Labor and Birth Processes. Clinical Management
KEY TERMS AND DEFINITIONS asynclit asyn clitism ism Oblique presentation of the fetal head at the superior strait of the pelvis the pelvi! planes and those of the fetal head are not parallel attitude atti tude Relation of fetal parts to ea!h other in the uterus "e#$#% all parts fle&ed% or all parts fle&ed e&!ept ne!' is e&tended( biparietal diameter )ar$est transverse dia*eter of the fetal head e&tends fro* one parietal bone to the other bloody sho+ ,a$inal dis!har$e that ori$inates in the !ervi& and !onsists of blood and *u!us in!reases as !ervi& dilates durin$ labor dilation Stret!h Stret!hin$ in$ of the e&tern e&ternal al os fro* an openin$ a fe+ *illi* *illi*eters eters in si-e to an openin$ lar$e enou$h to allo+ the passa$e of the fetus effacement Thinnin$ and shortenin$ or obliteration of the !ervi& that o!!urs durin$ late pre$nan!. or labor or both engagement In obstetri!s% the entran!e of the fetal presentin$ part into the superior pelvi! strait and the be$innin$ of the des!ent throu$h the pelvi! !anal Refle& le& !on !ontra! tra!tio tions ns "ur "ur$e $e to pus push( h( of the ute uterus rus afte after r Fergus Fer guson on re refle flex x Ref sti*ulation of the !ervi& font fo ntan anel elss /r /roa oad d ar area eas% s% or so soft ft sp spot ots% s% !o !ons nsis isti tin$ n$ of a st stro ron$ n$ ba band nd of !onne!tive tissue !onti$uous +ith !ranial bones and lo!ated at the 0un!tions of the bones lie Relationship e&istin$ bet+een the lon$ a&is of the fetus and the lon$ a&is of the *other in a lon$itudinal lie% the fetus is l.in$ len$th+ise or verti!all.% +hereas in a transverse lie% the fetus is l.in$ !ross+ise or hori-ontall. in the uterus lightening Sensation of de!reased abdo*inal distention produ!ed b. uterine des!ent into the pelvi! !avit. as the fetal presentin$ part settles into the pelvis usuall. o!!urs 1 +ee's before the onset of labor in nulliparas Overlap rlappin pin$ $ of !ra !ranial nial bones bones or sha shapin pin$ $ of the fetal hea head d to mold mo ldin ing g Ove a!!o**odate and !onfor* to the bon. and soft parts of the *other2s birth !anal durin$ labor position Relationship of a referen!e point on the presentin$ part of the fetus% su!h as the o!!iput% sa!ru*% !hin% or s!apula% to its lo!ation in the front% ba!'% or sides of the *aternal pelvis presentation That part of the fetus that first enters the pelvis and lies over the inlet *a. be head% fa!e% bree!h% or shoulder presenting part That part of the fetus that lies !losest to the internal os of the !ervi& station Relationship of the presentin$ fetal part to an i*a$inar. line dra+n bet+een the is!hial spines of the pelvis S*al alles lestt di dia* a*ete eterr of th thee fe fetal tal he head ad suboc su boccip cipito itobr breg egmat matic ic dia diamet meter er S* follo+s a line dra+n fro* the *iddle of the anterior fontanel to the undersurfa!e of the o!!ipital bone 1
Valsalva maneuver maneuver An. for!ed e&pirator. effort a$ainst a !losed air+a. su!h as holdin$ one2s breath and ti$htenin$ the abdo*inal *us!les "e#$#% pushin$ durin$ the se!ond sta$e of labor( vertex 3ro+n% or top% of the head
Durin$ late pre$nan!.% the +o*an and fetus prepare for the labor pro!ess# The fetus has $ro+n and developed in preparation for e&trauterine life# The +o*an has under$one various ph.siolo$i! adaptations durin$ pre$nan!. that prepare her for birth and *otherhood# )abor and birth represent the end of pre$nan!.% the be$innin$ of e&trauterine life for the ne+born% and a !han$e in the lives of the fa*il.# This !hapter !ha pter dis dis!us !usses ses the fa!t fa!tors ors aff affe!ti e!tin$ n$ lab labor or%% the pro pro!ess !ess inv involv olved% ed% the nor nor*al *al pro$ression of events% and the adaptations *ade b. both the +o*an and fetus# fetus # FAC!"# AFF$C%&' LAB!" At least five fa!tors affe!t the pro!ess of labor and birth# These are easil. re*e*bered as the five 42s5 passen$er "fetus and pla!enta(% passa$e+a. "birth !anal(% po+ers "!ontra!tions(% position of the *other% and ps.!holo$i! response# The The first four fa!tors are presented here as the basis of understandin$ the ph.siolo$i! pro!ess of labor# The fifth fa!tor is dis!ussed in 3hapter 61# Other fa!tors su!h as pla!e of birth% preparation% t.pe of provider% and pro!edures i*ple*ented *a. *a . be i*portant as +ell ",ande,usse% 6777(# PA##$&'$" Thee +a Th +a. . th thee pa pass ssen en$e $er% r% or fe fetu tus% s% *o *ove vess th thro rou$ u$h h th thee bi birt rth h !a !ana nall is deter*ined b. several intera!tin$ fa!tors5 the si-e of the fetal head% fetal presentation% fetal lie% fetal attitude% and fetal position# /e!ause the pla!enta *ust also pass throu$h the birth !anal% it !an be !onsidered a passen$er alon$ +ith the fetus# 8o+ever% the pla!enta rarel. i*pedes the pro!ess of labor in nor*al va$inal birth% e&!ept in !ases of pla!enta previa#
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#i(e of the fetal head Fig. ) Fetal head at ter*# A% /ones# /% Sutures and fontanels
