Labour Vivian Phan

3 stages of labour 1. Creation of birth canal – Start: sudden increase in frequency & force of contractions (hormones?) – Finish: cervix is 10cm dilated 2. Delivery of fetus – Finish: baby’s out! 3. Delivery of placenta & management of blood loss

Hormones PROSTAGLANDINS (E2, F2x) -Induce labour -Increase release of intracellular Ca -> contractions -Lipids, produced mostly by endometrium -Triggered by  Progesterone: Oestrogen OXYTOCIN -Produced in posterior pituitary gland (HPO axis) -Receptors on uterine smooth muscle cells -  Progesterone: Oestrogen increase receptor numbers -> more sensitive to Oxytocin -Lower threshold for action potentials -> contractions

1 st Stage Cervical ripening/ softening: triggered by PGD –  collagen;  GAGs -> “loosen” collagen bundles – Inflammatory cells ->  Nitric oxide Ferguson reflex: +ve feedback loop Contractions -> sensory receptors in cervix & vagina -> hypothalamus ->  Oxytocin release ->  force & freq of contractions Brachystasis Uterine smooth muscle fibres shorten with each contraction -> uterus progressively shortens -> push presenting part of fetus out & dilate cervix over it

2 nd Stage 10cm dilation -> delivered fetus Episiotomy 3 rd Stage Powerful contractions -> shearing of placenta, compress blood vessels, reduce bleeding 10-20mins after baby’s out Oxytocin drug

Problems POWERS: uterine contractions PASSAGE: bony pelvis + soft tissue PASSENGER: size + presentation of fetus