Parturition Flashcards
Labour
Physiological process by which foetus, placenta and membranes are expelled through the birth canal after viability of the foetus (22 weeks gestation). Characterised by regular and painful uterine contractions with cervical changes (effacement and dilatation) that concludes in progressive labour.
Physiology of Labour
- Corticotrophin-releasing hormone (CRH) from the foetal hypothalamus stimulates release of Adrenocorticotropic Hormone (ACTH) from the foetal pituitary. This acts on the foetal adrenal gland which releases cortisol to act on the placenta and secrete oestrogens.
- When cortisol binds to the receptors in the placenta, it causes an increase in interleukins 1, 6 and 8, decrease in progesterone, increase in oestrogen, increase in prostaglandins and increase in oxytocin. It also causes a release of CRH which acts on the foetal hypothalamus, creating a loop.
- Meanwhile in the mother, the oxytocin production leads to increase in myometrial receptors (prostaglandins and oxytocin), increase in gap junction, increase in decidual prostaglandin F2 and increase stretch receptor number and sensitivity. Leads to uterine contractions and labour.
Preterm Gestation Period
24-37 weeks gestation
Term Gestational Period
37-42 weeks gestation
Post term Gestational Periods
after 42 weeks gestation
Estimated Date of Delivery
- dates or scan (Last menstrual period (first day of last period) + 9 months + 7 days)
- 280 days (40 weeks)
Fundal Height
Fundal height is measured in cm from the pubic crest to the top most portion of the uterus. After 20 weeks, it often matches the number of weeks you have been pregnant.
Foetal Lie/Presentations
- Longitudinal Lie - Vertex or Breech presentation
- Oblique lie
- Transverse lie - shoulder presentation
- Abnormal presentations include face, brow, breech and shoulder.
- Cephalic lie - most normal presentation with occiput presenting first at pelvis.
Diagnosis of Labour
- History - labour pains, show, sudden loss of fluid from vagina.
- Abdo exam - uterine contractions: frequency (3/10), duration (40-60s), severity (pressure >80mmHg).
- Pelvic exam - cervical dilatation, effacement, consistency, position, level of presenting part.
Stages of Labour
- 0 - Quiescent uterus - maintained by progesterone and relaxin - inhibitors: progesterone, prostacyclin, relaxin, nitric oxide, parathyroid hormone-related peptide (corticotropin-releasing hormone and human placental lactogen).
- 1 - Uterine ‘awakening’, initiation of parturition, extending to complete cervical dilatation - increase in gap junction connectivity (prostaglandins), increase in oxytocin receptor numbers (oestrogen) - uterotropins: oestrogen (progesterone, prostaglandins, CRH).
- 2 - Active labour, from complete cervical dilatation to delivery - oxytocin release triggered by the Ferguson Reflex, prostaglandins - Uterotonins: oxytocin and prostaglandins
- 3 - From delivery to the expulsion of the placenta and the final uterine contractions - involution: oxytocin and thrombin.
Cervical Ripening
- Effacement - shortening and thinning of a cervix to get ready for childbirth and allow it to happen.
Positive Feedback Loop of Oxytocin during Labour
Head of baby pushes against cervix > nerve impulses from cervix transmitted to brain > brain stimulates pituitary gland to secrete oxytocin > oxytocin carried in bloodstream to uterus > oxytocin stimulates uterine contractions and pushes baby towards cervix > repeat.
Uterine Contractions
- Prostaglandins
- Oxytocin
- Relaxin
- Stretch Response
Oxytocic Drugs
- Promote uterine contractions
- Induction of augmentation of labour
- Active management of labour
- Treatment of uterine atony and postpartum haemorrhage.
1st Stage of Labour
- Latent phase - under 4cm. ~20hrs. Irregular contractions - every 5-30mins for ~30s.
- Active phase - 4cm-10cm (10cm is full dilatation), rupture of membranes. Regular contractions every 3-5mins which last 1+min (4-6cm) and then progress to intense contractions (6-10cm) which occur every 0.5-2mins and last 60-90 secs. They can overlap. Rupture of membranes e.g. rupture of amniotic sac.