement
• During pregnancy, cervix is rigid and closed
• During labour, cervix softened and dilated to prepare for baby
• Cervix dilate up to 10cm during labour

Question 6

Decsribe the mechanism of cervical ripening

Answer 6

• Cervical ripening due to oestrogen, relaxin and prostaglandins breaking down connective tissue
• Cervix collagen in proteoglycan matrix
  
  • Ripening involves reduction in collaged, increase in glycosaminoglycans and increases in hyaluronic acid
  • Reduced aggregation of collagen fibres
    
    • Increased water content between fibres

Question 7

Describe the processes in creating a birth canal

Answer 7

• Maximum size of birth canal determined by pelvis
  
  • Pelvic inlet typically 11cm
• Softening of ligaments increases size of birth canal - increased gap between pubic symphysis
  
  • Stimulated by progesterone and oestrogen
• Stretching of the fibres of the levator ani and the thinning of the central portion of perineum transforms to almost transparent membranous structure

Question 8

How is birth canal assessed

Answer 8

• Assessment of birth canal done through ultrasound scan
  
  • Assess if size of fetus is able to pass through birth canal
  • Assess size of fetus head
    
    • Assess position of the fetus

Question 9

Describe the properties of myometrium

Answer 9

• Most muscles normally contract and relax
• Myometrial fibres contract but only partially relax
  
  • Does not return to its original size
• Permanent partial shortening of the muscle fibres

Question 10

Describe the contraction and retraction concept of the uterus and how it helps labour

Answer 10

• After each contraction, the uterus cannot return to the former length, becoming shorter and shorter
• Uterine capacity is progressively reduced so the pressure inside uterus becomes stronger and stronger
• By increasing the pressure within the uterus, it can help push the baby through the uterus
• Retraction process also reduces blood loss through post-partum haemorrhage

Question 11

Describe in outline the most common fetal presentations

Answer 11

• Lie - longitudinal or transverse
• Attitude - flexion or extension
• Presentation - frank breach, full breach, single footing breach

Question 12

Describe how labour can be induced

Answer 12

• Stimulate release of prostaglandins - membrane rupture
• Artificial prostaglandins
• Synthetic oxytocin
• Anti-progesterone agents

Question 13

What factors of the fetus are monitored during labour

Answer 13

• Heart rate patterns
• Maternal temperature
• Colour and amount of amniotic fluid
• Scalp capillary pH

Question 14

Describe the mechanism of the second stage of labour

Answer 14

• Head of fetus flexes first (into transverse position - sideways)
  
  • Minimum diameter through pubic symphysis
• Head then rotates internally to become backward facing
• ‘Crowning’ - head stretches perineal muscle and skin
• Extension of head and restitution (external rotation) as the baby comes out
• Shoulders rotate followed by body (anterior shoulder delivery)

Question 15

Explain Erb’s palsy and relate it to labour

Answer 15

• Damage to upper brachial plexus
• Occurs when a baby’s neck is stretched too far or when shoulders cannot pass through birth canal
• Arm down, wrist flexed, forearm pronated
• Inhibition or paralysis to raised arm

Question 16

Describe, in principle, how delivery may be facilitated by intervention

Answer 16

• Cesarean section - incision through skin and uterus to remove baby
• Operative delivery - forceps or vacuum extraction
• Pain relief such as epidural given
  
  • Inserted into L1-L4 and blocks T9-S4

Question 17

Describe the processes which normally limit maternal blood loss after birth

Answer 17

• Uterus size decreases through contraction and retraction process
  
  • Reduces the size of placental site - forces placenta out
  • Pressure exerted on placental site by walls of contracted uterus
• Living ligature - interlacing muscle fibres of uterus constrict blood vessels running through the myometrium
• Blood clotting mechanism

Question 18

Define post-partum haemorrhage and state its most common cause

Answer 18

• Post-partum haemorrhage - loss of >500mL of blood after vaginal delivery
• Most commonly caused by uterine atony - failure for uterus to contract after giving birth

Question 19

Describe the hormonal control of the growth and development of mammary tissues

Answer 19

• Progesterone, oestrogen, prolactin, growth hormone and adrenal steroids cause hypertrophy in pre-existing alveolar-lobular structures in the breast
• Formation of new alveolae occurs by budding from the milk ducts
• During puberty when oestrogen is secreted, it increases fat stores in the breast and produces the duct system
  - Secretory glands grow when menstruation begins

Question 20

What stimulates milk production immediately after birth

Answer 20

• Decrease in oestrogen and progesterone levels

- Have inhibitory effect on prolactin

Question 21

Describe the hormonal control of milk production

Answer 21

• Prolactin is released by the action of suckling, which becomes increasingly sensitive to prolactin release
• Dopamine (prolactin inhibiting hormone) release is inhibited from hypothalamus

Question 22

Outline how milk is stored within the breast

Answer 22

• Milk is produced and stored in the mammary alveoli within the breast
• Milk secretion also dependent on adequate emptying of the secreting glands
  
  • Accumulation of milk inside alveoli causes distension and atrophy of glandular epithelium
    
    • Need constant feeding to maintain adequate milk secretion

Question 23

Describe the control of milk let down

Answer 23

• Oxytocin causes contraction of the myoepithelial cells around the alveolae
  
  • Causes alveolae to contract and expel the milk into the milk-collecting ducts
  • Longitudinal muscle cells along the collecting ducts also stimulated to dilate them and improve flow to nipple
• ‘Let down’ reflex - oxytocin is released in response to suckling, seeing or hearing a baby
  
  • Readily inhibited by emotional stress or anxiety
    
    • Oxytocin released in pulsatile manner from posterior pituitary

Question 24

Describe the physiological process of labour initiation

Answer 24

1. Fetal distress stimulates ACTH release from the fetus
2. Causes cortisol production in the adrenal glands of the fetus
3. Cortisol effects the placenta by decreases progesterone and oestrogen but increasing prostaglandin levels in the mother, which act to allow uterine contractions
4. Uterine and cervix stretch, which stimulate stretch receptors
5. Sensory stretch fibres stimulate oxytocin release from the hypothalamus
6. Oxytocin is stored in the posterior pituitary and released
7. Oxytocin causes further uterine contractions and stimulates uterus to produce more prostaglandins
8. This then further stretches the uterus and cervix, causing more oxytocin and prostaglandin release through positive feedback