Labour And Delivery

Question 1

Define parturition.

Answer 1

Transition from pregnant to non-pregnant state.

Question 2

Define labour.

Answer 2

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

Question 3

Define delivery.

Answer 3

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

Question 4

What does labour involve?

Answer 4

Sequential integrated changes in the uterine decidua (internal lining) and myometrium.
Changes in the cervix occur following these uterine contractions.

Question 5

What are the 2 major end points of contractions in labour?

Answer 5

1. Dilatation of the cervix.

2. Pushing the fetus through the birth canal.

Question 6

What happens in the first stage of labour?

Answer 6

1. The creation of the birth canal.
2. Release of the structures which normally retain the fetus in utero.
3. Enlargement and realignment of the cervix and vagina.

Question 7

Define the first stage of labour physiologically.

Answer 7

Multiple changes resulting in creation of the birth canal and descent of the fetal head into it.

Question 8

When does the first stage of labour start and finish?

Answer 8

Onset of labour to full dilation of the cervix (10cm dilated).

Question 9

What are the 2 phases of the first stage of labour?

Answer 9

1. Latent: onset of labour with slow cervical dilatation but softening.
2. Active: faster rate of change and regular contractions.

Question 10

When does the uterus first become palpable?

Answer 10

12 weeks.

Question 11

Where has the fundus of the uterus reached at 20 weeks?

Answer 11

Umbilicus.

Question 12

Where has the fundus of the uterus reached by 36 weeks?

Answer 12

Xiphisternum.

Question 13

What is the lie of the fetus?

Answer 13

Describes the relationship of the long axis of the fetus to the long axis of the uterus.
Commonest longitudinal with head/buttocks posterior.
Fetus is normally flexed.

Question 14

What is the presentation of the fetus?

Answer 14

Describes which part of the fetus is adjacent to the pelvic inlet.
If fetus lies longitudinally presentation will be head or breach.
Presenting part have different diameter and thus is clinically significant in management.

Question 15

What is the diameter of presentation in a baby with cephalic presentation, well flexed and with vertex?

Answer 15

9.5cm

Question 16

How big is the birth canal in diameter?

Answer 16

10cm.

Question 17

What is the pelvic inlet bounded by?

Answer 17

1. Posterior: sacral promontory.
2. Lateral: ilio-pectineal line.
3. Anterior: superior rubic rami and pubic symphysis.

Question 18

What can allow the pelvic inlet to widen?

Answer 18

1. Softening of the pelvic ligaments.

2. Opening legs.

Question 19

What is needed to create a birth canal?

Answer 19

Cervix must dilate and be retracted anteriorly.

Question 20

What causes cervical ripening?

Answer 20

Amniotic fluid contains prostaglandin and this allows forceful contractions of uterine smooth muscle.

Question 21

What is cervical ripening?

Answer 21

Contractions cause thinning of the cervix (effacement) and dilation of the cervix.
The cervix changes: collagen decrease, GAGs increase, decreases aggregation of collagen fibres. Influx of inflammatory cells, and increased NO input from prostaglandins.

Question 22

What prostaglandins trigger cervical softening?

Answer 22

E2 and F2alpha.

Question 23

What happens to uterine smooth muscle?

Answer 23

Myometrium gets thicker (increased cell size and glycogen deposition). An intracellular apparatus contains actin and myosin, triggering a rise in intracellular calcium concentration, generating force. Rise in Ca conc produced from action potential.
Some smooth muscle cells are capable of spontaneous depolarisation and action potential generation (pacemakers).

Question 24

What happens in contractions throughout pregnancy?

Answer 24

Early pregnancy contractions happen every 30 minutes and low amplitude.
Pregnancy continues, frequency falls with some increase in amplitude-> Braxton-Hicks contractions.

Question 25

What 2 hormones cause increase frequency and fore of contraction?

