10.1

Question 1

Describe the first stage of labour

Answer 1

Creation of birth canal

Onset of labour leads to full cervical dilation.
Latent phase = onset –> 4cm dilation (slow)
Active phase = faster rate 1-1.2cm/hour, regular uterine contractions.

Question 2

Describe the second stage of labour

Answer 2

Expulsion of fetus

Relatively rapid
Up to one hour but can be fast
Urge to bear down and push.
Descended head flexes,
Internal rotation of head.
Stretches vagina and perineum (risk of tearing, allow to tear - along the weakest plane)
Head delivered - rotates and extends.
Shoulders rotate and deliver.
Rapidly followed by rest of body.

Question 3

Describe the third stage of labour

Answer 3

Expulsion of placenta

Sheared off by strong contractions of the uterus
Contraction of uterus compresses blood vessels to reduce haemorrhage.
Lasts between 5 and 15 mins.

Question 4

What soft tissues need to expand to create the birth canal?

Answer 4

Cervix
Vagina
Perineum

Question 5

What is water breaking

Answer 5

At some point in dilation of the cervix, the fetal membranes rupture, releasing amniotic fluid.

Question 6

To what size does the birth canal expand?

Answer 6

Cervix to around 10 cm

Required both structural changes and force.

Question 7

In normal presentation, what is the biggest part of the fetus? How big?

Answer 7

Head - 9.5 cm

Question 8

What determines the maximum size of the birth canal and how big is it? How may this increase?

Answer 8

Pelvic inlet
11cm.
Softening of ligaments, via action of collagenases, may increase this.

Question 9

What is the cervix made of?

Answer 9

Tough, thick collagen in proteoglycan matrix, which is coiled to give structural strength.

Question 10

What is cervical ripening

Answer 10

Softening of the cervix:
Enzymatic degradation of collagen
Reduction in collagen production
Increase in glycosaminoglycan - disrupts the matrix
Increased hyaluronic acid
Reduced aggregation of collagen fibres - uncoiling.

Question 11

What triggers cervical ripening?

Answer 11

Prostaglandin E2 and Prostaglandin F2alpha
(PE2 and PF2alpha)
These locally diffuse from the uterus.
Cause small contractions of the myometrium.
Once released, the cervix is ready to be stretched.

Question 12

What kind of muscle is myometrium? Describe contraction of the myometrium. How is it triggered.

Answer 12

Smooth muscle.
Triggered spontaneously due to pacemakers in the body of the uterus.
The force generated is when intracellular calcium rises due to action potentials.
These create sustained contractions.

Question 13

What prevents labour occurring prematurely?

Answer 13

Progesterone

Question 14

Describe early uterine contractions in pregnancy.

Answer 14

Low amplitude, every 30 minutes

Mother may not be aware

Question 15

Describe uterine contraction in middle pregnancy.

Answer 15

Higher amplitude, less frequent.
Braxton-Hicks contractions.
Practice for labour

Question 16

How are the contractions of the uterus made more powerful and frequent?

Answer 16

Prostaglandins

• Increase intracellular calcium per action potential
• Stronger

Oxytocin

• More action potentials
• Lower threshold

Question 17

What are prostaglandins, where are they produced and how is production controlled?

Answer 17

Biologically active lipids.
Paracrine activity
Produced mainly in endometrium.
Production controlled by Oestrogen:Progesterone ratio.

P > O
- Low prostaglandins
- Throughout pregnancy
(remember P suppresses uterine contraction)

O > P

• Increased prostaglandins
• End of pregnancy

Question 18

Where is oxytocin secreted from?

Answer 18

Posterior pituitary, controlled by hypothalamus.

Question 19

What is the Ferguson Reflex?

Answer 19

Mechanical stimulation and pressure to the internal end of the cervix due to prostaglandin contractions increase oxytocin secretion.
These in run stimulate and strengthen contraction, stimulating the cervix more, releasing more oxytocin….
Until baby is delivered.

Question 20

What does oxytocin act on?

Answer 20

Smooth muscle receptors.

More receptors present if O > P.

Question 21

What is brachystasis?

Answer 21

Uterine smooth muscle relaxes less than it contracts.

This shortens the fibres in the body of the uterus over time and drives the fetus into the cervix.

Question 22

What happens to fetal cortisol, oestrogen, progesterone, prostaglandins, uterus, cervix and oxytocin at the end of pregnancy? What is the result?

Answer 22

Fetal cortisol Increased
Oestrogen > Progesterone
Increased prostglandins = stronger contractions.
Uterus contracts - fibres in body shorten.
Cervix is stretched.
Oxytocin increases continually by the Ferguson reflex.
Increased frequency of uterine contraction.
Cervix stretched more.
Labour initiated.

Question 23

What causes the fetus to take its first breath. What causes this?

Answer 23

Many stimuli, trauma, cold, light, noise

Reduced pulmonary vascular resistance due to increased arterial pO2

Question 24

What is the Apgar score?

Answer 24

Condition of the neonate assessment.
Assesses:
Colour, tone, pulse, respiration, response

Question 25

Why is the mother at risk of haemorrhage after birth?

Answer 25

Uterus continues to contract after neonate is born.

This shears of and expels the placenta, levying maternal vessels that ran into the placenta exposed.

Question 26

How is maternal blood loss limited after birth.

How can this be enhanced?

Answer 26

Continues uterine contraction compresses the blood vessels that run through the myometrium, closing them off and reducing haemorrhage.
This can be enhanced by giving an oxytocic drug.
Manual fundal massage - hand into vagina, fish down on fundus from external.

Question 27

What is the most common position in which a baby lies?

Answer 27

Longitudinally, in a cephalic presentation, well flexed so vertex present to pelvic inlet.
Diameter = 9.5cm

Question 28

Give the duration of pregnancy for spontaneous abortion, pre-term, term and post-term.

Answer 28

Spontaneous abortion - before 24 weeks
Pre-term - Before 36 completed weeks
Term - 37-42 weeks
Post-term - more than 42 weeks (likely baby dies in utero

Question 29

Describe contractions in early and late labour.

Answer 29

Early - variable but higher amplitude.

Late - more frequent and higher amplitude still.

Question 30

Describe how prostaglandin secretion is stimulated at the end of pregnancy.

Answer 30

As hCG falls at the end of pregnancy, progesterone falls relative to oestrogen, increasing prostaglandin secretion.

Question 31

What is effacement?

Answer 31

Cervical thinning and flattening

Question 32

What initiates labour?

Answer 32

Triggered by rise in O:P ratio
Placenta makes less P
Increased prostaglandins
Increased myometrial sensitivity to oxytocin.