/e!ause of its si-e and relative ri$idit.% the fetal head has a *a0or effe!t on the birth pro!ess# The fetal s'ull is !o*posed of t+o parietal bones% t+o te*poral bones% the frontal bone% and the o!!ipital bone "Fi$# 6% A). These bones are united b. *e*branous sutures5 the sa$ittal% la*bdoidal% !oronal% and frontal "Fi$# 6% B). Me*branefilled spa!es !alled fontanels are lo!ated +here the sutures interse!t# Durin$ labor% after rupture of *e*branes% palpation of fontanels and sutures durin$ va$inal e&a*ination reveals fetal presentation% position% and attitude# The t+o *ost i*portant fontanels are the anterior and posterior ones "see Fi$# 6% B). The lar$er of these% the anterior fontanel% is dia*ond shaped% is appro&i*atel. 9 b. 1 !* in si-e% and lies at the 0un!tion of the sa$ittal% !oronal% and frontal sutures# It !loses b. 6: *onths after birth# The posterior fontanel lies at the 0un!tion of the sutures of the t+o parietal bones and the one o!!ipital bone% is trian$ular in shape% and is appro&i*atel. 6 b. 1 !* in si-e# It !loses ; to : +ee's after birth# Sutures and fontanels *a'e the s'ull fle&ible to a!!o**odate the infant brain% +hi!h !ontinues to $ro+ for so*e ti*e after birth# /e!ause the bones are not fir*l. united% ho+ever% sli$ht overlappin$ of the bones% or molding of the shape of the head% o!!urs durin$ labor# This !apa!it. of the bones to slide over one another also per*its adaptation to the various dia*eters of the *aternal pelvis# Moldin$ !an be e&tensive% but the heads of *ost ne+borns assu*e their nor*al shape +ithin 9 da.s of birth# Althou$h the si-e of the fetal shoulders *a. affe!t passa$e% their position !an be altered relativel. easil. durin$ labor therefore one shoulder *a. o!!up. a lo+er level than the other# This !reates a shoulder dia*eter that is s*aller than the s'ull% fa!ilitatin$ passa$e throu$h the birth !anal# The !ir!u*feren!e of the fetal hips is usuall. s*all enou$h not to !reate proble*s#
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Fetal presentation
* Fi$# E&a*ples of fetal verte& "o!!iput( presentations in relation to front% ba!'% or side of *aternal pelvis#
Fig. + Fetal presentations# A<3% /ree!h "sa!ral( presentation# D% Shoulder presentation#
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Presentation refers to the part of the fetus that enters the pelvi! inlet first and leads throu$h the birth !anal durin$ labor at ter*# The three *ain presentations are cephalic presentation "head first(% o!!urrin$ in 7;= of births "Fi$# 1( breech presentation "butto!'s or feet first(% o!!urrin$ in 9= of births "Fi$# 9% A-C); and shoulder presentation% seen in 6= of births "Fi$# 9% D). Presenting part refers to that part of the fetal bod. first felt b. the e&a*inin$ fin$er durin$ a va$inal e&a*ination# In a !ephali! presentation% the presentin$ part is usuall. the o!!iput in a bree!h presentation% it is the sa!ru* in the shoulder presentation% it is the s!apula# >hen the presentin$ part is the o!!iput% the presentation is noted as vertex "see Fi$# 1(# Fa!tors that deter*ine the presentin$ part in!lude fetal lie% fetal attitude% and e&tension or fle&ion of the fetal head# Fetal lie Lie is the relationship of the lon$ a&is "spine( of the fetus to the lon$ a&is "spine( of the *other# There are t+o pri*ar. lies5 lon$itudinal% or verti!al% in +hi!h the lon$ a&is of the fetus is parallel +ith the lon$ a&is of the *other "see Fi$# 66<1( and transverse% hori-ontal% or oblique% in +hi!h the lon$ a&is of the fetus is at a ri$ht an$le dia$onal to the lon$ a&is of the *other "see Fi$# 9% D). )on$itudinal lies are either !ephali! or bree!h presentations% dependin$ on the fetal stru!ture that first enters the *other2s pelvis# ,a$inal birth !annot o!!ur +hen the fetus sta.s in a transverse lie# An oblique lie is less !o**on and usuall. !onverts to a lon$itudinal or transverse lie durin$ labor "3unnin$ha* et al#% 1??6(# Fetal attitude Fig. , Dia*eters of the fetal head at ter*# A% 3ephali! presentations5 o!!iput% verte&% and sin!iput and !ephali! dia*eters5 subo!!ipitobre$*ati!% o!!ipitofrontal% and o!!ipito*ental# /% /iparietal dia*eter#
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F F
Fig. - 8ead enterin$ pelvis# /iparietal dia*eter is indi!ated +ith shading "7#1@ !*(# A% Subo!!ipitobre$*ati! dia*eter5 !o*plete fle&ion of head on !hest so that s*allest dia*eter enters# /% O!!ipitofrontal dia*eter5 *oderate e&tension "*ilitar. attitude( so that lar$e dia*eter enters# 3% O!!ipito*ental dia*eter5 *ar'ed e&tension "defle!tion( so that lar$est dia*eter% +hi!h is too lar$e to per*it head to enter pelvis% is presentin$# Attitude is the relationship of the fetal bod. parts to ea!h other# The fetus assu*es a !hara!teristi! posture "attitude( in utero partl. be!ause of the *ode of fetal $ro+th and partl. be!ause of the +a. the fetus !onfor*s to the shape of the uterine !avit.# Nor*all.% the ba!' of the fetus is rounded so that the !hin is fle&ed on the !hest% the thi$hs are fle&ed on the abdo*en% and the le$s are fle&ed at the 'nees# The ar*s are !rossed over the thora&% and the u*bili!al !ord lies bet+een the ar*s and the le$s# This attitude is ter*ed general flexion "see Fi$# 1(# Deviations fro* the nor*al attitude *a. !ause diffi!ulties in !hildbirth# For e&a*ple% in a !ephali! presentation% the fetal head *a. be e&tended or fle&ed in a *anner that presents a head dia*eter that e&!eeds the li*its of the *aternal pelvis% leadin$ to prolon$ed labor% for!eps< or va!uu*
