Repro 10: Parturition

Question 1

What is parturition?

Answer 1

The expulsion of the products of conception after 24 weeks (transition from pregnant to non-pregnant state at the end of gestation)

Question 2

How is labour different to parturition?

Answer 2

Non scientific lay man term

Labour is part of parturition, describes when both the cervix and uterus has been remodelled

Question 3

Which weeks of gestation classes a baby as being born at term?

Answer 3

37-42 weeks

Spontaneous abortion before 24 weeks, pre term before 36 weeks, and post term after 42 weeks

Question 4

What briefly happens in each stage of labour?

Answer 4

1st: creation of birth canal
2nd: expulsion of foetus
3rd: expulsion of placenta and contraction of uterus

Question 5

What should the lie of the foetus be?

Answer 5

Should be longitudinal to the long axis of the uterus

Question 6

What should the attitude and presentation of the foetus ideally be?

Answer 6

Normally flexed, and in cephalon presentation (head in pelvic inlet)

Question 7

What is the term used for a foetus in a podalic presentation (feet and buttocks in pelvic inlet)?

Answer 7

Breech

Question 8

What is the vertex of a foetus?

Answer 8

It’s orientation to the pelvic inlet at minimum diameter, ie head down position ideally 9.5cm

Question 9

When is the uterus usually first palpable?

Answer 9

Approx 12 weeks

Question 10

When can the uterus usually be palpated at the xiphisternum?

Answer 10

Approx 36 weeks

Question 11

What is effacement?

Answer 11

Thinning of the cervix ready to create the birth canal

Question 12

How is cervical ripening initiated?

Answer 12

Reduction in collagen
Increase in glycosaminoglycans (GAGs which decrease aggregation of collagen fibres)
Increase in hyaluronic acid (hydrophilic so can form blisters)
Increase in NO

Question 13

What triggers cervical ripening?

Answer 13

Prostaglandins (E2 and F2x)

Question 14

How does the myometrium generate the force for its contractions?

Answer 14

Increase in intracellular Ca2+ caused by action potentials that can spread from cell to cell, allowing coordinated contractions
Some smooth muscle cells can spontaneously depolarise and act as pacemakers

Question 15

When do uterine contractions occur in pregnancy?

Answer 15

Occur throughout pregnancy, just start at a low amplitude and increase towards the end (higher amplitude towards the end are Braxton Hicks contractions, which give the impression of false labour)

Question 16

When in clinically labour defined?

Answer 16

3 contractions last one minute or more, within a 10 minute interval

Question 17

What initiates the sudden increase in frequency and force of contractions at the onset of labour?

Answer 17

Prostaglandins and oxytocin

Prostaglandins enhance the release of Ca from intracellular stores, oxytocin lowers the threshold to trigger APs

Question 18

How does the oestrogen: progesterone ratio change to increase prostaglandins?

Answer 18

Oestrogen > progesterone

Question 19

What is the Ferguson reflex?

Answer 19

Positive feedback mechanism
As sensory receptors in cervix and vagina are stimulated by contractions, excitation passes via afferent nerves to the hypothalamus and promotes more oxytocin release, so contractions become even more more forceful and frequent

Question 20

Where is oxytocin released from?

Answer 20

The posterior pituitary gland, controlled by the hypothalamus

Question 21

What is brachystasis?

Answer 21

Describes that with each contraction, the uterus muscle fibres shorten and relax less
So the fundus region shortens progressively which pushes the presenting part of the foetus into the birth canal, stretching the cervix over it

Question 22

How long does the second stage of labour usually take?

Answer 22

Usually rapid, about 1 hour (up to two hours in primigravida)

Question 23

How does the position of the foetus change during the second stage of labour?

Answer 23

Presenting part of foetus appears in birth canal (crowning)
Head flexes and rotates internally, then rotates and extends and is delivered
Shoulder rotate and deliver, followed by rest of foetus

Question 24

What occurs in the third stage of labour?

Answer 24

A powerful uterine contraction shears the placenta and expels it, usually within 10 minutes
Uterus contraction also compressed blood vessels to reduce haemorrhage

Question 25

How can the compression of blood vessels in the uterus be enhanced in the third stage of labour to reduce haemorrhage?

Answer 25

By oxytocic drug, or manual fundus massage

Question 26

How does the foetus establish independent life when first born?

Answer 26

Takes its first breath
Pulmonary vascular resistance lowers
Increases in pO2 causes ductus arteriosus to constrict
Higher pressure in LA to RA causes foramen ovalae to shut
Clamping of umbilical cord shut the ductus venosus

Question 27

What is the Apgar score?

Answer 27

Used to assess neonate condition when first born