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Flashcards in Repro 10 Deck (61)
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When is labour viable?

After 24 weeks. Before this, it is spontaneous abortion. Before 37 weeks, birth is pre-term or premature.


Where does the uterus extend to by 36 weeks?



How wide is the girth of the umbilicus of the mother at 24 weeks?

60cm. After this, the girth increases by approximately 2.5cm per week until term at which point it is approximately 100cm.


How is the period of the first stage of labour defined?

Interval between the onset of labour and full cervical dilation


What are the phases of the first stage of labour?

Latent: Slow cervical changes to approx 4cm dilation. Varying duration
Active: Faster rate of cervical change - 1-1.2cm/hr with regular uterine contractions


What is the lie of the foetus?

The relationship of the foetus long axis to the long axis of the maternal uterus. Should be parallel - longitudinal.


What is the presentation of the foetus?

Describes which part is adjacent to the pelvic inlet. Usually head (cephalic) or buttocks (podalic) aka breech. Presenting part may be in a variety of positions.


What does the clinical management of labour depend on?

Lie and presentation of the foetus


What is the typical position of the presenting part of the foetus?

Flexed - vertex presents to the pelvic inlet. In this case, diameter of presentation is typically 9.5cm


What is the required diameter of the birth canal?



What limits the diameter of the birth canal?

Pelvic inlet:
Bound posteriorly by the sacral promontory, laterally by the ilio-pectinal line and anteriorly by the superior pubic rami and the upper margin of the pubic symphysis.


What usually the true diameter of the pelvic inlet?



How might the diameter of the pelvic inlet be increased?

Softening of the pelvic ligaments may allow some expansion


How is the foetus normally retained in the uterus?

The cervix is closed and relative quiescence of the myometrium


How is the birth canal created?

Cervix dilates and is retracted anteriorly


What process is seen exteriorly as the "waters breaking"?

Foetal membrane rupture releasing amniotic fluid. This occurs at some point during dilation and retraction of the cervix


How does cervical dilation occur?

Cervical ripening (structural changes) facilitate it and forceful contractions of the uterine smooth muscle cause effacement and then dilation


Why is cervical ripening required?

Would tear without these structural changes.


When does cervical ripening occur?

From 36 weeks


What changes occur in the cervix during ripening?

Marked reduction in collagen and marked increase in glycosaminoglycans (GAGs) which decrease the aggregation of collagen fibres. Keratin sulphate increases at the expense of derma ton sulphate. Consequently, collagen bundles loosen.
Influx of inflammatory cells and increase in nitric oxide output.


What triggers cervical ripening?

Prostaglandins, namely E2 and F2x


How does the myometrium size change during pregnancy?

Becomes much thicker, primarily due to increased cell size (10 fold) and glycogen deposition


What causes the co-ordinated contractions of the myometrium?

Action potentials spread from cell to cell via specialised gap junctions. Some sm cells are capable of spontaneous depolarisation and action potential so can act as pacemakers.


Where are the pacemakers in the myometrium?

In the top of the uterus at the poles. Spreads to fundus and then down. More powerful contraction at the top than the bottom.


What effect does oestrogen have on the smooth muscle cells of the myometrium?

Increases gap junction communication between smooth muscle cells, increasing contractility.


When do contractions of the myometrium begin?

Always spontaneously active. In early pregnancy, may occur every 30 mins but at low amplitude so not felt (maybe flutter). As pregnancy continues, the frequency falls but with some increase in amplitude, potentially producing noticeable contractions - Braxton-Hicks' contractions. None of these contractions are normally forceful enough to have any effect on the foetus but can induce pain and be mistaken for labour.


What causes the onset of labour?

Prostaglandins and oxytocin.


What are prostaglandins?

Lipid paracrine hormones


What is the function of prostaglandins in labour?

Enhance the release of calcium from intracellular stores


Where are prostaglandins produced?

Mostly endometrium
Also myometrium, decidua and placenta
Amnion increases prostaglandin release in 3rd trimester