Partuition and Labor

Question 1

Phase 0 (myometrium and cervix)

Answer 1

• Uterine Quiescence (conception - 35 or 36 wks)
• Myometrial hyperplasia and hypertrophy
• Myometrium is unresponsive (limited uterotonins like PGs and oxytocin, limited propagation of contraction signals)
• Myometrium is relaxed b/c low intracellular Ca++ (electronegative cell)
• Cervix is rigid and non-distensible - acts as structural and immune barrier (organized collagen bundles)

Question 2

What is the main hormone involved in Phase 0?

Answer 2

Progesterone

Question 3

Phase 1 (myometrium and cervix)

Answer 3

• Myometrial Activation (2-6 wks - prep for labor)
• Inc spontaneous contractions (inc # gap junctions - connexin 43)
• Inc response to uterotonins (inc # uterotonin receptors on myometrium)
• Cervix ripens (collagen breakdown and more glycosaminoglycans which pull water into cervix; inc compliance)

Question 4

What hormones are involved in phase 1?

Answer 4

• Estrogen (from fetus - DHEA as fetal HPA axis matures –> converted to estrogen)
• Estrogen is responsible for gap junctions, Ca channels, oxy receptors, COX2 for PGS, new progesterone receptor isoform
• No fall in progesterone BUT shift in progesterone receptor expression; express PR-A at tissues which is an antagonist (“functional withdrawal”)
• CRH
• Placental CRH inc w/ GCs, stress and inflammation - pos feedback
  
  • Also dec CRH binding protein so inc in free CRH
  • More CRH –> more DHEA and more cortisol (important for fetal organ development including lungs)
• CRH / Cortisol also inc prostaglandin synthesis

Question 5

Phase 2 (myometrium and cervix)

Answer 5

• Myometrial Stimulation (<24 hrs - labor & delivery)
• Inc uterotonins and uterotonin receptors, inc gap junctions, contractility
• Contraction
• Profound inflammatory response of proteases and leuks –> cervix effacement/thinning

Question 6

What hormones are involved in phase 2?

Answer 6

• Initiated by prostaglandins (made locally - autocrine / paracrine from amnion and chorion)
• Maintained by oxytocin (not inc in production / serum concentration but inc expression of oxy receptors at myometrium)

Question 7

How are contractions stimulated?

Answer 7

• Oxy, PGE2, PGF2alpha –> bind receptors –> PLC –> IP3 and DAG
• IP3 –> release of Ca from SR –> contraction
• DAG –> protein kinase C –> AA –> more prostaglandins
• Contraction when inc intracellular Ca –> binds calmodulin –> act myosin light chain kinase –> phosphorylates myosin light chain –> binds actin

Question 8

Phase 3

Answer 8

• Involution (4-6 wks - uterine involution, lactation starts, infertile)
• Oxytocin leads to …
  - Placenta expulsion
  - Uterine involution (to prevent hemorrhage)
  - Milk letdown
• Return of fertility dep on duration of breastfeeding
  - 4-8 wks if do not breastfeed
  - Months to a yr if cont to breastfeed

Question 9

What drugs prevent and induce contractions?

Answer 9

• Prevent - beta agonists (not used anymore) and Ca channel blockers or COX inhibitors (dec prostaglandins)
• Induce - prostaglandins and oxytocin

Question 10

Labor Stage 1

Answer 10

• Contractions associated w/ cervical changes
• 1- Early Latent Phase - regular contractions; soften cervix to 4-5 cm
• 2- Active Phase - stronger contractions; rapid cervical dilation (more steep slope in cervical dilation); descent of fetal head
• Ends when dilated to 10 cm (amount needed to pass fetus)
• Timing: variable, few hrs to > 24 hrs

Question 11

Labor Stage 2

Answer 11

• From complete cervical dilation to delivery
• Valsalva / pushing coordinated w/ natural uterine contractions
• Timing: < 3 hrs

Question 12

Labor Stage 3

Answer 12

• Delivery of fetus; then delivery of placenta and fetal membranes
• Timing: < 30 min

Question 13

7 Steps of Fetal Movement in Labor

Answer 13

• 1- Engagement
• 2- Descent
• 3- Flexion
• 4- Internal Rotation
• 5- Extension
• 6- Restitution and External Rotation
• 7- Expulsion