!* at ter*(# >hen the head is in !o*plete fle&ion% this dia*eter allo+s the fetal head to pass throu$h the true pelvis easil. "Fi$s# % A, and @% A). As the head is *ore e&tended% the anteroposterior dia*eter +idens and the head *a. not be able to enter the true pelvis "Fi$# @% B and 3(# Fetal position The presentation or presentin$ part indi!ates that portion of the fetus that overlies the pelvi! inlet# Position is the relationship of the presentin$ part "o!!iput% sa!ru*% *entu* B!hinC% or sin!iput Bdefle&ed verte&C( to the four quadrants of the *other2s pelvis "see Fi$# 1(# 4osition is denoted b. a three
Fi$# ; Stations of presentin$ part% or de$ree of des!ent# /iparietal dia*eter of the fetal head is 0ust belo+ the level of the is!hial spines% bet+een station ? and station 6# #tation is the relationship of the presentin$ part of the fetus to an i*a$inar. line dra+n bet+een the *aternal is!hial spines and is a *easure of the de$ree of des!ent of the presentin$ part of the fetus throu$h the birth !anal# The pla!e*ent of the presentin$ part is *easured in !enti*eters above or belo+ the is!hial spines "Fi$# ;(# For e&a*ple% +hen the lo+er*ost portion of the presentin$ part is 6 !* above the spines% it is noted as bein$ *inus "( 6# At the level of the spines% the station is referred to as ? "-ero(# >hen the presentin$ part is 6 !* belo+ the spines% the station is said to be plus "( 6# /irth is i**inent +hen the presentin$ part is at to @ !*# The station of the presentin$ part should be deter*ined +hen labor be$ins so that the rate of des!ent of the fetus durin$ labor !an be a!!uratel. deter*ined# $ngagement is the ter* used to indi!ate that the lar$est transverse dia*eter 7
of the presentin$ part "usuall. the biparietal dia*eter( has passed throu$h the *aternal pelvi! bri* or inlet into the true pelvis and usuall. !orresponds to station ?# En$a$e*ent often o!!urs in the +ee's 0ust before labor be$ins in pri*i$ravidas and *a. o!!ur before labor or durin$ labor in *ulti$ravidas# En$a$e*ent !an be deter*ined b. abdo*inal or va$inal e&a*ination# PA##A'$/A0 The passa$e+a.% or birth !anal% is !o*posed of the *other2s ri$id bon. pelvis and the soft tissues of the !ervi&% pelvi! floor% va$ina% and introitus "the e&ternal openin$ to the va$ina(# Althou$h the soft tissues% parti!ularl. the *us!ular la.ers of the pelvi! floor% !ontribute to va$inal birth of the fetus% the *aternal pelvis pla.s a far $reater role in the labor pro!ess be!ause the fetus *ust su!!essfull. a!!o**odate itself to this relativel. ri$id passa$e+a.# Therefore the si-e and shape of the pelvis *ust be deter*ined before !hildbirth be$ins# Bony pelvis
Fi$ # Fe*ale pelvis# A% 4elvi! bri* above# /% 4elvi! outlet fro* belo+# The anato*. of the bon. pelvis is des!ribed in 3hapter # The follo+in$ dis!ussion fo!uses on the i*portan!e of pelvi! !onfi$urations as the. relate to the labor pro!ess# "It *a. be helpful to refer to Fi$# #( The bon. pelvis is for*ed b. the fusion of the iliu*% is!hiu*% pubis% and sa!ral bones# The four pelvi! 0oints are the s.*ph.sis pubis% the ri$ht and left sa!roilia! 0oints% and the sa!ro!o!!.$eal 0oint "Fi$# % A). The bon. pelvis is separated b. the bri*% or inlet% into t+o parts5 the false pelvis and the true pelvis# The false pelvis is that part above the bri* and pla.s no part in !hildbearin$# The true pelvis% that part involved in birth% is divided into three planes5 the inlet% or bri* the *idpelvis% or !avit. and the outlet# The pelvi! inlet% +hi!h is the upper border of the true pelvis% is for*ed anteriorl. b. the upper *ar$ins of the pubi! bone% laterall. b. the iliope!tineal lines alon$ the inno*inate bones% and posteriorl. b. the anterior% upper *ar$in of the sa!ru* and the sa!ral pro*ontor.# 8
The pelvi! !avit.% or *idpelvis% is a !urved passa$e havin$ a short anterior +all and a *u!h lon$er !on!ave posterior +all# It is bounded b. the posterior aspe!t of the s.*ph.sis pubis% the is!hiu*% a portion of the iliu*% the sa!ru*% and the !o!!. The pelvi! outlet is the lo+er border of the true pelvis# ,ie+ed fro* belo+% it is ovoid% so*e+hat dia*ond shaped% bounded b. the pubi! ar!h anteriorl.% the is!hial tuberosities laterall.% and the tip of the !o!!.& posteriorl. "Fi$# % B). In the latter part of pre$nan!. the !o!!.& is *ovable "unless it has been bro'en in a fall durin$ s'iin$ or s'atin$% for e&a*ple% and has fused to the sa!ru* durin$ healin$(# Fi$# : 4elvi! !avit.# A% Inlet and *idplane# Outlet not sho+n# /% 3avit. of true pelvis# 3% Note !urve of sa!ru* and a&is of birth !anal# The pelvi! !anal varies in si-e and shape at various levels# The dia*eters at the plane of the pelvi! inlet% *idpelvis% and outlet% plus the a&is of the birth !anal "Fi$# :(% deter*ine +hether va$inal birth is possible and the *anner b. +hi!h the fetus *a. pass do+n the birth !anal# The subpubi! an$le% +hi!h deter*ines the t.pe of pubi! ar!h% to$ether +ith the len$th of the pubi! ra*i and the intertuberous dia*eter% is of $reat i*portan!e# /e!ause the fetus *ust first pass beneath the pubi! ar!h% a narro+ subpubi! an$le +ill be less a!!o**odatin$ than a rounded% +ide ar!h# The *ethod of *easure*ent of the subpubi! ar!h is sho+n in Fi$# 7# A su**ar. of obstetri! *easure*ents is $iven in Table 6#
