Mechanism of labour

Question 1

What is labour?

Answer 1

Labour consists of the combination of painful uterine Contractions + Dilatation of the Cervix to expel the foetus + placenta from the uterus

Question 2

What are the stages of labour?

Answer 2

Stage one: Full dilation of the cervix up to 10 cm. lasts up to 8 hours in nulliparous women.

Stage two: full dilation till expulsion of the foetus

Stage three: delivery of foetus - expulsion of placenta

Question 3

What are the mechanical factors of labour?

Answer 3

1. Power: 40-50 second contractions every 2-4 mis. Lead to dilation of cervix with pressure from the head. Weak contractions in nulliparous women + IOL.
2. Passenger: three main considerations.
   a. Pelvic inlet: transverse part > AP
   b. Mid cavity: Transverse = AP
   c. Pelvic outlet: AP > transverse.
   Ischial spine is used to assess decent. station 0: head is at the level of IS.
3. Passenger: diameter of head, presentation, presenting part + attitude of head.

Question 4

What is the first step in labour?

Answer 4

Engagement - where the head enters the pelvis in the occipital-transverse position

Question 5

What is the second step in labour?

Answer 5

Descent and flexion - where the head decent into the mid-cavity. Head station calculated.

Question 6

What is the third step in labour?

Answer 6

Internal rotation - where the head rotates int he mid-cavity to become facing the AP side.

Question 7

What is the fourth step in labour?

Answer 7

Head delivery by extension - then rotates 90 degrees (same position as when it entered the inlet to endure shoulders are delivered.

Question 8

What is attitude in labour?

Answer 8

flexion + Extension of the foetal head on neck to make the foetal presentation larger/smaller

Question 9

What is foetal head moulding?

Answer 9

Compression of the head due to suture overlapping to reduce head diameter

Question 10

What is Foetal head caput?

Answer 10

localised scalp swelling due to pressure of cervix/pelvis on scalp.

Question 11

How is the placenta delivered?

Answer 11

physiological - maternal effort

active - Controlled cord traction to prevent uterine inversion

Question 12

What foetal landmarks are felt on vaginal exam?

Answer 12

1. Anterior frontanelle
2. posterior frontanelle
3. occipital bone - used to describe diameter

Question 13

What is the most common cause of death during labour in the UK?

Answer 13

1. Sepsis
2. DVT
3. PPH

Question 14

How do you examine a lady in labour?

Answer 14

1. Feel stomach for 10 mins to assess contractions
2. abdominal examination: to feel for position and engagement
3. vaginal examination: feel head to check position and assess cervical dilation

Question 15

What are signs of placental separation?

Answer 15

1. lengthening cord
2. rising + firming of the fund’s of the uterus
3. Seperation vagina l bleed

Question 16

Define a prolonged third stage of labour

Answer 16

Physiological - more than 1 hour

With management - 30 mins

Question 17

What is physiological expulsion of the placenta:

Answer 17

1. delivery of the placenta by maternal effort
2. No uterotonic drugs used
3. No clamping of the umbilical cord until pulsation has stopped

Question 18

What is active management of stage 3?

Answer 18

1. controlled traction of the cord after signs of placental seperation
2. use of uterotonic drugs

Question 19

What are the 2 uterotonic drugs used?

Answer 19

1. oxytocin
2. Syntometrin: contracts the uterus to expel placenta + Stop bleeding. + closes blood vessels causing severe Hypertension.

Question 20

What landmark is used to calculate the station?

Answer 20

Ischial spine