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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?

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


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
3. Infection
4. Climate
5. Danger/disturbance


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?

Cervical ripening

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?

Stage 2


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

Cephalic-pelvic disproportion

Intrauterine growth restriction

Previous C-section

Uterine damage


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


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

Oxytocin causes uterine contractions, which may still be painful

Risk of postpartum haemorrhage