Partuition

Question 1

What is the definition of parturition?

Answer 1

Parturition – The scientific term used to describe the transition from the pregnant state to the non-pregnant state at the end of gestation (i.e. birth).

Question 2

What is labour?

Answer 2

Labour – The non-scientific term used to describe parturition when both the cervix and uterus have been remodelled – Often used instead of ‘parturition’ because lay people also use it! Labour is a PART of parturition

Question 3

Describe when a baby is pre term, term and post term?

Answer 3

Spontaneous abortion - before 24 weeks
Pre-term - before 36 completed weeks
Term - between 37 and 42 weeks
Post-term - more than 42 weeks

Question 4

What are the 3 stages of labour

Answer 4

First stage – Creation of the birth canal
Second stage – Expulsion of foetus
Third stage – Expulsion of placenta – Contraction of uterus

Question 5

What weight is the placenta relative to the baby

Answer 5

Placenta should be about the same weight as the baby

Question 6

When does the foetus become palpable and when does it reach the umbilicus and xiphisternum?

Answer 6

At 12 weeks the uterus becomes palpable, reaches umbilicus at 20 weeks and Xiphisternum by 36 weeks.

Question 7

What is lie, presentation and vertex and what is most commonly seen for these three?

Answer 7

Lie
Relationship of foetal vertebrae to long axis of uterus, normally longitudinal and foetus normally flexed – arm crossed, legs folded up and chin on chest.

Presentation
Which part is adjacent to the pelvic inlet, normally head (cephalic) but sometimes buttocks (podalic) usually called breech, can also be face, brow or shoulder.

The vertex
The relationship of the foetus along its axis or the orientation of the presenting part. Most commonly they have a longitudinal lie, cephalic presentation and a vertex with a slightly twisted head so that it faces the pelvic inlet at minimum diameter.

Question 8

What is the normal size of a babies head and the birth canal?

Answer 8

In normal presentation – Head is the biggest part with a diameter of presentation of 9.5 cm. Maximum size of birth canal determined by pelvis – Pelvic inlet typically 11 cm – Softening of ligaments may increase this by collagenases.

Question 9

What is cervical ripening?

Answer 9

In the Cervix there is a large amount of collagen in the proteoglycan matrix. Ripening involves a reduction in collagen, increase in glycosaminoglycans, increase in hyaluronic acid and reduced aggregation of collagen fibres. This is triggered by prostaglandins – PGE2 and PGF2a. The increase in hyaluronic acid causes a movement of water into the matrix and eventually results in the cervix flattening out.

Question 10

How is a contractive force established?

Answer 10

Myometrium contains lots of smooth muscle which is thickened in pregnancy. When intracellular [Ca2+] rises, a contraction occurs due to action potentials which is triggered spontaneously by pacemakers located in the fundus of the uterus.

Question 11

Describe the differences in uterine contractions throughout pregnancy?

Answer 11

During Pregnancy
Early Low amplitude, every 30 min
Middle Less frequent than ‘real contractions’, Higher amplitude called ‘Braxton-Hicks’ contractions Labour – act to unify the fibres of the myometrium for the real thing

Labour
Early – variable but higher amplitude
Late – more frequent and higher amplitude still

Question 12

When is clinical labour?

Answer 12

Clinical labour – 3 contractions lasting a minute or more over a 10 minute period (EXAM)

Question 13

How are contractions modified by prostaglandins and oxytocin?

Answer 13

Contractions made more forceful and frequent by Prostaglandins which cause more Ca2+ per action potential. Oxytocin causes more action potentials by lowering threshold.

Question 14

Describe prostaglandins and their production in pregnancy

Answer 14

Biologically active lipids these are local hormones produced mainly in myometrium and decidua. Their production is controlled by oestrogen:progesterone ratio. Low (progesterone>oestrogen) causes low prostaglandins, high (oestrogen>progesterone) results in increased prostaglandins.

Question 15

What happens to progesterone at the end of pregnancy (generally)?

Answer 15

Towards the end of pregnancy there is a relative drop in progesterone that allows for ripening of the cervix and promotes uterine contractions.

Question 16

Describe the ferguson’s reflex?

Answer 16

Oxytocin is secreted by the posterior pituitary under control of the hypothalamus, oestrogen from the placenta controls the level of oxytocin in the pregnant woman. It acts on smooth muscle receptors and there are more receptors if oestrogen:progesterone ratio is high. Oxytocin is produced by the foetus and the mother. Oxytocin also stimulates the placenta to make prostaglandins which causes more contraction of the uterus and so oxytocin is increased by afferent impulses from Cervix and vagina due to stretch receptors – ‘Ferguson reflex’. (EXAM)

Question 17

Describe the role of prostaglandins during labour, what brachystasis is, when the waters breaks and what this all means for the uterus and cervix.

Answer 17

More prostaglandins so cervix ripens and uterine contractions become more forceful. Brachystasis - uterus relaxes less than contracts so fibres shorten in body of uterus driving presenting part to cervix.

Cervix thins and flattens (effacement). Ferguson reflex stimulates Oxytocin release causing contractions which become more forceful and more frequent. The cervix begins to dilate. During dulation rupture of the amnion occurs also known as breaking of the waters. The first stage ends after the cervix dilates to 10cm.

Question 18

Describe current understandings of the onset of labour

Answer 18

Prostaglandins promote labour but foetuses with no adrenals are still born (oestrogen stimulates prostaglandins). There is no consistent evidence of progesterone:oestrogen changes but there is evidence that surfactant protein A produced by foetal lungs causes prostaglandin production in the myometrium.

Question 19

Describe the second stage of labour and the terminology for when the presenting part of the baby isn’t correct

Answer 19

Relatively rapid – Up to 1 hour but can be very fast. Urge to ‘bear down’ and ‘push’ initiated. Presenting part appears in birth canal – If this is the top of the head then ‘crowning’ is correct term – If this is the buttocks, shoulder or knee then ‘breech presentation’ is the correct term – If this is a foot then ‘footling breech’ is the correct term.

Question 20

What happens to the position of the foetus as it passes through the birth canal?

Answer 20

During crowing the foetal head flexes and rotates internally. As the head passes through the birth canal the vagina and perineum becomes stretched and there is a risk of tearing. After the head is delivered it rotates and extends, the shoulders rotate and are delivered followed rapidly by the rest of the foetus.

Question 21

What is the third stage of labour?

Answer 21

Placenta left attached to baby to allow the remaining blood to be pumped into the baby. The effect of uterine contractions are dramatically increased by expulsion of foetus. The uterus contracts down hard and shears off the placenta expelling it. Normally occurs within 10 minutes.

Question 22

What are the importance of uterine contractions in the third stage of labour and how do we assist this?

Answer 22

Importance of uterine contractions are that they compress blood vessels to reduce haemorrhage. This is enhanced by giving oxytocic drug and also manual fundal massage.

Question 23

How is independent life established?

Answer 23

Neonate takes first breath because of multiple stimuli: trauma, cold, light, noise. This first breath results in reduced pulmonary vascular resistance and so ventilation begins increasing arterial pO2.

Net drop in pressure on the right side of the heart, higher pressure in left atrium closes Foramen ovale. This pressure imbalance results in a temporary reversal of flow through the Ductus arteriosus and its muscle wall contracts in response to increased pO2 closing it

Placenta cut or clamped so ductus venosus closes. Left atrial pressure exceeds right – Foramen ovale closes. Ductus arteriosus contracts in response to raised pO2 (Normally Ductus arterious closes).