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Describe the four stages of labour and birth?

Stage 1: uterine contractions are of sufficient frequency, intensity and dueration to cause effacement and dilation of the cervix.
Stage 2: begins with the complete dilation of the cervix and ends with the birth of the baby;
Stage 3: the birth of the placenta;
Stage 4: the first hour or two after the birth of the placenta when uterine tone is established and recovery from labour begins.


Placental Corticotrophin-releasing hormone (CRH) appears to have a dual role. What are these two roles?

During pregnancy it encourages inactivity of the uterine muscles, however, during labour, under the influence of oxytocin, it binds to different receptor types and promotes uterine contraction.


How do Placental Corticotrophin-releasing hormone (CRH) levels change during pregnancy?

They increase significantly after 35 weeks, and then decrease sharply within 20 - 30 mins of birth.

Levels are higher in cases of preterm labour, and in pregnancies complicated by hypertension and IUGR, both of which can result in preterm labour.


What are prostaglandins?

Lipids that are synthesised in tissues throughout the body. They are local hormones (paracrine hormones) which act at or near the place where they are synthesised. They are directly responsible for uterine contractions. They also play a role in softening the cervix, enabling effacement and dilation.


What gland releases oxytocin?

Posterior pituitary.


What triggers the release of oxytocin from the posterior pituitary?

Tactile stimulation of the reproductive tract, in particular, the cervix. This is known as the Ferguson reflex.


The majority of oxytocin is released from the posterior pituitary. What other structures release this hormone?

Local (paracrine) release of oxytocin is made from the fetal membranes, the decidua and the placenta.


How does oestrogen facilitate myometrial contractility?

It increases the sensitivity of the myometrial oxytocin receptors.


Elevated levels of oestriol are associated with ...?

The onset of labour.


Which hormone supresses uterine excitability during pregnancy?



Relaxin is produced by ... ?

the myometrium, the decidua and placenta.


What produces Nitric Oxide?

Decidua, fetal membranes, and fetal and placental vasular epithelium.


Why is Nitric Oxide important?

It is important in reducing uterine contractility in pregnancy, and may play a role in cervical ripening.