Stages of parturition

• Parturition

  • Expulsion of foetus and placenta
  • Subdivided into 3 stages
• Parturition - Stage 1

  1. Initiation of myometrial contractions

  2. Removal of progesterone block

  3. Foetal cortisol promotes the synthesis of three enzymes that convert progesterone into estradiol; also causes the placenta to synthesize PGF2α

  4. Cervical relaxation and dilation

  5. Removal of cervical seal

  6. Vaginal and vulvar relaxation

  7. Foetal position/orientation
• Parturition - Stage 2

  1. Relaxin (produced by either the CL or the placenta, depending upon the species) is stimulated by PGF2α → causes a softening of the connective tissue in the cervix, promotes elasticity of the pelvic ligaments, prepares the birth canal by loosening the supportive tissues so that passage of the foetus can occur with relative ease

  2. Cervix completely dilated

  3. Delivery of foetus via intense, coordinated uterine and abdominal contractions
• Parturition - Stage 3

  1. Expulsion of the foetal membranes quickly follows expulsion of the foetus

  2. The chorionic villi become dislodged from the crypts of the maternal side of the placenta
• Maternal hormones involved in parturition

  • Progesterone
  • Estrogen
  • Prostaglandin
  • Oxytocin
  • Relaxin