13 Physiology and mechanics of labour

Question 1

what are the two stages of labour?

Answer 1

1. dilating cervix
2. push baby out through birth canal

Question 2

mechanism of cervical dilatation

Answer 2

upper segment (smooth muscle) contracts

lower segment (collagen) passively dilates

Question 3

effacement of cervix

Answer 3

Length of cervix becomes smaller until becomes just a hole

Question 4

how is the progress in labour monitored graphically?

Answer 4

partogram

Question 5

problems during labour

Answer 5

• reduced utero-placental blood flow during contraction
• baby develops hypoxaemia, acidosis- may die
• normal babies have glycogen stores in liver and can survive
• if labour longer than normal and placenta not working well- baby starts with less glycogen so can become hypoxic

Question 6

baby mortality

Answer 6

final trimester: approx 1-2 per 1000

day of labour 10-50 per 1000

no monitoring/ treatment 5% die modern obstetrics 1/2000

Question 7

fetal monitoring in labour

Answer 7

• fetal hr
• uterine contractions

Question 8

what to do when there is fetal distress?

Answer 8

C-section

controversial: many C sections to prevent one death
- fetal hr monitor isnt very specific, lots of babies have abnormal heart rate

Question 9

what do with slow progress?

Answer 9

• amniotomy: rupture membrane
• oxytocin: causes more contractions

both can harm baby

Question 10

Answer 10

biggest part of baby

joins at soft spot- anterior frontanelle

Question 11

position of baby’s head

Answer 11

left occipito-lateral

Question 12

Answer 12

occipito- anterior

Question 13

Answer 13

occipito posterior

Question 14

which plane is the maternal pelvis inlet widest?

which plane is the maternal pelvis outlet widest?

what plane is the baby’s skull widest?

what does this mean for baby’s head?

Answer 14

transverse

AP

AP

head must rotate

Question 15

Mechanism of labour

Answer 15

1. flexion
2. descend in transverse position
3. internal rotation (shoulder enter inlet)
4. delivery by extension
5. external rotation/ restitution
6. anterior shoulder
7. posterior shoulder
8. body delivers like a fish

Question 16

most common delivery position of baby?

Answer 16

left occipitut- anterior

Question 17

mal-positions/ presentations

Answer 17

• Occipito-posterior position
• Occipito-lateral position (stuck in lateral position)
• Brow presentation- partial extension, failure to flex, dimensions of head too big. C section
• Face presentation- excess extension, c section
• Breech presentation- turned around wrong way, bum first. Can deliver but tricky, danger head caught
• Shoulder presentation- c section