Repro: Parturition

Question 1

What is the difference between parturition and labour?

Answer 1

Parturition refers to birth
Labour is the part of parturition when both the cervix and uterus have been remodelled.
Parturition can occur without labour eg elective caesarian

Question 2

What classes as a ‘pre-term’ and ‘term’ fetus?

Answer 2

Pre-term is before 36 completed weeks. Term is 37-42 weeks.

Before 24 weeks is considered a spontaneous abortion as the fetus is not viable and has no legal rights.

Question 3

What is the risk of a post-term pregnancy?

Answer 3

(post-term is more than 42 weeks)
Increased risk of fetal death due to ureto-placental insufficiency, aspiration of meconium, macrosomia

At 42 weeks and 6 days the mother is at risk of death due to haemorrhage, infection, obstructed labour.

In UK the labour is induced at 41 weeks 3 days via a drug or rupture of the membranes.

Question 4

Broadly outline the 3 stages of labour

Answer 4

Stage 1: creation of the birth canal (cervix dilatation to 10cm and effacement)
Stage 2: expulsion of the fetus
Stage 3: expulsion of the placenta

Question 5

How does the rate of growth of the fetus relate to growth of the placenta?

Answer 5

The fetus and placenta should grow at the same rate. The placenta is weighed after birth and should be the same as the baby, if it is too small, too large or calcified the baby will need extra care.

Question 6

What assessments of fetal position need to be made towards the end of the pregnancy?

Answer 6

Lie: the relationship of the vertebral column of the fetus compared to the uterus. Usually longitudinal with the fetus in the flexed position.
Presentation: the part of the fetus that is adjacent to the pelvic inlet. Should be the crown, but can be the face, brow, feet (podalic / breech) or shoulder.
Vertex: relationship of fetus along its own axis, head should be 45 degrees from the vertebral column

Question 7

Why is a shoulder presentation particularly dangerous?

Answer 7

• risk of shoulder distocia, where the shoulders fail to deliver promptly after the head. Risk of brachial plexus injury
• risk of prolapse of the umbilical cord
• risk of impaction, the head will be at one iliac fossa and the bum at the other. With every contraction the fetus gets suffocated. Also risk of uterine rupture

Question 8

What is the typical diameter of the presentation and the birth canal?

Answer 8

Head is usually 9.5cm and pelvic inlet is 11cm - there is softening of the ligaments esp pubic symphysis which can give some increase.
If presentation is larger than pelvic inlet then emergency C section is needed

Question 9

What intervention can be used if the cervix is weakened and therefore there is risk of miscarriage of preterm labour?

Answer 9

Cervical cerclage - a tight suture put in and around the cervix to offer additional support

Question 10

What changes does the cervix undergo in the first stage of labour?

Answer 10

Effacement - the external os lines up with the internal os

Dilatation - from 1mm to 10cm

Question 11

What substances cause cervical ripening?

Answer 11

• Collagenases reduce collagen content
• Glycosaminoglycans separate the collagen strands to allow the ezymes in
• Increase in hyaluronic acid, expressed when 2 tissues rub together (head and cervix) which causes water influx to expand the tissue
• prostaglandins and oestrogen control the process

Question 12

What is the definition of clinical labour?

IMPORTANT

Answer 12

3 contractions in every 10 minutes lasting for at least 1 minute each

Question 13

Outline the uterine contractions throughout pregnancy

Answer 13

Early pregnancy: low amplitude contractions every 30 mins. Not detected

Mid pregnancy: less frequent but higher amplitude. May be detected - “Braxton-Hicks’ contractions. The uterus is preparing for labour to pull the fibres together

Early labour: variable and higher amplitude
Late labour: more frequent and higher amplitude

Question 14

How do oxytocin and prostaglandins affect contractions?

Answer 14

Oxytocin creates more action potentials by lowering the threshold
Prostaglandins cause more Ca2+ binding per action potential therefore the contractions are stronger

Question 15

How is the production of prostaglandins controlled?

Answer 15

The oestrogen: progesterone ratio

Oestrogen> progesterone causes increased prostaglandins which is why progesterone rapidly falls in the last month of pregnancy

Question 16

Outline the ferguson reflex

Answer 16

Stretch receptors in the cervix detect increased pressure which causes more oxytocin to be released which:

• stimulates the uterus to contract
• stimulates the placenta to make prostaglandins, which causes more contractions of the uterus which positively feedbacks to the placenta and the posterior pituitary.

