Labour

Question 1

What is spontaneous abortion?

Answer 1

Labour before 24 weeks

Question 2

What is pre-term labour classed as?

Answer 2

Before 37 weeks

Question 3

What is term labour classed as?

Answer 3

37-42 weeks

Question 4

What happens in general in each of the stages of labour?

Answer 4

First: creation of the birth canal
Second: expulsion of the fetus
Third: expulsion of the placenta, contraction of the uterus

Question 5

After how many weeks is the uterus palpable?

When does it reach the umbilicus?

When does it reach the xiphisternum?

Answer 5

12

20

36

Question 6

What is the lie of the fetus usually?

Answer 6

Fetus is normally flexed and longitudinal in relation to the long axis of the uterus

Question 7

What is the presentation of the fetus?

Answer 7

The head part is usually adjacent to the pelvic inlet (cephalic presentation)

Can sometimes be the buttocks (podalic presentation)

Question 8

What is the diameter of the head at presentation?

Answer 8

9.5cm

Question 9

What determines the maximum size of the birth canal?

Answer 9

The pelvis

Question 10

What is the diameter of the pelvic inlet?

Answer 10

Typically 11cm

Question 11

How is the birth canal created?

Answer 11

Expansion of soft tissues including the cervix, vagina and perineum to about 10cm

Question 12

What is the structure of the tough and thick cervix?

Answer 12

Collagen fibres embedded in a proteoglycan matrix

Question 13

Describe the process of cervical ripening (the structural changes)

Answer 13

Reduction in collagen production
Increase in glycosaminoglycans (GAGs) - disrupts the matrix
Reduces aggregation of collagen fibres so that they uncoil

Question 14

What stimulates cervical ripening?

Answer 14

Prostaglandins E2 and F2x which are locally diffused from the uterus

Question 15

How does the myometrium get bigger?

Answer 15

Smooth muscle cells increase in size 10 fold

Get glycogen deposition

Question 16

What generates force in the myometrium?

Answer 16

An action potential produced by the cells spontaneously depolarising causes an increase in intracellular calcium concentration

Question 17

How does the myometrium have a uterine contraction?

Answer 17

Action potentials can spread from cell to cell via gap junctions

Question 18

How do contractions of the myometrium change?

Answer 18

Early pregnancy - contractions of low amplitude every 30 minutes

As pregnancy continues, frequency falls and amplitude increases

Can cause Braxton-Hicks contractions

Question 19

What makes the contractions more forceful and frequent for labour and how?

Answer 19

Prostaglandins - more calcium per action potential

Oxytocin - more action potentials by lowering the threshold

Question 20

What are prostaglandins?

Answer 20

Biologically active lipids which act as local hormones

Question 21

What controls the production of prostaglandins?

Answer 21

Controlled by the progesterone:oestrogen ratio
-prog>oestrogen, prostaglandins low

Also stimulated by oxytocin

Question 22

What initiates labour?

Answer 22

Progesterone:oestrogen ratio decreases
-relative fall in progesterone
Get an increase in prostaglandins which ripen the cervix and promote uterine contractions

Question 23

How is response to oxytocin increased?

Answer 23

Fall in progesterone relative to oestrogen increases the oxytocin receptor population making cells more sensitive to low levels of oxytocin
(Oxytocin acts by binding to receptors on SMCs)

Question 24

What is the Ferguson reflex?

Answer 24

As contractions increase, sensory receptors in the cervix and vagina are stimulated by contractions and so get excitation via afferents nerves to the hypothalamus to increase secretion of oxytocin
-positive feedback

Question 25

Why is the Ferguson reflex good?

Answer 25

Increases frequency and force of contractions

Question 26

What is brachystasis?

Answer 26

On each contraction, muscle fibres shorten but do not relax fully Therefore the uterus, particularly the fundus, shortens progressively Pushes the presenting part into the birth canal and stretches the cervix over it - descent of presenting part

Question 27

What is thought to cause the fall in progesterone and increase in oestrogen to initiate labour?

Answer 27

Rising production of cortisol by the fetus as it matures | However some fetuses are born who don't produce cortisol

Question 28

Why does fetal heart rate need to be monitored during labour?

Answer 28

Uterine contractions can temporarily reduce placental blood flow, decreasing oxygen to the fetus Causes brief reductions in fetal heart rate If reductions in flow are greater than usual, get larger dips and the fetus becomes distressed

Question 29

When does the second stage of labour begin?

Answer 29

When cervical dilation reaches 10cm

Question 30

How long does the second stage of labour last?

Answer 30

1 hour in multiparous women | 2 hours in primigravida

Question 31

What is labour?

Answer 31

The expulsion of products of conception after 24 weeks

Question 32

Describe the positions of the fetus during the second stage of labour

Answer 32

Head flexes as it meets pelvic floor Internal rotation Sharply flexed head descends into vulva Head is delivered (crowning) As it emerges it rotates back to original position and extends Shoulders rotate, followed by head Shoulders delivered, followed by the rest

Question 33

What happens in the third stage of labour?

Answer 33

Powerful contraction of uterus Separates the placenta and positions in into the upper part of the Bahia and lower uterine segment Placenta and membrane then expelled in 10 mins

Question 34

Now is maternal blood loss reduced?

Answer 34

The massive uterine contraction also compresses the blood vessels and reduces bleeding Enhanced by gibing the oxytocic drug

Question 35

What triggers the fetus to take the first breath?

Answer 35

Drop in temperature | Delivery trauma

Question 36

What does the first breath cause?

Answer 36

Reduction in pulmonary vascular resistance Reduces pulmonary arterial pressure and increases left atrial pressure relative to right Closes the foramen ovale Rising pO2 causes ductus arteriosus to constrict, establishing the adult circulation Sphincter in ductus venosus constricts - blood to liver through hepatic sinusoids

Question 37

What is included in the Apgar score?

Answer 37

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