Answer 25

1. Prostaglandins: enhance the release of calcium from intracellular stores.
2. Oxytocin: peptide hormone is secreted from the posterior pituitary gland under the control of neurons in the hypothalamus. Acts by lowering the threshold for triggering action potentials.

Question 26

What is the onset of labour associated with in terms of hormones?

Answer 26

Increased prostaglandin synthesis and release stimulating more forceful contraction is conjunction with increased sensitivity to oxytocin.

Question 27

Define the Ferguson Reflex.

Answer 27

Contractions increase, increasing release of oxytocin. Excitation passes via afferent nerves to the hypothalamus which promotes oxytocin release.

Question 28

What is Brachystasis?

Answer 28

Each contraction muscle fibres shorten but do not relax fully.
The uterus, particularly the fundal region will shorten progressively.
Pushes the presenting part into the birth canal and stretches the cervix over it.

Question 29

How is labour initiated?

Answer 29

Increase in prostaglandin production and oxytocin selectively triggered by a fall in progesterone levels relative to oestrogen.
Oestrogen and progesterone produced in placenta.
As labour progresses, increasingly forceful uterine contractions may temporarily reduce placental blood flow, so reduce oxygen supply to the fetus. Reduce fetal heart rate.

Question 30

When does the second stage of labour occur?

Answer 30

Cervical dilatation reaches 10cm- delivery of the fetus.

Question 31

How long does the second stage of labour typically last?

Answer 31

1 hour in multiparous woman.

2 hours in primigravida.

Question 32

What happens to the baby in the second stage of labour?

Answer 32

1. Descended head flexes as it meets the pelvic floor, reducing the diameter of presentation.
2. Internal rotation.
3. Sharply flexed head descends to the vulva, so stretching the vagina and perineum.
4. The head is delivered (crowning).
5. Emerges it rotates back to its original position and extends.
6. Shoulder rotate followed by head and shoulders deliver, followed by rest of fetus.

Question 33

What is Shoulder dystocia?

Answer 33

Fetal shoulder does not deliver without medical intervention, and can lead to complications for the mother and fetus.

Question 34

What happens in the third stage of labour?

Answer 34

When the fetus is removed there is a powerful uterine contraction, which separates the placenta. This positions the placenta into the upper part of the vagina or lower uterine segment.
Placenta and membranes are then expelled normally within about 10 minutes.
Contraction of the uterus also compresses the blood vessels.

Question 35

How does the fetus establish itself in independent life?

Answer 35

Foramen ovale closes due to decreased peripheral venous resistance and rising arterial pO2. This means the right pressure is lower than the left so foramen ovale closes.
Ductus arteriosus constricts due to the high arterial pO2.
Ductus venosus constricts so all the blood entering the liver passing through the hepatic sinusoids.

Question 36

How do you assess the neonate?

Answer 36

APGAR score.

Appearance, pulse, grimace, activity, respiration on a scale of 1-10. 10 being the most healthy.

Question 37

What are the 3 elements of labour clinically?

Answer 37

1. Power.
2. Passage.
3. Passenger.

Question 38

Describe the power in labour.

Answer 38

Depends on contraction of the myometrium that has undergone hypertrophy and hyperplasia. Contraction and retraction of the multidirectional smooth muscle fibres causes progressive shortening (fundus).

Question 39

How are uterine contractions assessed?

Answer 39

Frequency, amplitude and duration.

Question 40

Describe the passage in labour.

Answer 40

Passage formed by the bony pelvis and soft tissues.
Pelvic inlet is shorter in the anterior-posterior plane. Between the inlet and outlet it is circular.
Fetus flexes, extends and rotates as it passes through the birth canal.
Resistance of the soft tissue can slow labour.

Question 41

Describe the passenger in labour.

Answer 41

Size and presentation of the fetus is critical in labour.
Orientation of the head when entering the pelvis and variable head diameters and different positions determine the labour.
Moulding of the fetal cranium can occur since cranial sutures have not fused.