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Fi$# 7 Esti*ation of an$le of subpubi! ar!h# Gsin$ both thu*bs% e&a*iner e&ternall. tra!es des!endin$ ra*ido+n to tuberosities# "Fro* /ar'aus'as% ,#% /au*ann% )% H Darlin$< Fisher% 3# B1??1C% $eal%h and ph&sical assess'en% B9rd ed#C# St# )ouis5 Mosb.#(
able ) !bstetric Measurements PLA&$
1%AM$$"
Inlet "superior strait( 3on0u$ates Dia$onal Obstetri!5 *easure*ent that deter*ines +hether presentin$ part !an en$a$e or enter superior strait True "vera( "anteroposterior(
61#@<69 !* 6#@<1 !* less than dia$onal "radio$raphi!(
M$A#2"$M$&#
66 !* "61#@( "radio$raphi!(
)en$th of dia$onal !on0u$ate "solid !olored line( !on0u$ate "bro'en !olored line(% and true !on0u$ line(J
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Midplane 6?#@ !* Transverse dia*eter "interspinous dia*eter( The *idplane of the pelvis nor*all. is its lar$est plane and the one of $reatest dia*eter#
Measure*ent of interspinous dia*eterJ
Outlet : !* Transverse dia*eter "intertuberous dia*eter( "biis!hial( The outlet presents the s*allest plane of the pelvi! !anal#
Gse of Thorn2s pelvi*eter to *easure intertuberous dia*eterJ
The four basi! t.pes of pelvis are !lassified as follo+s5 6# L.ne!oid "the !lassi! fe*ale t.pe( 1# Android "rese*blin$ the *ale pelvis( 9# Anthropoid "rese*blin$ the pelvis of anthropoid apes( # 4lat.pelloid "the flat pelvis(
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The $.ne!oid pelvis is the *ost !o**on% +ith *a0or $.ne!oid pelvi! features present in @?= of all +o*en# Anthropoid and android features are less !o**on% and plat.pelloid pelvi! features are the least !o**on# Mi&ed t.pes of pelves are *ore !o**on than pure t.pes "3unnin$ha* et al#% 1??6(# E&a*ples of pelvi! variations and their effe!ts on *ode of birth are $iven in Table 1#
Assess*ent of the bon. pelvis !an be perfor*ed durin$ the first prenatal evaluation and need not be repeated if the pelvis is of adequate si-e and suitable shape# In the third tri*ester of pre$nan!.% the e&a*ination of the bon. pelvis *a. be *ore thorou$h and the results *ore a!!urate be!ause there is rela&ation and in!reased *obilit. of the pelvi! 0oints and li$a*ents due to hor*onal influen!es# >idenin$ of the 0oint of the s.*ph.sis pubis and the resultin$ instabilit. *a. !ause pain in an. or all of the pelvi! 0oints# /e!ause the e&a*iner does not have dire!t a!!ess to the bon. stru!tures and be!ause the bones are !overed +ith var.in$ a*ounts of soft tissue% esti*ates of si-e and shape are appro&i*ate# 4re!ise bon. pelvis *easure*ents !an be deter*ined b. use of !o*puted to*o$raph.% ultrasound% or &
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thi!'ens and its a!!o**odatin$ !apa!it. is redu!ed# The !ontra!tions of the uterine bod. thus e&ert do+n+ard pressure on the fetus% pushin$ it a$ainst the !ervi The !ervi& effa!es "thins( and dilates "opens( suffi!ientl. to allo+ the first fetal portion to des!end into the va$ina# As the fetus des!ends% the !ervi& is a!tuall. dra+n up+ard and over this first portion#
Fig. )3 Gterus in nor*al labor in earl. first sta$e "A( and in se!ond sta$e "/(# 4assive se$*ent is derived fro* lo+er uterine se$*ent "isth*us( and !ervi&% and ph.siolo$i! retra!tion is derived fro* anato*i! internal os# 3% Gterus in abnor*al labor in se!ond
The pelvi! floor is a *us!ular la.er that separates the pelvi! !avit. above fro* the perineal spa!e belo+# This stru!ture helps the fetus rotate anteriorl. as it passes throu$h the birth !anal# As noted earlier% the soft tissues of the va$ina develop throu$hout pre$nan!. until at ter* the va$ina !an dilate to a!!o**odate the fetus and per*it passa$e of the fetus to the e&ternal +orld# P!/$"# Involuntar. and voluntar. po+ers !o*bine to e&pel the fetus and the pla!enta fro* the uterus# Involuntar. uterine !ontra!tions% ter*ed the pri'ar& poers, si$nal the be$innin$ of labor# On!e the !ervi& has dilated% voluntar. bearin$do+n efforts b. the +o*an% ter*ed the secondar& poers, au$*ent the for!e of the involuntar. !ontra!tions# Primary po4ers The involuntar. !ontra!tions ori$inate at !ertain pa!e*a'er points in the thi!'ened *us!le la.ers of the upper uterine se$*ent# Fro* the pa!e*a'er points% !ontra!tions *ove do+n+ard over the uterus in +aves% separated b. short rest periods# Ter*s used to des!ribe these involuntar. !ontra!tions in!lude freuenc& "the ti*e fro* the be$innin$ of one !ontra!tion to the be$innin$ of the ne&t(% dura%ion
