Parturition - Erez

Question 1

What are the 4 phases of labor?

Answer 1

Phase 0: Quiescence

Phase 1: Activation

Phase 2: Stimulation

(Parturition)

Phase 3: Involution

Question 2

What hormones are relevant in quiescence (phase 0)?

Answer 2

Estrogen:
decreases prostaglandins, inflammatory cells in cervix and gap junctions

Other inhibitors:
Progesterone (released by cholesterol, inhibits expulsion)
Prostacyclin
Relaxin
Nitric oxide
PTH-related peptide: CRH (corticotropin-releasing hormone, human placental lactogen)

Fetal membranes releases cortisol –> maternal hypothalamus –> maternal oxytocin release, cortisol negative feedback on hypothalamus

Ratio of progesterone/estrogen high

Question 3

Which hormones are relevant to phase 1, activation?

Answer 3

Uterotropins:
Estrogen
Inhibition of proggesterone, prostaglandins
Activation of CRH

Question 4

Which hormones are relevant during phase 2, stimulation?

Answer 4

Uterotonins:
Prostaglandins
-placental clock, induce labor
-myometrial contractility, cervical ripening, extracellular matrix degradation, induce abortion/labor, induce gap junction formation (required but not sufficient for communication and synchronization of labor, connexin 43 increases in labor)
-Inhibitors delay abortion/labor
Oxytocin

Then the active phase of labor ends with delivery of fetus and placenta

Fetus releases CRH –> pituitary ACTH –> cortisol release –> fetal prostaglandins

Ratio of progesterone to estrogen decreases- prog is more local

Question 5

What hormones are relevant to phase 3, involution?

Answer 5

Oxytocin, thrombins

Uterus shrinks back close to original size and ready for another labor

Question 6

What are the components of the common pathways of parturition?

Answer 6

1. Activation and contraction of the myometrium
2. Dilatation (up to 10cm) and effacement of cervix: gets paper thin and water enters

After full dilatation:

3. Decidua activation and dissolution of membranes

Question 7

What is the time of gestation on average?

What is considered postterm and preterm delivery?

Answer 7

Term delivery- between 37-42 weeks of gestation from last menstrual period
• Post term delivery – after 42 weeks of gestation
• Preterm delivery – before 37 weeks of gestation

Question 8

How do PGE2 and PGF2alpha affect the 2 amniotic fluid compartments

Answer 8

PGE2 more prominent in the upper compartment but then decreases and PGF2a increases and surpasses it later in labor indicating a stronger uterotonic effect of PGF2a over E2.

Similar pattern in the forebag with PGE2 overall more but then PGF2a overtaking PGE2.

Higher levels overall in the forebag of both over the upper compartment.

Question 9

How are oxytocin receptors distributed across the uterus?

Answer 9

Higher number of receptors in the fundus and upper 2/3

In lower uterus there are fewer receptors because there is more connective tissue and less muscle

During dysfunctional labor a contraction will pass through and “get stuck” with the baby in the more fibrotic part of the uterus and doesn’t go all the way down –> hourglass

Women have nightly bursts of contraction