8 ( Has no obstetrical significance , it is not considered further) PLANES AND DIAMETER OF THE PELVISHAVING 4 IMAGINARY PLANES :1. The plane of the pelvic inlet ( Superior strait )2. The plane of the pelvic outlet ( Inferior strait )3. The plane of the mid pelvis ( least pelvic dimensions )4. The plane of greatest pelvic dimensions( Has no obstetrical significance , it is not considered further)
15 GYNECOID PELVIS ANDROID PELVIS - Almost 50% of white women (Todd’ Collection study)- Ascertained the frequency of the four parent pelvic typesby study of Todd’s Collection ( Caldwell & CoWorkers,1939)ANDROID PELVIS- 1/3 of pure type pelvis ( white women), 1/6 non white women- The extreme android pelvis presages poor prognosis for vaginaldelivery- The frequency of difficult forceps operations increases
16 INTERMEDIATE TYPE PELVIS ANTHROPOID PELVIS- 1/4 pure type pelvis in white women and nearly1 1/2 of those in non white womenPLATYPELLOID PELVIS- Rarest of the pure varieties ( < 3% )INTERMEDIATE TYPE PELVIS- Mixed type- More frequent than pure types
18 PELVIC SIZE AND ITS CLINICAL ESTIMATION - Pelvic inlet measurements- Diagonal conjugate- Engagerment : - with engagerment, the fetal headserves as an internal pelvimeter to demonstratethat the pelvic inlet is ample for that fetus.
19 PELVIC INLET- Obstetrical conjugate ( normal > 10 cm)- Diagonal conjugateCD to 2 cm = True conjugate
26 PELVIC OUTLET MEASUREMENTS ( diameter between the ischial tuberosities )Called as :- Biischial diameter , Inter tuberous diameter, Transversediameter of the outlet- The shape of the sub pubic arch also can be evaluatedat the same time by palpating the pubic rami from thesub pubic region toward the ischial tuberosities.- Estimated by placing a closed fist against theperineum between the ischial tuberosities, after fistmeasuring the width of the closed fist ( usually > 8 cm )
27 MID PELVIS ESTIMATION- Clinical estimation of mid pelvis capacity by any direct form of measurement is not possible -Suspicion contracted pelvis in this region :- Ischial spines are quite prominent- The side walls are felt to converge- The concavity of the sacrum is very shallow- Ischial diameter of the outlet < 8 cm
30 95 % of all labors is in vertex presentation and most commonly ascertained by abdominal palpation and confirmed by vaginal examinationMajority of cases the vertex enters the pelvis with the sagittal suture in the transverse pelvic diameterThe fetus enters the pelvis in the Left Occiput Transverse Position / LOT (40% of labors) & 20% ROT.The head either enters the pelvis with the occiput rotated 45o anteriorly from the transverse position
31 20 % of all labors the fetus enters the pelvis in an Occiput Posterior (OP) position. The ROP is slightly more common than LOP and posterior positions are more often associated with a narrow forepelvisThe head either enters the pelvis with the occiput rotated 45o anteriorly from the transverse position
32 THE CARDINAL MOVEMENTS OF LABOR ARE : ENGAGEMENTDESCENTFLEXIONINTERNAL ROTATIONEXTENSIONEXTERNAL ROTATIONEXPULSION
33 ENGAGEMENTThe biparietal diameter, the greatest transverse diameter of the fetal head in occiput presentations, passes through the pelvic inlet is designated engagement (during the last few weeks of pregnancy)A normal – sized head usually does not engage with its sagittal suture directed anteroposteriorly.Instead, the fetal head usually enters the pelvic inlet either in the transverse diameter or in one of the oblique diameters.
34 ASYNCLITISMAlthough the fetal heads tends to accommodate to the transverse axis of the pelvic inlet, the sagittal suture , while remaining parallel to that axis, may not lie exactly midway between the symphysis and sacral promontoryThe sagittal suture frequently is deflected either posteriorly toward the promontory or anteriorly toward the symphysis.Such lateral deflection of the head to a more anterior or posterior position in the pelvis is called asynclitismModerate degrees of asynclitism are the rule in normal labor, but if severe , may lead to CPD
35 DESCENTIn nulliparas, engagement may take place before the onset of labor and further descent may not follow until the onset of second stage. In multiparous women, descent usually begins with engagement.Descent is brought about by one or more of four forces :Pressure of the amniotic fluidDirect pressure of the fundus upon the breech withcontractionsBearing down efforts with the abdominal musclesExtensions and straightening of the fetal body
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