The ovaries secrete oestrogen to increase the oestrogen:progesterone ratio which increases the number of smooth muscle receptors.

Question 17

What is brachystasis?

Answer 17

The uterus relaxes less than it contracts so the fibres shorten the body of the uterus. Creates a racketing system

Question 18

At what dilatation does the amnion usually rupture?

Answer 18

Around 2.5cm

Question 19

How long does the first, second and third stages of labour last?

Answer 19

First stage can last up to 96 hours
Second stage is up to an hour, any longer and the mother is exhausted
Third stage is normally 10 minutes (3 contractions)

Question 20

What is the term when 1 and 2 feet appear in the birth canal?

Answer 20

1 foot - footling breech

2 feet - double footling breech

Question 21

Describe the movement of the fetal head during the passage through the birth canal

Answer 21

Initially the head should be flexed (chin on chest)
The head the rotates 45 degrees so the chin is towards the shoulder
The head is delivered and extends so the fetus can pull itself out
The shoulders then rotate and deliver, quickly followed by the rest

This is because the inlet is longer in transverse and the outlet is longer in longitudinal so rotates the baby.

Question 22

Describe the third stage of labour

Answer 22

The uterus contracts down very hard, causing the placenta to be sheared off and expelled.
Tension is put on the umbilical cord and within 3 contractions (10 minutes) the placenta should be delivered

Question 23

What is the important effect of contraction of the uterus after parturition?

Answer 23

Compresses the spiral arteries which reduce haemorrhage. This can be enhanced by giving synthetic oxytocin

Question 24

What causes the baby to take its first breath?

Answer 24

Multiple stimuli such as trauma, cold, light and noise,

Crying shows that this has been achieved - baby must have inhaled to exhale

Question 25

What causes the ductus venosus to close?

Answer 25

Clamping of the umbilical cord

Question 26

What is the effect of progesterone on uterine contractions?

Answer 26

Inhibits contraction by reducing muscle excitability

Question 27

Where are prostaglandins synthesised?

Answer 27

The placenta, decidua (endometrium in pregnancy), myometrium and membranes

Question 28

Why does inducing labour before 34 weeks not work well?

Answer 28

Give oxytocin however until ~36 weeks the myometrium does not have many oxytocin receptors so the uterus does not respond well to the oxytocin

Question 29

Describe the properties of the contraction retraction response of the uterus

Answer 29

Contraction: the contractions are not symmetrical, the upper segment of the uterus contracts more powerfully than the lower segment in order to push the baby downwards.

Retraction: after each contraction the length of each myometrium muscle shortens, this decreases the capacity of the uterus and the pressure inside gets stronger and stronger

Question 30

What is the mucus plug?

Answer 30

Made up of the increasing levels of relaxin during pregnancy
It blocks the entrance of the cervix to prevent infections and falls out prior to labour.

Question 31

How does the cervix change throughout pregnancy?

Answer 31

Mid pregnancy the cervix is tubular and firm
Late pregnancy the head engages and the cervix softens due to oestrogen, prostaglandins and relaxin
Term the uterine contractions cause a dilated effaced cervix

Question 32

What potential obstructions are there in the passageway?

Answer 32

Pelvic inlet too small
Cervix can be stenosed if there is previous surgery or cancer
Vaginal polyps and masses

Question 33

What are the risks associated with a transverse lie?

Answer 33

There is a danger of the umbilical cord prolapsing causing the arteries to spasm, so no oxygen reaches baby
A C section should be done at term

Question 34

What is the latent and active phases of the first stage of labour?

Answer 34

Latent phase is the onset of labour with slow cervical dilatation (lasts up to ~4cm)

Active phase has a faster rate of cervical change, expect 1cm per hour with regular contractions

Question 35

What are the most common causes of maternal mortality?

Answer 35

(Pre)-eclampsia 25%
Postpartum haemorrhage 15%
Obstructed labour 10%
Unsafe abortion 10%
Ruptured uterus 5%

Question 36

How is the placenta delivered?

Answer 36

The continuing contractions squeeze the placenta which is inelastic, causing the spiral vessels to come away from the placenta and the venous blood is forced back into the decidua basilis
The veins become congested so blood cant drain back into the maternal blood stream

Question 37

Why is it so important to control haemorrhage?

How is this controlled?

Answer 37

Blood flow to the uterus during pregnancy is around 500-800ml/min so it is possible to lose this amount of blood per minute.
Give oxytocin (good but short lasting) and ergometrine (more sustained contraction) to contract the uterus. Also put pressure on uterus.