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MECHANISM OF LABOUR

MECHANISM OF LABOUR. Lateefa Al Dakhyel FRCSC, FACOG Assistant professor & consultant Obstetric & gynecology department Collage of medicine King Saud University. Lie, presentation, attitude, &position. FETAL LIE The relation of the long axis of the fetus to that of the mother

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MECHANISM OF LABOUR

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  1. MECHANISM OF LABOUR Lateefa Al Dakhyel FRCSC, FACOG Assistant professor & consultant Obstetric & gynecology department Collage of medicine King Saud University

  2. Lie, presentation, attitude, &position FETAL LIE • The relation of the long axis of the fetus to that of the mother 1-Longitudinallie -99% of labors at term 2-transverselie  multiparty, placenta previa, hydramnious, & uterine anomalies 3-obliquelie -maternal & fetal axes cross @ 45 angle -most unstable & become longitudinal Or transverse at labor.

  3. ATTITUDE or posture. In later months posture of the fetus folded on itself to accommodate the shape of the uterus (flexed head, thighs, knees &feet ,the arms crossed over the chest) Change from this flexed attitude can cause abnormal presentations

  4. (A) vertex (B) sinciput (C) brow (D) face

  5. Fetal position The relation of a chosen point of the fetal presenting part to the Rt or Lt side of the maternal birth canal The chosen point • Vertex presentation  occiput • Face presentation  mentum • Breech presentation Sacrum Each presentation has two positions Rt or Lt Each position has 3 varieties : Ant, transverse, post OA ROA LOA ROT LOT ROP LOP OP

  6. Lie, presentation, attitude, &position CEPHALIC PRESENTATION • Head is flexed sharply  vertex / occiput presentation • Head is extended sharply  face presentation • Partially flexed  bregma presenting (sinciput presentation) • Partially extended  brow presentation BREECH PRESENTATION • Frank breech • Complete breech • Footling breech (incomplete breech) .

  7. FREQUENCY OF VARIOUS PRESENTATIONS & POSITIONS AT TERM • Vertex  96% 2/3 Lt 1/3 Rt • Breech  3.5% • Face 0.3% • Shoulder0.4%

  8. MECHANISM OF LABOUR WITH OCCIPUT PRESENTATIONSTHE CARDINAL MOVEMENTS OF LABOUR 1-ENGAGEMENT The greatest transverse diameter BPD passes through the pelvic inlet It may occur in the last few weeks of pregnancy or only in labour especially in multipara The fetus enters the pelvis in transverse or oblique diameter • LOT  40% • ROT 20% • OP 20% ROP >LOP • ROA / LOA20%

  9. THE CARDINAL MOVEMENTS OF LABOUR 2-DESCENT • In nullipara engagement takes place before the onset of labour & further descent may not occur till the 2nd stage • In multipara descent begins with engagement • It is gradually progressive till the fetus is delivered • It is affected by the uterine contractions & thinning of the lower segment

  10. 3-flexion • The descending head meets resistance of pelvic floor, Cx & walls of the pelvis   flexion • The shorter suboccipito-begmatic is substituted for the longer occipito-frontal

  11. 4-INTERNAL ROTATION • Turning of the head from the OT position  anteriorly towards the symphysis pubis ie. Occiput moves from transverse to ant 45º • Less commonly OT  posteriorly towards the sacrum 135º • It is not accomplished till the head has reached the spines The levator ani muscles form a V shaped sling that tend to rotate the vertex anteriorly

  12. 5-EXTENSION • When the flexed head reaches the vulva it undergoes extension  the base of the occiput will be in direct contact with the inferior margin of the symphysis pubis • Crowning  the largest diameter of the fetal head is encircled by the vulvar ring • The head is born by further extension as the occiput, bregma (ant.fontanelle), forehead, nose, mouth & chin pass successively over the perineum

  13. 6-EXTERNAL ROTATIONRESTITUTION • After delivery of the head it returns to the position it occupied at engagement , the natural position relative to the shoulders (oblique position)Restitution • Then the fetal body will rotate to bring one shoulder anterior behind the symphysis pubis ( biacromial diameter into the APD of the pelvic outlet) • Restitution is followed by complete external rotation to transverse position (occiput lies to next to Lt maternal thigh) • The ant shoulder slips under the pubis • By lateral flexion of the fetal body the post shoulder will be delivered & the rest of the body will follow

  14. OCCIPUT POSTERIOR POSITION • Mechanism of labour is identical to OT & anterior varieties • Usually more longer. • The occiput rotate to the symphysis pubis through 135º instead of 90º or 45º • If rotation does not occur direct occiput post (5-10%)or Partial rotation transverse arrest

  15. Q.1-Commonest presentation during labor is 1-left occiput anterior position (LOA) 2-right occiput anterior (ROA) 3-occiput transverse (OT) 4-left occiput posterior (LOP) • Q.2- about breach presentation which is correct 1-beech presentation is the more common in primeparous 2-incomlete breach can’t be delivered vaginally 3-breach presentation can’t be diagnosed clinically 4-all breach presentation should be delivered by C/S • Q.3-during labor 1-engagment occur when BPD reach the pelvic outlet 2-engagment always occur before onset of labor in prime. 3-if internal rotation to SP is 135 degree it will be OP 4-if the head is flexed it will be face presentation

  16. Thank you

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