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Physiology & mechanism of parturition (Cardinal movement of Vertex…
Physiology & mechanism of parturition
Mechanisms
:fireworks:
4 phases
Quiescence
- Uterine quiescence & cervical softening
นิ่งสงบ
No. of
beta-agonist
receptors increasing ➨ no UCs
*any stimulation of receptor in this phase ➨ Abortion
:red_flag:
Abn
. in this phase:
Abortion, Preterm labor, Incompetence
Cervix
Timing
: since preg till 32 - 34 wks
:small_red_triangle:
changes
:
Uterine quiescence
Unresponsive to natural stimuli
Contractile paralysis
Size and Vascularity changes softening
Some myometrial contractions occur
not cause Cx dilatation
Braxton-Hicks contraction / False labor pain
:baby:
Cervical change
Maintenance of
barrier func
to protect reproductive tract fr infection
Maintenance of
cervical competence
despite inc gravitational forces
Cervical
softening
Activation
- Preparation for labor
Timing
: 32 - 34 wks (last 6-8 wk of preg) till
:red_flag:
Abnormal
in this phase:
Abortion, Premature labour
:small_red_triangle:
changes
:
Progressive change of
uterus
:arrow_up: Uterine
irritability
&
responsiveness
to uterotonins
Formation of LUS (lower uterine segment) from the isthmus
Cervical
ripening
Connective tissue changes
Weeks or Days before onset of contractions
Ratio changes
:
Hyaluronon :arrow_up: ➭ อมน้ำมากขึ้น
Dermatan sulfate :arrow_down: ➭ Cx softening
Stimulation
- Process of labor
:green_apple:
True labor pain
(3 stages) ➨ 1st stage of labor ➨ 2nd stage of labor ➨ 3rd stage of labor
:small_red_triangle:
changes
:
Ferguson reflex
(
self-staining cycle of UC
)
Uterotonin
➭ regulates UC & Cx dilatation
Uterine labor contraction
due to
Compression of nerve ganglia
Stretching of myometrium
Hypoxia of myometrium
Cx stretch
Cx effacement & dilatation
Pelvic floor changes
:red_flag:
Abn
. in this phase:
Post date
or
Post term pregnancy
(As oxytocin receptors increase slightly as we dunno
when CAH is created) ➨ :watermelon:
Rx
: gives PGs, Oxytocin to induce labor
Timing
:
Involution
- Parturient recovery
:glass_of_milk: Good breastfeeding should be ≥ 6 months (
shouldn't > 2 yrs
)
Timing
: Immediate after delivery till End of puerperium (6 weeks)
:<3:
Physiological
& :male-scientist::skin-tone-4:
Biochemical
process regulating paturition
phase 1
Quiescence
(result of many factors that include:)
Estrogen & Progesterone actions via Intracellular receptors
Myometrial cell plasma membrane receptor mediated
Beta-adrenergic receptor (myometrial relaxation)
LH/hCG receptor (Uterine quiescence)
Relaxin
Corticotropin releasing hormone
Prostaglandins: PGE2 & PGI2
Generate cGMP ➭ Atrial & Brain Natriuretic Peptides (ANP & BNP)
Modification of myometrial-cell ion channels
phase 2
Activation
Functional
Progesterone
withdrawal
:arrow_up: oxytocin receptor
Relaxin
Remodeling of ECM of uterus
Cx softens
Vx relaxation
Lengthen pubic symphysis ligament
Promote cell proliferation
Inhibiting apoptosis
Fetal contribution to initiate parturition
Uterine stretch
Corticotropin releasing hormone (placenta & hypothalamus)
Fetal lung surfactant (Surfactant protein A aka SP-A): SP-A activates myometrial contraction
Figures :grapes:
phase 3
Stimulation
phase 4
Involution
:crossed_swords:
Stages of labor
1st stage
: True labor pain - Cx fully dilated
True/False labour
Friedman's curve
Latent phase
Active phase
Acceleration
Maximum slope
Deceleration
2nd stage
: Cx fully dilated - Fetus delivery
3rd stage
: Fetus delivery - Delivery of placenta and membrane
3 signs
:red_circle:
Uterine
sign (shape of uterus from discoid ➭ globular)
:red_circle:
Vulvar
sign (Vx bleeding)
:red_circle:
Cord
sign (สายสะดือเคลื่อนต่ำ ไม่มีกลับช่องคลอด)
:alarm_clock: duration for
Nulliparous
1st stage (
12 hrs
) ➭ 2nd stage (
50-60 mins
) ➭ 3rd stage (~
5 min
)
Multiparous
1st stage (
8 hrs
) ➭ 2nd stage (
20-30 mins
) ➭ 3rd stage(
~5 mins
)
Estimated blood loss ~ 300 - 500 mL
Factors affecting labor (
3Ps
) :dango:
Power
:male-firefighter:Uterine contraction (
optimum= interval 2-3 mins, duration 45-60 sec, severity 2+)
:male-firefighter: Pushing
*Cx fully dilated แล้วเราเสริมให้เบ่ง
I/C การเบ่ง =
UCs
เบ่ง 3 ครั้ง / UC 1 ครั้ง
Passage
:railway_track:Cervix by PV
:railway_track:Pelvis by Clinical pevimetry
Pelvic
inlet
: Obstretic conjugate > 10 cm, Diagonal conjugate > 11.5 cm
Mid
pelvis: Interspinous diameter > 10 cm
Pelvic
outlet
: Intertuberous diameter > 10 cm, Suprapubic angle > 85 deg
Passenger
Attitude
Fetal axis/Lie
Presentation
Position (reference point)
Station
Cardinal movement of Vertex presentation
(
LOA
)
Engagement
Descent
Flexion
Internal rotation
Extension
Restitution & External rotation
Expulsion
Mechanism of labor
Engagement
PE by
Pawlik’s grip
Bilateral inguinal grip
PV: station 0
Abn
Asynclitism
Molding
Caput succedaneum
Flexion
Descent
Internal rotation
Extension
Restitution and external rotation
Expulsion