MECHANISM OF LABOUR- OBSTETRICS AND GYNAECOLOGY

ASSOCIATE PROFESSOR

1. UNIT -4
MECHANISM OF LABOUR

2. Definition-Labour
Labourmaydefinedasrhythmiccontractionand
relaxationoftheuterinemuscleswith
progressiveeffacementanddilatationofthe
cervix,leadingtoexpulsionoftheproductsof
conception.

3. Definition: Mechanism of Labour
LABOUR-1.Aseriesofpassive,adaptivemovements
ofthefetalheadandshoulderssmallestdiameterto
passthroughthebirthcanal.
2.Themechanismoflabourarethepositional
movementsthatthefetusundergoesto
accommodateitselftothematernalpelvis.

4. Terminology :
1.Lie: the relation of the long axis of the fetus to that of
the mother
Eg.
. longitudinal lie
.transverse lie
2.Attitude: posture of the fetus
Head flexed over the chest
Arms/hands flexed over the chest
Thighs/legs flexed over the abdomen
3.Presentation: the presenting part is the portion of the
body of the fetus
EG: vertex presentation, brow presentation, face
presentation.

5. 4.Position : the relation of an arbitrary chosen point
of the fetal presenting part to the right or left side of
the maternal birth canal.
EG. LOA-LEFT OCCIPITO ANTERIOR
ROA-RIGHT OCCIPITO ANTERIOR

6. Cardinal movements of labour
1.Engagement
2. Descent
3.Flexion
4.Internal rotation of the head
5.Crowning
6.Extension
7.Restitution
8.External rotation of the head / internal rotation of
shoulder
9.Lateral flexion of the body and shoulder through
birth canal.

7. ENGAGEMENT
Engagementtakesplacewhenthebipareital
diameterofthefetalheadhaspassedthrough
thepelvicinlet.
Inprimigravida,itusuallyoccurs12hours.Inmulti
itwilloccurwithin6hrs.

8. DESCENT
Itisacontinuousmovementthroughoutthe
processofdelivery.Descentresultinnumber
offorcesincludingcontractions,andmaternal
pushingeffortwithcontractionofher
abdominalmuscles.

9. FLEXION
Astheheaddescends,itmeetsresistancefromthe
pelvicwallsandfloorandthisleadstoincreasedflexion
ofthehead.
Astheheadflexeditbringstheshortestlongitudinal
diametreofthehead(sub–occipito–bregmatic9.5cm)
topassthroughthebirthcanal.

10. Internal rotation of the head
Theocciputleadsandmeetsthe
pelvicfloorfirstandrotates
anteriorly1/8ofacircle.

11. Afterinternalrotationofhead,furtherdescentoccursuntilthe
occiputliesunderneaththepelvicarch.Atthisstage,the
maximumdiametreofthehead(biparietaldiametre)
stretchesthevulvaloutlet.
CROWNING

12. EXTENSION
Oncecrowninghasoccurred,thefetalhead
ispivotunderthesymphysispubisandthe
sinciput,faceandchinsweepoverthe
perinium.

13. RESTITUTION
withrestitution,theocciput
moves1/8ofacircletowardsthe
sidefromwhichitstarted.

14. Internal rotation of
shoulder
Theanteriorshoulderreachesthepelvic
floorandrotatesanteriorly1/8thofacircle.
Theshouldercometolieintheanterio
posteriodiametreofthepelvicoutlet.

15. EXTERNAL ROTATION OF HEAD
Theheadrotates1/8thofacircle
towardsthesymphysispubisfromthe
obliquediameter.

16. LATERAL FLEXION OF BODY AND
HEAD
Aftertheshoulderaredelivered,the
bodyisbornbylateralflexionflowing
thecurveofcarns.

17. Thank
you