13. Labour And Delivery

Question 1

What is the definition of parturition?

Answer 1

Transition from pregnant to non-pregnant state (birth).

Question 2

What is the definition of labour?

Answer 2

Physiologic process by which a fetus is expelled from the uterus to the outside world.

Question 3

What is the definition of delivery?

Answer 3

The method of expulsion of the fetus, transforming the fetus to neonate.

Question 4

What are the two main aims of contractions in labour?

Answer 4

Dilation of the cervix and pushing the fetus through the birth canal.

Question 5

What is the birth canal formed from?

Answer 5

Bone - pelvic minor.

Soft tissue - uterus, vagina, external reproductive organs.

Question 6

What happens physiologically and clinically in the first stage of labour?

Answer 6

Physiologically - multiple changes resulting int he creation of the birth canal and descent of the foetal head into it.
Clinically - interval between onset of labour (waters breaking) and full dilation of the cervix.

Question 7

What are the 2 phases of the first stage of labour, and what happens in each?

Answer 7

Latent - onset of labour with slow cervical dilation but softening. Lasts a variable time.
Active - factor rate of change (cervical dilation from 3/4cm to 10cm) and regular contractions.

Question 8

What happens physiologically and clinically in the second stage of labour?

Answer 8

Physiologically - changes in uterine contractions to expulsive, descent of the fetus through the birth canal and delivery.
Clinically - time between the full dilation of the cervix and delivery.

Question 9

What are the two phases of the second stage of labour, and what happens in each?

Answer 9

Passive - descent and rotation of the head.

Active - maternal effort to expel the fetus and achieve birth.

Question 10

What happens physiologically and clinically in the third stage of labour?

Answer 10

Physiologically - expulsion of the placenta and contraction of the uterus.
Clinically - starts with the completed birth of the baby and ends with complete expulsion of the placenta and membranes.

Question 11

What is the normal length of the third stage of labour?

Answer 11

15-30 minutes. Up to 30-60 minutes may be normal depending on circumstances and management (over 60 minutes definitely not normal).

Question 12

What are the two main biochemical steps involved in initiating labour and what do they cause?

Answer 12

Prostaglandins produced in the myometrium and decidua due to decrease in progesterone and increase in oestrogen - cause softening and shortening of the cervix and maintain uterine contractions.
Oxytocin acts on uterus via increased number of oxytocin receptors in myometrium - initiates uterine contractions.

Question 13

What happens to the uterine musculature once labour begins to allow contractions?

Answer 13

Becomes progressively more excitable.

Question 14

What hormone inhibits contractions?

Answer 14

Progesterone.

Question 15

What hormone increases gap junctional communication between smooth muscle cells of the uterus, thus increasing contractility?

Answer 15

Oestrogen.

Question 16

What affect on contractility does mechanical stretching of the uterine smooth muscle have as gestation increases?

Answer 16

Increases contractility.

Question 17

Why would you give anti-progesterone to someone who has lost their baby?

Answer 17

To induce labour.

Question 18

Where is oxytocin secreted from?

Answer 18

Posterior pituitary (controlled by the hypothalamus).

Question 19

What causes increase in oxytocin release?

Answer 19

Afferent impulses from the cervix and vagina (ferguson reflex).

Question 20

What is the structure of the cervix like for most of pregnancy?

Answer 20

Tough, thick and collagenous to retain the fetus - is a collagen in proteoglycan matrix.

Question 21

What happens physiologically in cervical ripening?

Answer 21

Reduction in collagen, increase in glycosaminoglycans, increases in hyaluronic acid, reduced aggregation of collagen fibres, increased water in spaces created.

Question 22

Under the influence of what two hormones does cervical ripening occur?

Answer 22

Prostaglandins and relaxin.

Question 23

Over what time frame does cervical ripening occur?

Answer 23

36-40 weeks.

Question 24

What clinically happens to the cervix in cervical ripening?

Answer 24

Effacement and dilation.

Question 25

What 2 things is the maximum size of the birth canal determined by?

Answer 25

Pelvic inlet, and degree of softening of ligaments under the influence of oestrogen and progesterone.

Question 26

What changes occur to the pelvic floor, vagina and perineum during labour?

Answer 26

Stretching of the fibres of the levator ani and the thinning of the central portion of the perineum transforms to almost a transparent membranous structure.

Question 27

What happens to myometrial fibres when hey contract?

Answer 27

Contract and only partially relax, leading to permanent shortening of the muscle fibres and therefore contraction and retraction.

Question 28

In what pattern do uterine contractions occur?

Answer 28

Create two poles of the uterus, to fundus, upper part of uterus, down to lower segment.

Question 29

A rise in what ion leads to increased myometrial force in labour?

Answer 29

Rise in intracellular [Ca2+].

Question 30

What specific effect do prostaglandins and oxytocin have on contractions?

Answer 30

Prostaglandins - increase Ca2+ per action potential so more forceful contractions.
Oxytocin - lower the threshold for action potentials, so more action potentials.

Question 31

What are the 3 aspects of foetal presentations?

Answer 31

Lie - longitudinal and transverse.
Attitude - flexion and extension of head.
Presentation - frank breech, full breech, single footing breech, non breech.

Question 32

How is labour artificially induced?

Answer 32

Rupture membrane - stimulate release of prostaglandins.
Give artificial prostaglandins - stimulate cervical ripening.
Give synthetic oxytocin - initiate uterine contractions.
Give anti-progesterone agents.

Question 33

Give 3 ways in which the physiology of the fetus can be monitored during labour

Answer 33

Heart rate patterns (using USS, foetal stethoscope).
Maternal temperature.
Colour and amount of amniotic fluid.
Scalp capillary pH.

Question 34

What happens anatomically to the positions of the baby during the second stage of normal labour?

Answer 34

1. Head flexes - present minimum diameter.
2. Head rotates internally.
3. Head stretches perineal muscle and skin - crowning.
4. Extension of the head and external rotation/restitution.
5. Shoulder rotate, deliver and are followed rapidly by the body.

Question 35

Give 2 ways that delivery can be facilitated by intervention

Answer 35

Caesarean section.
Forceps.
Vacuum extraction.

Question 36

What position should the baby enter the birth canal in?

Answer 36

Occipital anterior.

Question 37

What leads to reduction in the size of the placental site straight after birth of the baby?

Answer 37

Reduction in size of the uterus due to powerful contraction and retraction - the inelastic placenta is squeezed by contraction.

Question 38

What leads to the expulsion of the placenta?

Answer 38

Myometrium contracts and causes separation of the placenta from the uterus, pushing it down and out.

Question 39

What 3 things control the bleeding from the placental site when the placenta is delivered?

Answer 39

Powerful contraction/retraction of the uterus and action of interlacing muscle fibres, which constrict blood vessels running through the myometrium (living ligature).
Pressure exerted on placental site by walls of the contracted uterus.
Blood clotting mechanism.

Question 40

What is normal blood flow through the placental site?

Answer 40

500-800 ml/minute.

Question 41

What helps to obliterate the cavity of the uterus?

Answer 41

Contraction of deliver the placenta.

Question 42

What causes the neonate to take its first breath?

Answer 42

Stimuli - trauma, cold, light, noise.
Reduced pulmonary vascular resistance.
Increased arterial pO2.