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Ch. 11. Parturition

Ch. 11. Parturition. 부산백병원 산부인과 R1 손영실. # Clinical Course of Labor. INDEX. 1. The Myometrium. 2. The Cervix. 3. Labor Patterns. • Labor : thunderous uterine contractions that effect dilatation of the cervix and force the fetus through the birth canal

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Ch. 11. Parturition

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  1. Ch. 11. Parturition 부산백병원 산부인과 R1 손영실

  2. # Clinical Course of Labor

  3. INDEX 1. The Myometrium 2. The Cervix 3. Labor Patterns

  4. • Labor : thunderous uterine contractions that effect dilatation of the cervix and force the fetus through the birth canal • False labor : myometrial contractions that do not cause cervical dilatation unpredictability in occurrence lack of intensity brevity of duration discomfort – confined to low abdomen & groin

  5. The Myometrium 1. Anatomical and Physiological Considerations • Characteristics – advantage in the efficiency of uterine contractions & the delivery of the fetus ① degree of shortening of smooth muscle cells with contraction : magnitude greater than in striated muscle cells ② forces can be exerted in smooth muscle cells in any direction ③ not organized in the same manner as skeletal muscle - thick & thin filaments in long, random bundles → greater shortening & force-generating capacity ④ multidirectional force generation

  6. Contraction Relaxation Myosin light chain 1) Decreased intracellular Ca2+; Ca2+ sequestration 2) Dephosphorylation of myosin light chain 3) Inactivation of myosin light chain kinase (e.g., by cyclic AMP- dependent phosphorylation) Myosin light chain kinase Ca2+ activated Phosphorylated Myosin light chain Actin Actin-Phosphorylated Myowin ATPase ATP ADP The Myometrium 2. Biochemistry of Smooth Muscle Contractions

  7. The Myometrium 3. The Three Stages of Labor • First stage of labor : begins when uterine contraction of sufficient frequency, intensity & duration are attained → ends when cervix is fully dilatated (10cm) : stage of cervical effacement & dilatation

  8. The Myometrium • Second stage of labor : begins when complete dilatation of cervix → ends with delivery of the fetus : stage of expulsion of the fetus • Third stage of labor : begins after delivery of the fetus → ends with the delivery of the placenta : stage of separation & expulsion of placenta

  9. The Myometrium 4. Clinical Onset of Labor • Show (bloody show) - sign of the impending onset of active labor - extrusion of mucus plug of the cervical canal → discharge of small amount of blood-tinged mucus from vagina

  10. The Myometrium 5. Uterine Contractions Characteristic of Labor ; muscular contractions, those of uterine smooth muscle of labor are painful • cause of pain (not known definitely) ① hypoxia of contracted myometrium ② compression of nerve ganglia in cervix & lower uterus by the tightly interlocking muscle bundles ③ stretching of cervix during dilatation ④ stretching of peritoneum overlying the fundus

  11. The Myometrium • Ferguson reflex : mechanical stretching of cervix enhances uterine activity : manipulation of the cervix and stripping the fetal membranes is associated with an increase in PGF2α metabolite in blood : exact mechanism : not clear • Interval between contractions : 10 minutes at the onset of the first stage → diminishes gradually → 1 minute or less in the second stage

  12. The Myometrium • Periods of relaxation between contractions - essential to welfare of the fetus - unremitting contraction of uterus compromises uteroplacental blood flow, cause fetal hypoxia • Duration of contraction : in active phase Duration 30-90 seconds (average 60 sec) Pressure 20-60 mmHg (average 40 mmHg)

  13. The Myometrium 6. Differentiation of Uterine Activity : During active labor, uterus is transformed into 2 distinct parts (1) Upper segment ① actively contracting ② becomes thicker as labor advances ③ quite firm or hard (2) Lower segment ① relatively passive ② develops into a much thinly walled passage for the fetus ③ much less firm

  14. The Myometrium • Physiologic retraction ring - As a result of the thinning of the lower uterine segment and the concomitant thickening of the upper, the boundary between the two is marked by a ridge on the inner uterine surface • Pathologic retraction ring (the ring of Bandle) - When the thinning of the lower uterine segment is extreme, as in obstructed labor, the ring is very prominent

