異常分娩專題知識

StagesoflaborThefirststage(theperiodofdilatationandeffacement)istheintervalbetweentheonsetoflabor(fromthebeginingofregularcontracionswhichoccurevery10minutes,fromthemomentofruptureofmembranes)andfullcervicaldilatation(10cm)

-thelatentphasewhichcomprisescervical effacementandearlycervicaldilatation(to3-4cm) -theacceleratedphase(from5to7cm) -thetransitionphase(from8to10cm)StagesoflaborThesecondstage

(theperiodofexpulsion)

lastsfromcompletecervicaldilatationtillthedeliveryoftheinfantThethirdstage

(theplacentalstage)beginsimmediatelyafterdeliveryoftheinfantandendswiththedeliveryoftheplacentaThefourthstageisdefinedastheearlypostpartumperiodofapproximately2hoursafterdeliveryoftheplacenta.DuringthisperiodthepatientundergoessignificantphysiologicadjustmentandmustbeunderclosemedicalcontrolAbnormallabor-dystocia

(difficultlabor)Itresultswhen:-anatomicorfunctionalabnormalitiesofthefetus-abnormalitiesofthematernalbonypelvis-abnormalitiesoftheuterusandcervix-orcombinationoftheseabnormalitiesinterferewiththenormalcourseoflaborAbnormallabordescribescomplicationsofthenormallaborprocess:slowerthannormalprogressoracessationofprogressAbnormallabor(ordystocia)isdividedinto:

-prolongationdisorders

-arrestdisorders

Patternsofabnormallabor-dystocia:

Aprolongedlatentphase

Alatentphaseoflaborisabnormalwhenitlasts

>20hoursinprimigravidpatients

>14hoursinmultigravidpatients

Thecausesofsuchsituation:

-abnormalfetalposition

-?unripecervix”

-administrationofexcessanesthesia

-fetopelvicdisproportion

-disfunctionaluterine

contractions

Aprolngedlatentphasedoesnotitselfposeadangertothemotherorfetus.

Somepatientswhoareinitiallythoughttohaveaprolongedlatentphaseturnoutonlytohavefalselabor.

Patternsofabnormallabor-dystocia:

AprolongedactivephaseAnactivephaseisabnormalwhenitlastslongerthan:-12hintheprimigravidpatients-6hinthemultigravidpatientsorwhentherateofcervicaldilatationislessthan-1,2cm/hinprimigravidpatients-1,5cm/hformultiparasorwhendescendofthepresentingpartislessthan-1,0cm/hforprimigravidas-1,5cm/hformultiparas

Causesofprolongedactivephase:

-abnormalfetalposition

-fetopelvicdisproportion

-excessiveuseofsedation

-inadequatecontractions

-ruptureoffetalmembranesbeforethe onsetofactivelabor

Patternsofabnormallabor-dystocia:

Arrestdisorders:

Secondaryarrestofdilatation:

nocervicaldilatationfor>2hinanycasein theactivephaseoflabor

Arrestofdescend:

nodescentofthepresentingpartin>1hinthesecondstageoflaborItoccurswhen:

-thecontractionsarenolongersufficienttomaintaintheprogressoflabor

or

thelaborarrestsinspiteofadequateuterinecontractionsassociatedwith:

-toolargefetus

-fetallieorpositionthatpreventsprogressinlabor

-toosmallorabnormallyshapedpelvisCorrectdiagnosisandmanagementofabnormallaborrequiresevaluationofthemechanismsoflabor:

-thepower(uterinecontractions)

-thepassenger(fetalfactors-presentation,size)

-thepassage(maternalpelvis)Evaluationofthepowerincludes:

strenght,durationandfrequencyofuterinecontractions-manualpalpationofthematernalabdomenduringacontraction(subjectiveevaluation)-externaltocography(moreobjective)-atocodynamometerisanexternalstraingauge,whichisplacedonthematernalabdomen,itrecordswhentheuterustightnesandrelaxesbutdoesnotdirectlymeasurehowmuchforcetheuterusisgeneratingforagivencontraction-internaltocography(themostobjective)-anintrauterinepressurecatetherisplacedintotheuterinecavityandittransmitstheactualintrauterinepressuretotheexternalstraingauge,whichthenrecordsdurationandfrequencyaswellasthestrengthofthecontractionsForcervicaldilatationtooccur,eachcontractionmustgenerateatleast25mmHgofpressure.Theoptimalintrauterinepressureduringcontractionis50-60mmHg.

Ingeneratinganormallaborpatternthefrequencyofcontractionsisalsoveryimportant.Aminimumthreecontractionsina10minutewindowisusuallyconsideredadequate.Duringthefirststageoflaborarrestoflaborshouldnotbediagnoseduntilthecervixisatleast4cmdilated(beforeendingthelatentphaseoflabor).

