Birth

Question 1

What is the result of a decrease in the progesterone / oestrogen ratio?

Answer 1

1. Induction of parturition
2. Onset of labour
3. Increase in prostraglandin synthesis

Question 2

How does the P:O ratio decrease?

Answer 2

Progesterone decreases and oestrogen increases

Human shows no prepartum decline in progesterone

Question 3

What causes increased P450 C17 hydroxylase activity?

Answer 3

Increase in placental PGE2 synthesis

Question 4

What increases placental PGE2 synthesis?

Answer 4

Prepartum rise in cortisol secretion by fetal adrenal glands

Question 5

What is the sequence for the initiation of parturition?

Answer 5

1. Fetal pituitary signals to fetal adrenal
2. Fetal adrenal increases cortisol and DHAS secretion
3. Cortisol causes maturation of tissues
4. Cortisol and DHAS cause placenta and membranes to secrete more oestrogen
5. Increased oestrogen causes PGF2 synthesis
6. Myometrial contraction, cervical ripening

Question 6

What is the role of corticotrophin releasing hormone in parturition?

Answer 6

Placental product

Coordinates labour

1. Acts on fetal adrenal to increase DHAS secretion
2. Acts on uteroplacental tissues to increase PG availability
3. Acts on myometrium to inhibit contractions by increasing cAMP

Question 7

What are the three stages of labour?

Answer 7

1. Increasing uterine activity and cervical dilation
2. Expulsion of fetus
3. Expulsion of placenta

Question 8

What factors influence timing of delivery?

Answer 8

1. Light/dark cycle
2. Food supply
3. Infection
4. Climate
5. Danger/disturbance

Question 9

What is the effect of growth and activation of the fetal adrenal in late gestation in humans?

Answer 9

Increases fetal availability of cortisol and DHAS

Question 10

What is the result of increased DHAS production in late pregnancy?

Answer 10

Causes a rapid rise in maternal oestrogen levels close to term

Question 11

What is the effect of increased oestrogen availability close to term?

Answer 11

Cervical ripening

Increased uterine contractility via enhanced PG synthesis

Question 12

Is there evidence of removal of progesterone block to myometrial contraction in women?

Answer 12

NO

Question 13

What is the final common pathway to labour in all species?

Answer 13

Shortening of the uterine myocytes

Question 14

What causes the increased expression of actin, myosin and other CAP proteins?

Answer 14

Rising oestrogen levels

Decreasing P:O ratio

Question 15

What is the function of myosin light chain kinase in pregnancy?

Answer 15

Generates ATP for contraction of filaments in uterine myocytes to cause contractions

Question 16

How is MLCK activated?

Answer 16

Calmodulin, which is in turn activated by calcium ions

Question 17

How do intracellular calcium ion concentrations change during contractions?

Answer 17

Increase from 150nM to 500nM by increasing calcium influx through calcium channels and by releasing calcium stored in the sarcoplasmic reticulum

Question 18

What are uterotonins?

Answer 18

Proteins that stimulate uterine contractions

Increase intracellular calcium

Question 19

How is myometrial activity inhibited?

Answer 19

Inhibited calcium release from intracellular stores or by reducing MLCK activity

Mediated via cAMP or cGMP

Question 20

How is contraction of myocytes coordinated?

Answer 20

Cell-to-cell coupling effected by formation of intercellular GAP junctions between adjacent myocytes

Question 21

What influences expression of connexin proteins?

Answer 21

Steroids and mechanical stretch on the uterus

Question 22

How do connexin numbers change at parturition?

Answer 22

Connexin abundance and the number of GAP junctions increase with the onset of labour

Question 23

What are Braxton-Hicks contractions?

Answer 23

Contractions that precede labour

Question 24

What occurs in the first stage of labour?

Answer 24

Increasing uterine activity and cervical dilatation

Cervix dilates to 10cm

Regular contractions force the baby’s head down into the birth canal

Question 25

How long does stage 1 of labour last?

Answer 25

10-12 hours in primagravida 6-8 hours in multigravida

Question 26

What is the second stage of labour?

Answer 26

Expulsion of fetus Requires voluntary effort as well as uterine contractions Baby needs to engage, flex and rotate Lasts 45-120 minutes in primigravida 15-45 minutes in multigravida

Question 27

What is the most dangerous stage for the baby?

Answer 27

Stage 2

Question 28

What is the third stage of labour?

Answer 28

Expulsion of placenta Uterus continues to contract until the placenta and membranes are delivered Lasts 10 minutes

Question 29

What may happen if women retain pieces of placenta?

Answer 29

Risk of postpartum haemorrhage

Question 30

What are the indications for induced delivery?

Answer 30

Waters have been broken for over 72 hours Baby is overdue by 10 days

Question 31

What are the indications for C section

Answer 31

Cephalic-pelvic disproportion Intrauterine growth restriction Previous C-section Uterine damage

Question 32

What changes occur to maternal physiology in the first stage of labour?

Answer 32

Mild hyperventilation may produce light-headedness Lowered circulating ionised calcium

Question 33

What changes occur to the maternal physiology in the second stage of labour?

Answer 33

Breath holding and forced expiration against a closed glottis Rise in blood pressure by 30/25mmHg can rupture a berry aneurysm

Question 34

What changes occur to the maternal physiology in the third stage of labour?

Answer 34

Oxytocin causes uterine contractions, which may still be painful Risk of postpartum haemorrhage