  15. The Myometrium

  16. The Myometrium 7. Change in Uterine Shape : each contraction produces elongation of uterus with decrease in horizontal diameter → important effect on labor process ① decrease in horizontal diameter → straightening of fetal vertebral column ② lengthening of uterus → longitudinal fibers are drawn taut → pulled upward the lower segment & cervix → important factor in cervical dilatation

  17. The Myometrium 8. Ancillary Forces in Labor : After the cervix is dilated fully, the most important force in the expulsion of the fetus is that produced by increased maternal intrabdominal pressure “Pushing” - increased intrabdominal pressure by contraction of abdominal muscles, simultaneously with forced respiratory efforts with glottis closed - important force in the expulsion of fetus - similar to that involved in defecation

  18. The Cervix 1. Changes Induced in the Cervix with Labor • Effective force of the 1st stage of labor is uterine contraction • As the result of the action of these forces, two fundamental changes take place in the already ripened cervix “effacement & dilatation” • The cervix is said to be completely (fully) dilated : 10 cm

  19. The Cervix 2. Cervical Effacement • obliteration or taking up of the cervix • shortening of the cervical canal (2cm → mere circular orifice with almost paper thin edge) • muscular fibers at about the level of the internal os are pulled upward or “taken up” into the lower uterine segment • external os remains temporarily unchanged

  20. The Cervix

  21. The Cervix

  22. The Cervix 3. Cervical Dilatation : as the uterine contraction cause pressure on the membranes → the hydrostatic action of the amnionic sac in turn dilates the cervical canal

  23. Labor Patterns 1. Pattern of Cervical Dilatation • Friedman “Except for cervical dilatation & fetal descent, none of the clinical features of parturient appears to be useful in assessing labor progression” • pattern of cervical dilatation during normal labor course : sigmoid curve

  24. Labor Patterns - 2 phases of cervical dilatation (1) Latent phase : more variable : subject to sensitive changes by extraneous factors and by sedation (prolongation) and myometrial stimulation (shortening) (2) Active phase ① Acceleration phase usually predictive of the outcome of a particular labor ② Phase of maximum slope good measure of the overall efficiency of the machine ③ Deceleration phase more reflective fetopelvic relationship

  25. Labor Patterns - 2nd stage of labor commences after complete cervical dilatation→ only progressive descent of fetal presenting part is available to assess the progress of labor

  26. Labor Patterns 2. Pattern of Descent - In many nulliparas, ① engagement is accomplished before labor begins ② further descent does not occur until late in labor ③ increased rates of descent are ordinarily observed during the phase of maximum slope

  27. Labor Patterns 3. Criteria of Normal Labor • Friedman : Concept of 3 functional divisions of labor ① Preparatory division - latent & acceleration phases - sensitive to sedation & conduction analgesia - little cervical dilatation occurs, considerable changes take place in the extracellular matrix of cervix (collagen & other connective tissue component)

  28. Labor Patterns ② Dilatational division - phase of maximum slope of cervical dilatation - most rapid rate of dilatation occur - unaffected by sedation or conduction analgesia ③ Pelvic division - deceleration phase & second stage - involve the cardinal movement of the fetus

  29. Labor Patterns 4. Rupture of the Fetal Membranes - spontaneous rupture of membrane most often(+) sometime during the course of active labor - premature rupture of the membrane : rupture of membranes before the onset of labor at any stage of gestation

  30. Labor Patterns 5. Placental Separation “3rd stage of labor” • begins immediately after delivery of the fetus, involve the separation & expulsion of the placenta • after delivery of placenta & fetal membranes, active labor is completed • occurs within a very few minutes after delivery

  31. Labor Patterns 6. Separation of Amniochorion : great decrease in the surface area of uterine cavity → fetal membranes (amniochorion) & parietal decidua to be thrown into innumerable folds → increase thickness of the layer from less than 1 mm to 3-4 mm : membranes usually remain in situ until placental separation is nearly completed

  32. Labor Patterns 7. Placental Extrusion : women in recumbent position frequently cannot expel placenta spontaneously → artificial means of completing the 3rd stage is generally required → compress & elevate fundus while exerting minimal traction on umbilical cord

  33. Labor Patterns 8. Mechanisms of Placental Extrusion (1) Schultze mechanism • placental separation occurs first at central areas → retroplacental hematoma → push the placenta toward uterine cavity (2) Duncan mechanism ① placental separation occurs first at the periphery ② blood collects between the membranes & uterine wall → escapes from the vagina

  34. 감사합니다.

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