Duringthesecondstageoflabor,the?power”includeboth,theuterinecontractileforcesandthevoluntarymaternalexpulsiveefforts(pussing)EvaluationofthepassengerThisincludes:-estimationofthe

expectedfetalweightclinicalevaluationoffetallie,presentation,positionIftheestimatedfetalweightis>4000gtheincidenceofdystocia,includingshoulderdystociaorfetopelvicdisproportionisgreater.CephalopelvicdisproportionisadisparitybetweenthesizeorshapeofthematernalpelvisandthefetalheadIfthefetalheadisextendedalargercephalicdiameter(>32cm)ispresentedtothepelvis,therbyincreasingthepossibilityofdystocia

Abrow

presentation(forehead-thelargestcephalicdiameteris36cm)(1/3000deliveries)typicallyconvertstoeitheravertexorfacepresentation,butifpersistent,causesdystociarequiringcesareansection.

Afacepresentationalsorequirescesareansectioninmostcases,althoughamentumanteriorpresentation(chintowardmother’sabdomen)sometimesmaybedeliveredvaginally.

Persistentocciputposteriorpositionsarealsoassociatedwithlongerlabors(about1hourinmultiparouspatientsand2hoursinnulliparouspatients)

Fetalanomalieslikehydrocephalyandsofttissuetumorsmayalsocausedystocia.Theuseofprenatalultrasoundsignificantlyreducestheincidenceofunexpecteddystociaforthesereasons.EvaluationofthepassageMeasurementsofthebonypelvisarerelativelypoorpredictorsofsuccessfulvaginaldelivery.Itdependsontheinaccuracyofthesemeasurementsaswellascase-by-casedifferencesinfetalaccomodationandmechanismsoflabor.Onlyinrarecases,whenthepelvisis?completelycontracted”(thepelvicdiametersareverysmall)manualevaluationofthediametersofthepelviscanpredictthatthefetuswillnotpassagethebirthcanal.InsomecasestheX-rayorcomputedtomographicpelvimetrycanbehelpful,butthebesttestofpelvicadeqacyistheprogressorlackofprogressofdescendingofthefetalpresentingpartinthebirthcanal.

Exceptthebonypelvis,therearesofttissuescausesofdystocia,suchas:

-distendedbladderorcolon,

-adnexalmass

-uterinefibroidManagementofabnormallaborAugmentationoflaboristhestimulationofuterinecontractionsthatbeganspontaneouslybutareeithertooinfrequentortooweak,orboth.Inductionoflaboristhestimulationofuterinecontractionsbeforethespontaneousonsetoflabor,withthegoalofachievingdelivery.Stimulationorinductionoflaborisusuallycarriedoutwithintravenousoxytocin(sometimesprostaglandines)administratedbymeansofmeteredpump.

Theincidenceofprolongationofthefirststageoflaborcanbeminimizedbyavoidingunnecessaryintervention,i.e:

laborshouldnotbeinducedwhenthecervixisnotwellpreparedorripe(softened,anteriorlyrotated,partiallyeffaced)TheBishopscoreisusedtoquantifythedegreeofcervicalripeningandreadinessforlabor.

Ascoreof0to4pointsisassociatedwiththehighestlikelihoodoffailedinduction.

Ascoreof9to13pointsisassociatedwiththehighestlikelihoodofsuccessfulinduction

InductionoflaborisindicatediftheanticipatedbenefitsofdeliveryexceedtherisksofallowingthepregnancytocontinueIndicationsPost-termpregnancyMaternalmedicalproblemsPregnancy-inducedhypertensionPrematureruptureofmembranesChorioamnionitisContraindicationsPlacentaorvasapreviaCordpresentationAbnormal/unstablefetalliePriortwoormorecesareansectionsPriorclassicaluterineincisionPrioruterineincisionofunknowntypeActivegenitalherpesWhenthecervixisunripe,ProstaglandinE2(Prepidil,Propess)isadministratedintracervicallyortotheposteriorfornixofthevagina.Inthemajorityofthesecaseslaborbeginswithouttheneedofoxytocinstimulation.

Aprolongedlatentphasecanbemanagedbyeitherrestoraugmentationoflaborwithintravenousoxytocinafterexcludingmechanicalfactors.Ifthepatientisallowedtorest,oneoffollowingwilloccur:

-theconractionscanstop,inwhichcasethepatientisnotinlabor(falselabor)

-thecontractionscanbecomemorefrequentandintensive,inwhichcasethepatientwillgointoactivelabor

-thecontractionsmaybeasbefore,inwhichcaseoxytocinemaybeadministratedtoaugmenttheuterinecontractionsTheuseofamniotomy(artificialruptureofmembranes)isalsoadvocatedwithprolongedlatentphase.