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"len$th of !ontra!tion(% and in%ensi%& "stren$th of !ontra!tion(# The pri*ar. po+ers are responsible for the effa!e*ent and dilation of the !ervi& and des!ent of the fetus# $ffacement of the !ervi& *eans the shortenin$ and thinnin$ of the !ervi& durin$ the first sta$e of labor# The !ervi&% nor*all. 1 to 9 !* lon$ and appro&i*atel. 6 !* thi!'% is obliterated or ta'en up b. a shortenin$ of the uterine *us!le bundles durin$ the thinnin$ of the lo+er uterine se$*ent that o!!urs in advan!in$ labor# Onl. a thin ed$e of the !ervi& !an be palpated +hen effa!e*ent is !o*plete# Effa!e*ent $enerall. is advan!ed in first
Fi$# 66 3ervi!al effa!e*ent and dilation# Note ho+ !ervi& is dra+n up around presentin$ part "internal os(# Me*branes are inta!t and head is not +ell applied to !ervi A% /efore labor# /% Earl. effa!e*ent# 3% 3o*plete effa!e*ent "6??=(# 8ead is +ell applied to !ervi D% 3o*plete dilation "6? !*(# There is so*e overlappin$ of !ranial bones and *e*branes are still inta!t# 1ilation of the !ervi& is the enlar$e*ent or +idenin$ of the !ervi!al openin$ and the !ervi!al !anal that o!!urs on!e labor has be$un# The dia*eter of the !ervi& in!reases fro* less than 6 !* to full dilation "appro&i*atel. 6? !*( to allo+ birth of a ter* fetus# >hen the !ervi& is full. dilated "and !o*pletel. retra!ted(% it !an no lon$er be palpated "Fi$# 66 D). Full !ervi!al dilation *ar's the end of the first sta$e of labor# Dilation of the !ervi& o!!urs b. the dra+in$ up+ard of the *us!ulofibrous !o*ponents of the !ervi& that is !aused b. stron$ uterine !ontra!tions# 4ressure e&erted b. the a*nioti! fluid +hile the *e*branes are inta!t or b. the for!e applied b. the presentin$ part also !an pro*ote !ervi!al dilation# S!arrin$ of the !ervi& as a result of prior infe!tion or sur$er. *a. slo+ !ervi!al dilation# In the first and se!ond sta$es of labor% in!reased intrauterine pressure !aused
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b. !ontra!tions e&erts pressure on the des!endin$ fetus and the !ervi >hen the presentin$ part of the fetus rea!hes the perineal floor% *e!hani!al stret!hin$ of the !ervi& o!!urs# Stret!h re!eptors in the posterior va$ina !ause release of endo$enous o&.to!in that tri$$ers the *aternal ur$e to bear do+n% or the Ferguson reflex. Gterine !ontra!tions are usuall. independent fro* e&ternal for!es# For e&a*ple% laborin$ +o*en +ho are paraple$i! +ill have nor*al but painless uterine !ontra!tions "3unnin$ha* et al#% 1??6(# Gterine !ontra!tions *a. de!rease te*poraril. in frequen!. and intensit. if nar!oti! anal$esi! *edi!ation or epidural anal$esia is $iven earl. in labor "Ale&ander et al#% 677:(# The e&a!t relationship bet+een prolon$ed labor and epidural anal$esia !ontinues to be investi$ated "Tho*pson et al#% 677:(# #econdary po4ers As soon as the presentin$ part rea!hes the pelvi! floor the !ontra!tions !han$e in !hara!ter and be!o*e e&pulsive# The laborin$ +o*an e&perien!es an involuntar. ur$e to push# She uses se!ondar. po+ers "bearin$oolle.% 677;(# >hen and ho+ a +o*an pushes in se!ond sta$e is a *u!hoolle.% 677; Sa*pselle% 6777 Tho*son% 677@(# Althou$h no si$nifi!ant differen!es have been found in the duration of se!ond
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Fig. )* 4ositions for labor and birth# A% 4ositions for labor# /% 4ositions for $ivin$ birth#
4osition affe!ts the +o*an2s anato*i! and ph.siolo$i! adaptations to labor# Frequent !han$es in position relieve fati$ue% in!rease !o*fort% and i*prove !ir!ulation# Therefore a laborin$ +o*an should be en!oura$ed to find positions that are *ost !o*fortable to her "Fi$# 61% A) "see Resear!h bo&(#
An upri$ht position "+al'in$% sittin$% 'neelin$% or squattin$( offers a nu*ber of advanta$es# Lravit. !an pro*ote the des!ent of the fetus# Gterine !ontra!tions are $enerall. stron$er and *ore effi!ient in effa!in$ and dilatin$ the !ervi&% resultin$ in shorter labor "Sher*er H Raines% 677 Si*'in H An!heta% 1???(# An upri$ht position is also benefi!ial to the *other2s !ardia! output% +hi!h nor*all. in!reases durin$ labor as uterine !ontra!tions return blood to the vas!ular bed# The in!reased !ardia! output i*proves blood flo+ to the uteropla!ental unit and the *aternal 'idne.s# 3ardia! output is !o*pro*ised if the des!endin$ aorta and as!endin$ vena !ava are !o*pressed durin$ labor# 3o*pression of these *a0or vessels *a. result in supine h.potension that de!reases pla!ental perfusion# >ith the +o*an in an upri$ht position% pressure on the *aternal vessels is redu!ed and !o*pression is prevented# If the +o*an +ishes to lie do+n% a lateral position is su$$ested "3unnin$ha* et al#% 1??6(# The all fours position "hands and 'nees( *a. be used to relieve ba!'a!he if the fetus is in an o!!ipitoposterior position and *a. assist in anterior rotation of the fetus and in !ases of shoulder d.sto!ia "Si*'in 677@ Si*'in H An!heta% 1???(# 4ositionin$ for se!ond
+o*an2s preferen!e% but it is !onstrained b. the !ondition of the +o*an or fetus% the environ*ent% and the health !are provider2s !onfiden!e in assistin$ in a birth in a spe!ifi! position "Si*'in H An!heta% 1???(# The predo*inant position in the Gnited States in ph.si!ianoolle.% 677; Si*'in H An!heta% 1???(# There is no eviden!e that an. of these positions su$$ested for se!ond
