Cause, Onset and induction of Labour Flashcards
Definition of labour
The process whereby uterine contractions are accompanied by effeacement and dilatation of the cervix, resulting in expulsion of products of coneption
How to diagnose labour
Labour commences when uterine contractinos of sufficient frequency, intensity and duration 1:10 for 1 hour result in cervical dilationof at least 2cm and effecement
What causes labour
The start of labour occurs when those factors which inhibit contractions and maintain a closed cervix diminish and are succeeded by the action of factors which do the opposite
Around 32 wks, oestrogen rises faster than progesterone
What are the functions of oestrogen
- Reduces the inhibitory actions of progesterone
- Stimulates increase production of prostaglandin
- Increases actin and myosin
- Upregulates oxytocin receptors
What is the function of prostaglandins E2 (PGE2)
- Dilation of small vessels in the cervix
- Increase in hyaluronic acid
- Increase production of hyaluronidase, elastase, collagenase and matrix metalloproteinase 2 & 9
- Increase in stimulation of interleukin (IL)–8 release (mediator)
What is the function of oxytocin
Stimulates uterine contractions
What is the function of cortisol
Stimulates increased oestrogen production from the placenta
What is Ferguson
The Ferguson reflex is a positive feedback mechanism whereby the female’s body responds to pressure applied to the cervix and vaginal walls causing increased release in oxytocin from the maternal posterior pituitary (neurohypophysis)
This in turn causes more contractions until the baby is delivered
What is the cervix made of and maintains it?
Type 1 & type 3 collagen, also some type 4
Glycosaminoglycans (dermatan sulfate, hyaluronic acid) and proteoglycans (heparin sulfate)
Fibronectin and elastin
How is the cervix ripened?
Prostaglandins
Hyaluronic acid increases - water content increases
Dermatan sulphate decreases - firmness decreases
Indications for labour induction
Post-term pregnancy
Pre-eclampsia and Hypertensive disorders of pregnancy
Diabetes Mellitus
Prelabour rupture of membranes (PROM) & Preterm prelabour rupture of membranes (PPROM)
Foetal Macrosomia
Indications for labour induction
Rhesus Immunization Sickle cell disease Foetal growth restriction Twin pregnancy continuing beyond 38 weeks Deteriorating maternal illness Unexplained antepartum haemorrhage ‘Social’ reasons
Absolute contraindications for labour induction
A major placenta praevia or a vasa praevia Abnormal foetal lie Umbilical cord prolapse Previous transfundal uterine surgery Cephalo-pelvic disproportion
Relative contraindications for labour induction
Previous lower segment caesarean section Grand multiparity Polyhydramnios Multifetal pregnancy Maternal cardiac disease
Pharmacological methods of labour induction
Oxytocin - when cervix is favourable
PGE1 & E2
PGE2 - dinoprostone gell (Prostin) 1-2mg and dinoprostone pessary (Cervidil) 10mg slow release
Misoprostol (PGE1) - when cervix is not favorable Bishop score <6