Afteramniotomythefetalheadwillprovideabetterdilatingforcethanwouldtheintactbagofwaters.Additionalytheremaybeareleaseofprostaglandines,whichcouldaidinaugmentingtheforceofcontractions.

Theriskofamniotomyis:

-anumbilicalcordprolapse(thepresentingpartshouldbefirmlyappliedtothecervix)

-abruptionoftheplacenta

-intrauterineinfectionIntheactivephaseoflabormechanicalfactorssuchasabnormalpositionorpresentationaswellasfetopelvicdisproportionmustbeconsideredbeforeuseofoxytocin.

Ifthewomanistiredwhichresultsinsecondaryarrestofdilation,restfollowedbyaugmentationwithoxytocinisofteneffective.Artificialruptureofthemembranesisalsorecommended.Risksofprolongedlabor

MaternalFetalinfectionmaternalexhaustionlacerationsuterineruptureuterineatonywithpossiblehemorrhageasphyxiatraumainfectioncerebraldamageProlongedlaborisassociatedwiththepassageofmeconiumintotheamnioticfluidandsubsequentlytheriskofmeconiumaspirationsyndrome(MAS).

Fetuseswhoinhalemeconium-stainedfluidduringlabormaysufferthissyndrom,whichincludesbothmechanicalobstructionandchemicalpneumonitisfromthemeconiummaterial.

Pathologicfactorsinclude:

-atelectasis

-consolidation

-barotrauma

-removalofpulmonarysurfactantbyfreefattyacidsAmniodilutionisamethodofintrapartumtreatmentofmeconium-stainedamnioticfluid.Anormalsalinesolutionisslowlyinfusedthroughatubeinsertedintheuterus,washingmeconium-stainedfluidoutandreplacingitwiththesalinesolution.

Asthefetalheadisdelivered,butbeforedeliveryofthefetalchest,suctioningofthenasopharynxshouldbeperformed.Afterdeliveryofthefetussuctioningoutofmeconiuminthedeeperpartsofrespiratorytract(belowthevocalcords)mustbedone.Techniquesofoperativedeliveryinclude:

-obstetricforceps

-vacuumextraction

-cesareansectionThepurposeoftheforcepsmaneuveristo:1.augmenttheforcesexpellingthefetuswhenthemother’svoluntaryeffortsinconjunctionwithuterinecontractionsareinsufficienttodelivertheinfantandeventuallyto:2.rotatethefetalheadinthebirthcanal,ifitisn’tcompletelyrotatedNecessaryconditionstoapplyforceps:Cervix FullydilatedMembranes RupturedPositionandstation offetalhead KnownandengagedFeto-pelvicdisproportion ExcludedFetus AliveForcepsClassificationOutletforceps-thefetalskullhasreachedtheperinealfloor,thescalpisvisablebetweencontractions,thesagittalsutureisintheanteposteriordiameterLowforceps-theleadingpointoffetalskullis+2stationormoreMidforceps-theheadisengagedbuttheleadingpointoftheskullisabove+2stationHighforceps-theheadishighaboveinletandisn’tengaged,theleadingpointoftheskullabove0(notperformedincurrentobstetrics)ToavoidthepotentialriskoftraumatobothmaternalandfetalpartsapplicationofobstetricforcepsshouldbeperformedbyanexperiencedclinicianBeforeapplicationoftheforcepsthephysicianshouldreassessthefetalposition.

Theneonatologistshouldbenotifiedinadvance,beforeapplicationoftheforceps.

Forcepsshouldbeappliedonlyafterthecervixiscompletelydilatedandifthereisnoevidenceofcephalopelvicdisproportion.

Forcepssshouldbeappliedonly(!!)afterthebiparietaldiameterhaspassedthroughtheinlet,andtheskullhaspassedbelowtheischialspines.

Afterdeliverythegenitaltractandinfantshouldbeexaminedcarefully.

Potentialrisks:

-lacerationsof:thecervix,vagina,perineum,bladderandrectum

-injuriesofthefetus:intracranialhemorrhage,skullfracture,brachialplexusinjury,cephalhematoma,facialparalysis,clavicularfractureVaccumextractionThismaneuverissimilartoforcepsdelivery.Itspurposeistoaugmenttheforcesexpellingthefetuswhenthemother’svoluntaryeffortsinconjunctionwithuterinecontractionsareinsufficienttodelivertheinfant.Advantagesofthevacuumextractorinclude:-lessforceappliedtothefetalhead-reducedanesthesiarequirements-easieraplication-lessperinealtraumatheabilitytopermittheheadtofinditspathoutofthematernalpelvisDisadvantagesofthevacuumextractorinclude:

-theapplicationoftractiononlyduringco