effa!ed and *a. be$in to dilate# The *e*branes *a. rupture spontaneousl.# Other pheno*ena are !o**on in the da.s pre!edin$ labor5 "6( loss of ?#@ to 6#@ '$ in +ei$ht% !aused b. +ater loss resultin$ fro* ele!trol.te shifts that in turn are produ!ed b. !han$es in estro$en and pro$esterone levels and "1( a sur$e of ener$.# >o*en spea' of havin$ a burst of ener$. that the. often use to !lean the house and put ever.thin$ in order# )ess !o**onl.% so*e +o*en e&perien!e diarrhea% nausea% vo*itin$% and indi$estion ",arne.% 677(# /o& 6 lists si$ns that *a. pre!ede labor#
Box ) #igns Preceding Labor
)i$htenin$ Return of urinar. frequen!. /a!'a!he Stron$er /ra&ton 8i!'s !ontra!tions >ei$ht loss ?#@<6#@ '$ Sur$e of ener$. In!reased va$inal dis!har$e blood. sho+ 3ervi!al ripenin$ Me*branes *a. rupture !$ !F LAB!" The onset of true labor !annot be as!ribed to a sin$le !ause# Man. fa!tors% in!ludin$ !han$es in the *aternal uterus% !ervi&% and pituitar. $land% are involved# 8or*ones produ!ed b. the nor*al fetal h.pothala*us% pituitar.% and adrenal !orte& probabl. !ontribute to the onset of labor# 4ro$ressive uterine distention% in!reasin$ intrauterine pressure% and a$in$ of the pla!enta see* to be asso!iated +ith in!reasin$ *.o*etrial irritabilit.# This is a result of in!reased !on!entrations of estro$en and prosta$landins% as +ell as de!reasin$ pro$esterone levels# The *utuall. !oordinated effe!ts of these fa!tors result in the o!!urren!e of stron$% re$ular% rh.th*i! uterine !ontra!tions# Nor*all.% the out!o*e of these fa!tors +or'in$ to$ether is the birth of the fetus and the e&pulsion of the pla!enta# 8o+ever% it is still not !o*pletel. understood ho+ !ertain alterations tri$$er others and ho+ proper !he!'s and balan!es are *aintained# Fetal fibrone!tin is a protein found in plas*a and !ervi!ova$inal se!retions of pre$nant +o*en before the onset of labor# Assess*ent for the presen!e of fetal fibrone!tin is bein$ used to predi!t the li'elihood of preter* labor in +o*en +ho are at in!reased ris' for this !o*pli!ation# The value of dete!tion of fetal fibrone!tin in *ana$e*ent of +o*en +ith preter* labor has .et to be deter*ined "3ole*an et al#% 677: Loldenber$ et al% 1???(# #A'$# !F LAB!" )abor is !onsidered nor*al +hen the +o*an is at or near ter*% no !o*pli!ations e&ist% a sin$le fetus presents b. verte&% and labor is !o*pleted +ithin 1 hours# The !ourse of nor*al labor% +hi!h is re*ar'abl. !onstant% !onsists of "6(
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re$ular pro$ression of uterine !ontra!tions% "1( effa!e*ent and pro$ressive dilation of the !ervi&% and "9( pro$ress in des!ent of the presentin$ part# Four sta$es of labor are re!o$ni-ed# These sta$es are dis!ussed in $reater detail% alon$ +ith nursin$ !are for the laborin$ +o*an and fa*il.# The first sta$e of labor is !onsidered to last fro* the onset of re$ular uterine !ontra!tions to full dilation of the !ervi The onset of labor is often diffi!ult to establish be!ause the +o*an *a. be ad*itted to the labor unit 0ust before birth and the be$innin$ of labor *a. be onl. an esti*ate# The first sta$e is *u!h lon$er than the se!ond and third !o*bined# Lreat variabilit. is the rule% ho+ever% dependin$ on the fa!tors dis!ussed previousl. in this !hapter# Full dilation *a. o!!ur in less than 6 hour in so*e *ultiparous pre$nan!ies# In first
as abnor*al bleedin$# M$C5A&%#M !F LAB!" Fig. )+ 3ardinal *ove*ents of the *e!hanis* of labor# )eft o!!ipitoanterior ")OA( presentation# A% En$a$e*ent and des!ent# /% Fle&ion# 3% Internal rotation to o!!ipitoanterior position "OA(# D% E&tension# E% E&ternal rotation be$innin$ "restitution(# F% E&ternal rotation#
As alread. dis!ussed% the fe*ale pelvis has varied !ontours and dia*eters at different levels% and the presentin$ part of the passen$er is lar$e in proportion to the passa$e# Therefore% for va$inal birth to o!!ur% the fetus *ust adapt to the birth !anal durin$ the des!ent# The turns and other ad0ust*ents ne!essar. in the hu*an birth pro!ess are ter*ed the 'echanis' of labor "Fi$# 69(# The seven !ardinal *ove*ents of the *e!hanis* of labor that o!!ur in a verte& presentation are en$a$e*ent% des!ent% fle&ion% internal rotation% e&tension% e&ternal rotation "restitution(% and finall. birth b. e&pulsion# Althou$h these *ove*ents are dis!ussed separatel.% in a!tualit. a !o*bination of *ove*ents o!!urs si*ultaneousl.# For e&a*ple% en$a$e*ent involves both des!ent and fle&ion# $ngagement >hen the biparietal dia*eter of the head passes the pelvi! inlet% the head is said to be engaged in the pelvi! inlet "see Fi$# 69% A). In *ost nulliparous pre$nan!ies this o!!urs before the onset of a!tive labor be!ause the fir*er abdo*inal *us!les dire!t the presentin$ part into the pelvis# In *ultiparous pre$nan!ies% in +hi!h the abdo*inal *us!ulature is *ore rela&ed% the head often re*ains freel. *ovable above the pelvi! bri* until labor is established# Asynclitism. The head usuall. en$a$es in the pelvis in a s.n!liti! position% one that is parallel to the anteroposterior plane of the pelvis# Frequentl. asynclitism o!!urs "the head is defle!ted anteriorl. or posteriorl. in the pelvis(% +hi!h !an fa!ilitate des!ent be!ause the head is bein$ positioned to a!!o**odate to the pelvi! !avit. "Fi$# 6(# 8o+ever% e&tre*e as.n!litis* !an !ause !ephalopelvi! disproportion% even in a nor*al
