Flashcards in Birth Deck (34):
What is the result of a decrease in the progesterone / oestrogen ratio?
1. Induction of parturition
2. Onset of labour
3. Increase in prostraglandin synthesis
How does the P:O ratio decrease?
Progesterone decreases and oestrogen increases
Human shows no prepartum decline in progesterone
What causes increased P450 C17 hydroxylase activity?
Increase in placental PGE2 synthesis
What increases placental PGE2 synthesis?
Prepartum rise in cortisol secretion by fetal adrenal glands
What is the sequence for the initiation of parturition?
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
What is the role of corticotrophin releasing hormone in parturition?
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
What are the three stages of labour?
1. Increasing uterine activity and cervical dilation
2. Expulsion of fetus
3. Expulsion of placenta
What factors influence timing of delivery?
1. Light/dark cycle
2. Food supply
What is the effect of growth and activation of the fetal adrenal in late gestation in humans?
Increases fetal availability of cortisol and DHAS
What is the result of increased DHAS production in late pregnancy?
Causes a rapid rise in maternal oestrogen levels close to term
What is the effect of increased oestrogen availability close to term?
Increased uterine contractility via enhanced PG synthesis
Is there evidence of removal of progesterone block to myometrial contraction in women?
What is the final common pathway to labour in all species?
Shortening of the uterine myocytes
What causes the increased expression of actin, myosin and other CAP proteins?
Rising oestrogen levels
Decreasing P:O ratio
What is the function of myosin light chain kinase in pregnancy?
Generates ATP for contraction of filaments in uterine myocytes to cause contractions
How is MLCK activated?
Calmodulin, which is in turn activated by calcium ions
How do intracellular calcium ion concentrations change during contractions?
Increase from 150nM to 500nM by increasing calcium influx through calcium channels and by releasing calcium stored in the sarcoplasmic reticulum
What are uterotonins?
Proteins that stimulate uterine contractions
Increase intracellular calcium
How is myometrial activity inhibited?
Inhibited calcium release from intracellular stores or by reducing MLCK activity
Mediated via cAMP or cGMP
How is contraction of myocytes coordinated?
Cell-to-cell coupling effected by formation of intercellular GAP junctions between adjacent myocytes
What influences expression of connexin proteins?
Steroids and mechanical stretch on the uterus
How do connexin numbers change at parturition?
Connexin abundance and the number of GAP junctions increase with the onset of labour
What are Braxton-Hicks contractions?
Contractions that precede labour
What occurs in the first stage of labour?
Increasing uterine activity and cervical dilatation
Cervix dilates to 10cm
Regular contractions force the baby's head down into the birth canal
How long does stage 1 of labour last?
10-12 hours in primagravida
6-8 hours in multigravida
What is the second stage of labour?
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
What is the most dangerous stage for the baby?
What is the third stage of labour?
Expulsion of placenta
Uterus continues to contract until the placenta and membranes are delivered
Lasts 10 minutes
What may happen if women retain pieces of placenta?
Risk of postpartum haemorrhage
What are the indications for induced delivery?
Waters have been broken for over 72 hours
Baby is overdue by 10 days
What are the indications for C section
Intrauterine growth restriction
What changes occur to maternal physiology in the first stage of labour?
Mild hyperventilation may produce light-headedness
Lowered circulating ionised calcium
What changes occur to the maternal physiology in the second stage of labour?
Breath holding and forced expiration against a closed glottis
Rise in blood pressure by 30/25mmHg can rupture a berry aneurysm