Varney's Ch 25 A&P during Labor and Birth Flashcards
What are the three P’s of labor?
Power (uterus), passenger (fetus), and passage (pelvis)
Onset of labor
occurrence of regular painful contractions that dilate the cervix. *Cervical change is the true sign of labor
Prelabor signs
Fetal engagement (dropping)
Cervical change (increased discharge, mucous plug, vaginal spotting)
What are the four phases of cervical remodeling?
- softening - throughout pregnancy
- ripening - before and during first hours of labor
- dilation - opening/widening of cervix
- repair
Physiologic change during cervical ripening
increased hydrophilic non-collagenous proteins causing the collagen in the cervix to become soluble and disorganized. Then more with inflammatory process by macrophages cytokines and prostaglandins which weaken cervical connective tissue.
What are the phases of the first stage of labor?
Stage 1 - latent
Stage 2 - Active
Stage 3 - Transition
What is second stage of labor
complete dilation, pushing, and birth
what is third stage of labor
time from birth to placenta
what is fourth stage of labor
first hour after birth
What is the placental-fetal-decidual clock theory? “Placental clock”
CRH (corticotropin-releasing hormone) increases during pregnancy and peaks at birth. CRH help initiate labor with a shift in the receptors in the myometrium to promotion of contractility. CRH enhances uterine response to oxytocin and prostaglandins. CRH stimulates the fetal HPA axis to produce cortisol-stimulating more CRH-causing positive feedback loop-stimulating labor and contractions.
What is the progesterone withdrawal theory?
1) During pregnancy-progesterone binds to PR-B (progesterone receptor B) = suppression of contractile protein formation, prostaglandin and oxytocin receptors.
2) During labor- myometrium expresses more PR-A than PR-B, which promotes pro-inflammatory effects=increasing concentration of PR-A resulting in functional progesterone withdrawal without altering concentrations
Inflammation theory of labor initiation
- Inflammation markers increase 2-4 weeks prior to labor
- Uterine stretching causes myometrial cells to trigger inflammatory response (twins have earlier onset of labor)
- cytokines promote Ca for uterine contractions
- Placental aging cells release inflammatory response.
4 phases of partuition
- Phase 1 -Quiescence=inhibits uterine activity (progesterone, relaxin, nitric oxide)
- Phase 2 -Activation=prepares uterus (oxytocin and prostaglandin receptors increase)
- Phase 3 -Stimulation=uterine contractions (oxytocin, prostaglandin)
- Phase 4 -Involution= (oxytocin)
Where is oxytocin produced and where is it excreted?
produced= hypothalamus (also some in decidua and fetal membranes)
excreted=posterior pituitary
How does prostaglandin effect oxytocin receptors?
upregulation, and once bound promotes more prostaglandin production.
How much do oxytocin receptors increase during birth?
200 times compared to prelabor.
Can oxytocin receptors become desensitized to oxytocin?
yes. from prolonged exposure to oxytocin causing a downregulation of receptors, reducing calcium release, impairing labor progress, uterine atony postpartum.
What is the “physiologic retraction ring” called that can be seen between the two uterine segments?
Bandl’s ring
What is the term for the propagation of the contraction wave?
“Triple descending gradient” of fundal dominance.
1) ctxn starts in the fundus
2) lasts longer in the fundus
3) progresses from fundus to isthmus
What are the cardiovascular changes in labor and birth?
1) Cardiac output increases 10-15% in first stage and 50% in second stage from increases stroke volume
2) increased BP during ctxns, return to baseline in-between
How much volume of blood flows through the uterus each minute at term?
5000-900 mL
What happens to placental blood flow during a contraction?
Blood flow is reduced during a contraction (300-500 mL blood flows back to mother during ctxn). Circulation is restored when uterus relaxes.
What hematologic changes happen in labor?
1) Clotting factors VII increase
2) WBCs increase up to 20
What respiratory changes occur in labor?
Increase O2 demand
Reduced total lung capacity
Increased pain can increase RR