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!annot des!end#
Fig. ), S.n!litis* and as.n!litis*# A% Anterior as.n!litis*# /% Nor*al s.n!litis*# 3% 4osterior as.n!litis*# 1escent Descen% refers to the pro$ress of the presentin$ part throu$h the pelvis# Des!ent depends on at least four for!es5 "6( pressure e&erted b. the a*nioti! fluid% "1( dire!t pressure e&erted b. the !ontra!tin$ fundus on the fetus% "9( for!e of the !ontra!tion of the *aternal diaphra$* and abdo*inal *us!les in the se!ond sta$e of labor% and "( e&tension and strai$htenin$ of the fetal bod.# The effe!ts of these for!es are *odified b. the si-e and shape of the *aternal pelvi! planes and the si-e of the fetal head and its !apa!it. to *old# The de$ree of des!ent is *easured b. the station of the presentin$ part "see Fi$# ;(# As *entioned% little des!ent o!!urs durin$ the latent phase of the first sta$e of labor# Des!ent a!!elerates in the a!tive phase +hen the !ervi& has dilated to @ to !*# It is espe!iall. apparent +hen the *e*branes have ruptured# In a first
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dia*eter "7#@ !*( rather than the lar$er dia*eters to present to the outlet# %nternal rotation The *aternal pelvi! inlet is +idest in the transverse dia*eter# Therefore the fetal head passes the inlet into the true pelvis in the o!!ipitotransverse position# The outlet is +idest in the anteroposterior dia*eter% ho+ever# Therefore% for the fetus to e&it% the head *ust rotate# Internal rotation be$ins at the level of the is!hial spines but is not !o*pleted until the presentin$ part rea!hes the lo+er pelvis# As the o!!iput rotates anteriorl.% the fa!e rotates posteriorl.# >ith ea!h !ontra!tion the fetal head is $uided b. the bon. pelvis and the *us!les of the pelvi! floor# Eventuall.% the o!!iput +ill be in the *idline beneath the pubi! ar!h# The head is al*ost al+a.s rotated b. the ti*e it rea!hes the pelvi! floor "see Fi$# 69% P# /oth the levator ani *us!les and the bon. pelvis are i*portant for a!hievin$ anterior rotation# A previous !hildbirth in0ur. or re$ional anesthesia *a. !o*pro*ise the fun!tion of the levator slin$# $xtension >hen the fetal head rea!hes the perineu* for birth% it is defle!ted anteriorl. b. the perineu*# The o!!iput passes under the lo+er border of the s.*ph.sis pubis first% then the head e*er$es b. e&tension5 first the o!!iput% then the fa!e% and finall. the !hin "see Fi$# 69% D). "estitution and external rotation After the head is born% it rotates briefl. to the position it o!!upied +hen it +as en$a$ed in the inlet# This *ove*ent is ter*ed res%i%u%ion "see Fi$# 69% +). The @hen it rea!hes the outlet% it rotates to the *idline and is delivered fro* under the pubi! ar!h# The posterior shoulder is $uided over the perineu* until it is free of the va$inal introitus# $xpulsion After birth of the shoulders% the head and shoulders are lifted up to+ard the *other2s pubi! bone and the trun' of the bab. is born b. fle&in$ it laterall. in the dire!tion of the s.*ph.sis pubis# >hen the bab. has !o*pletel. e*er$ed% birth is !o*plete% and the se!ond sta$e of labor ends#
P50#%!L!'%C A1APA%! ! LAB!" In addition to the *aternal and fetal anato*i! adaptations that o!!ur durin$ birth% ph.siolo$i! adaptations *ust also o!!ur#
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F$AL A1APA%!& Several i*portant ph.siolo$i! adaptations o!!ur in the fetus# These !han$es o!!ur in fetal heart rate% fetal !ir!ulation% respirator. *ove*ents% and other behaviors# Fetal heart rate Fetal heart rate "F8R( *onitorin$ provides reliable and predi!tive infor*ation about the !ondition of the fetus related to o&.$enation# The avera$e F8R at ter* is 6? beats per *inute "beats*in(# The nor*al ran$e is 66? to 6;? beats*in# Earlier in $estation the F8R is hi$her% +ith an avera$e of appro&i*atel. 6;? beats*in at 1? +ee's of $estation# The rate de!reases pro$ressivel. as the *aturin$ fetus rea!hes ter*# 8o+ever% te*porar. a!!elerations and sli$ht earl. de!elerations of the F8R !an be e&pe!ted in response to spontaneous fetal *ove*ent% va$inal e&a*ination% fundal pressure% uterine !ontra!tions% abdo*inal palpation% and fetal head !o*pression# Stresses to the uterofetopla!ental unit result in !hara!teristi! F8R patterns# Fetal circulation Fetal !ir!ulation !an be affe!ted b. *an. fa!tors% in!ludin$ *aternal position% uterine !ontra!tions% blood pressure% and u*bili!al !ord blood flo+# Gterine !ontra!tions durin$ labor tend to de!rease !ir!ulation throu$h the spiral arterioles and subsequent perfusion throu$h the intervillous spa!e# Most health. fetuses are +ell able to !o*pensate for this stress and e&posure to in!reased pressure +hile *ovin$ passivel. throu$h the birth !anal durin$ labor# Gsuall. u*bili!al !ord blood flo+ is undisturbed b. uterine !ontra!tions or fetal position ")o+e H Reiss% 677;(# Fetal respiration 3ertain !han$es sti*ulate !he*ore!eptors in the aorta and !arotid bodies to prepare the fetus for initiatin$ respirations i**ediatel. after birth ")o+e H Reiss% 677;(# These !han$es in!lude the follo+in$5 Q Fetal lun$ fluid is !leared fro* the air passa$es durin$ labor and "va$inal( birth# Q Fetal o&.