Labour and Delivery

Question 1

What are the stages of labour?

Answer 1

First stage = creation of birth canal

Second stage = descent, rotation, delivery

Third stage = placental delivery

Question 2

Outline the first stage of labour

Answer 2

Contractions begin

Descent of fetal head into birth canal

Creation of birth canal

1) latent phase = slow cervical softening, shortening, opening
2) active phase = faster rate of change, regular contractions

Question 3

Outline the second stage of labour

Answer 3

Fetal head descent and rotation through the dilated cervix, birth canal and delivery

1) passive phase = descent and rotation
2) active phase = maternal effort to expel the fetus and achieve birth

Question 4

Outline the third stage of labour

Answer 4

Delivery of placenta

Usually 5-15 mins

Question 5

How does labour get initiated?

Answer 5

Rise in oestrogen:progesterone ratio

Prostaglandins = initiate softening of cervix, maintain/initiate uterine contractions

Oxytocin = uterine contractions

Question 6

Outline the functions of prostaglandins

Answer 6

Induce cervical ripening

Induce cervical contractions

Increase myometrial sensitivity to oxytocin

Raise intracellular Ca = myometrial cell contract

Enhance myometrial gap junctions = strengthen contractions

Question 7

What is cervical ripening?

Answer 7

The changes in the cervix when labour is being initiated

1) reduction in collagen
2) increases in GAGs
3) increase in hyaluronic acid
4) reduced aggregation of collagen fibres

Due to oestrogen, relaxin and prostaglandins breaking down the connective tissue

Question 8

Where are prostaglandins produced?

Answer 8

Mainly in myometrium and decidua

Increased synthesis by amnion in third trimester

Released from cervical stretching

Question 9

How does progesterone effect contractions?

Answer 9

Inhibits

Relative fall in progesterone = facilitates myometral excitability

Question 10

Where is oxytocin secreted from and how is it controlled?

Answer 10

Secreted by posterior pituitary

Controlled by hypothalamus = +ve feedback from cervix and vagina (Ferguson reflex)

Question 11

What is the role of oxytocin?

Answer 11

Initiates uterine contractions

Increases prod of prostaglandins which increase the contractions further

Question 12

What increases the number of oxytocin receptors?

Answer 12

Oestrogen

Question 13

Define cervical effacement

Answer 13

Thinning of the cervix = cervical ripening

Question 14

What is the normal diameter of the birth canal?

Answer 14

9.5/10cm

Max size determined by the pelvis but softening of ligs may increase it

Question 15

Describe the contraction of myometrium during labour

Answer 15

Contracts but only partially relaxes = doesn’t return to original size

Contraction from 2 poles – then fundus – then lower segment

Forces in upper segment more powerful than lower segment

Question 16

How is labour induced?

Answer 16

Stimulate release of prostaglandins – membrane rupture

Artificial prostaglandins

Synthetic oxytocin

Anti-progesterone agents

Question 17

How can the physiology be monitored during labour?

Answer 17

Maternal

• HR, P, T
• contractions
• cervical dilation

Fetal

• colour and amount of amniotic fluid
• scalp capillary pH, acid/base balance

Partogram - fetal HR, cervical dilation (1cm/h), station, contractions, maternal obs

Question 18

Outline the mechanism of labour

Answer 18

Head flexes = present minimum diameter

Head rotates internally = hits levator ani which contracts and rotates it (head tucked under and facing backwards)

Head crowns = stretches perineal muscle and skin

Extension of head and external rotation

Shoulder rotate, shoulders delivery – followed rapidly by body

Question 19

How can delivery be facilitated?

Answer 19

Cesarean section

Forceps

Vacuum extraction

Question 20

Describe the separation and descent of the placenta

Answer 20

Baby born = reduced uterus size

Inelastic placenta squeezed by contraction

Question 21

How is bleeding controlled?

Answer 21

Powerful contractions of uterus = constrict blood vessels through myometrium

Pressure on placental site by wall of contracted uterus

Blood clotting

Question 22

Describe the control of milk let down

Answer 22

Suckling = activation of mechanoreceptors = up spinal cord to hypothalamus = 1) on signal to PP to prod oxytocin, 2) off signal to AP to stop prod dopamine, which allows prolactin to be secreted

Prolactin = milk fat synthesis

Oxytocin = stim myoepithelial cell = milk ejection

Question 23

Order the cardinal movement of labour

Answer 23

engage
flexion of the neck
rotation
extension of the neck
restitution
delivery of anterior shoulder
delivery of posterior shouder

Question 24

What does the first stage of labour end with?

Answer 24

Ripening = pull dilation of the cervix

Question 25

What is the most common cause of post-partum haemorrhage?

Answer 25

uterine atony = uterus fails to contract after delivery

Question 26

What hormonal change is responsible for secretion of milk after delivery?

Answer 26

decreased progesterone and oestrogen

Question 27

Outline ‘failure to progress’

Answer 27

Delay in 1st or 2nd stage

Causes = inadequate contractions, malposition/malpresentation, cephalopelvic disproportion, obstructed labour, maternal exhaustion

Inadequate contractions = oxytocin

Question 28

What are the causes of fetal compromise and how should it be managed?

Answer 28

Causes:

• uterine hyperstimulation (?iatrogenic)
• hypotension
• poor tolerance of labour
• cord compression
• infection
• maternal disease

Mx

• rectify reversible causes
• L lateral position
• stop oxytocics
• confirm comprise by FBS
• deliver by speediest route

Question 29

Discuss operative delivery

Answer 29

Ventouse, forceps

Indications = failure to progress in 2nd stage, fetal distress in 2nd stage, maternal reasons

Requirements = fully dilated, absent membranes, cephalic presentation, empty bladder

Comp = failure, maternal/fetal trauma, postpartum haemorrhage, urinary retention, cephalhaematoma (forceps)

Question 30

What is the Bishop score?

Answer 30

Assessment of cervical ripeness which predicts whether induction of labour will be required

Score <4 – labour is unlikely to progress naturally

Factors = cervical feature, dilation, length, station, consistency, position

Question 31

Briefly outline abnormal fetal HR patterns and the causes

Answer 31

Tachy (>160) = Fetal hypoxia, Chorioamnionitis – if maternal fever also present, Hyperthyroidism, Fetal or maternal anaemia, Fetal tachyarrhythmia

Brady (<100) = Prolonged cord compression, Cord prolapse, Epidural and spinal anaesthesia, Maternal seizures, Rapid fetal descent

Normal variability is between 5-25 bpm

Reduced variability =

• Fetal sleeping: should last no longer than 40 minutes (most common cause)
• Fetal acidosis (due to hypoxia) – more likely if late decelerations are also present
• Fetal tachycardia
• Drugs – opiates / benzodiazepines / methyldopa / magnesium sulphate
• Prematurity – variability is reduced at earlier gestation (<28 weeks)
• Congenital heart abnormalities

Early deceleration = normal
Late deceleration = insufficient blood flow to the uterus and placenta (hypotension, pre-eclampsia, uterine hyperstimulation)