$en pressure "4o1( falls# Q Arterial !arbon dio&ide pressure "4!o1( rises# Q Arterial p8 falls# Q /i!arbonate level falls# Q Fetal respirator. *ove*ents de!rease durin$ labor# MA$"&AL A1APA%!& As the +o*an pro$resses throu$h the sta$es of labor% various bod. s.ste*s adapt that !ause the +o*an to e&hibit both ob0e!tive and sub0e!tive s.*pto*s# Cardiovascular changes Durin$ ea!h !ontra!tion% ?? *l of blood is e*ptied fr o* the uterus into the *aternal vas!ular s.ste*# This in!reases !ardia! output b. appro&i*atel. 6?= to
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6@= in the first sta$e and b. appro&i*atel. 9?= to @?= in the se!ond sta$e# The heart rate in!reases sli$htl.# 3han$es in the +o*an2s blood pressure also o!!ur# /lood flo+% +hi!h is redu!ed in the uterine arter. b. !ontra!tions% is redire!ted to peripheral vessels# As a result% peripheral resistan!e in!reases% and blood pressure rises "3ha*berlain H 4ip'in% 677:(# Durin$ the first sta$e of labor% uterine !ontra!tions !ause s.stoli! readin$s to rise b. appro&i*atel. 6? ** 8$# Therefore assessin$ blood pressure bet+een !ontra!tions provides *ore a!!urate readin$s ",arne.% 677(# Durin$ the se!ond sta$e% !ontra!tions *a. !ause s.stoli! pressures to in!rease b. 9? ** 8$ and diastoli! readin$s to in!rease b. 1@ ** 8$% +ith both s.stoli! and diastoli! pressures re*ainin$ so*e+hat elevated even bet+een !ontra!tions# Therefore the +o*an alread. at ris' for h.pertension is at in!reased ris' for !o*pli!ations su!h as !erebral he*orrha$e# Supine h.potension "see Fi$# ( o!!urs +hen the as!endin$ vena !ava and des!endin$ aorta are !o*pressed# The laborin$ +o*an is at $reater ris' for supine h.potension if the uterus is parti!ularl. lar$e be!ause of *ultifetal pre$nan!.% h.dra*nios% or obesit. or if the +o*an is deh.drated or h.povole*i!# In addition% an&iet. and pain% as +ell as so*e *edi!ations% !an !ause h.potension# The +o*an should be dis!oura$ed fro* usin$ the Valsalva maneuver "holdin$ one2s breath and ti$htenin$ abdo*inal *us!les( for pushin$ durin$ the se!ond sta$e# This a!tivit. in!reases intrathora!i! pressure% redu!es venous return% and in!reases venous pressure# The !ardia! output and blood pressure in!rease and the pulse slo+s te*poraril.# Durin$ the ,alsalva *aneuver% fetal h.po&ia *a. o!!ur# The pro!ess is reversed +hen the +o*an ta'es a breath# The +hite blood !ell ">/3( !ount !an in!rease "4a$ana H 4a$ana% 1??6(# Althou$h the *e!hanis* leadin$ to this in!rease in >/3s is un'no+n% it *a. be se!ondar. to ph.si!al or e*otional stress or to tissue trau*a# )abor is strenuous% and ph.si!al e&er!ise alone !an in!rease the >/3 !ount# So*e peripheral vas!ular !han$es o!!ur% perhaps in response to !ervi!al dilation or to !o*pression of *aternal vessels b. the fetus passin$ throu$h the birth !anal# Flushed !hee's% hot or !old feet% and eversion of he*orrhoids *a. result# "espiratory changes In!reased ph.si!al a!tivit. +ith $reater o&.$en !onsu*ption is refle!ted in an in!rease in the respirator. rate# 8.perventilation *a. !ause respirator. al'alosis "an in!rease in p8(% h.po&ia% and h.po!apnia "de!rease in !arbon dio&ide(# In the un*edi!ated +o*an in the se!ond sta$e% o&.$en !onsu*ption al*ost doubles# An&iet. also in!reases o&.$en !onsu*ption# "enal changes Durin$ labor% spontaneous voidin$ *a. be diffi!ult for various reasons5 tissue ede*a !aused b. pressure fro* the presentin$ part% dis!o*fort% anal$esia% and e*barrass*ent# 4roteinuria of 6 is a nor*al findin$ be!ause it !an o!!ur in response to the brea'do+n of *us!le tissue fro* the ph.si!al +or' of labor#
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%ntegumentary changes The inte$u*entar. s.ste* !han$es are evident% espe!iall. in the $reat distensibilit. "stret!hin$( in the area of the va$inal introitus# The de$ree of distensibilit. varies +ith the individual# Despite this abilit. to stret!h% even in the absen!e of episioto*. or la!erations% *inute tears in the s'in around the va$inal introitus do o!!ur# Musculos8eletal changes The *us!ulos'eletal s.ste* is stressed durin$ labor# Diaphoresis% fati$ue% proteinuria "6(% and possibl. an in!reased te*perature a!!o*pan. the *ar'ed in!rease in *us!le a!tivit.# /a!'a!he and 0oint a!he "unrelated to fetal position( o!!ur as a result of in!reased 0oint la&it. at ter*# The labor pro!ess itself and the +o*an2s pointin$ her toes !an !ause le$ !ra*ps# &eurologic changes Sensorial !han$es o!!ur as the +o*an *oves throu$h phases of the first sta$e of labor and as she *oves fro* one sta$e to the ne&t# Initiall. she *a. be euphori!# Euphoria $ives +a. to in!reased seriousness% then to a*nesia bet+een !ontra!tions durin$ the se!ond sta$e% and finall. to elation or fati$ue after $ivin$ birth# Endo$enous endorphins "a *orphine
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