Normal Progress of Labour

7/28/2019 Normal Progress of Labour

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Normal Progress of Labour

Moderator : Dr Sunil Gupta


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Normal labour should fulfil following defined criteria1. Spontaneous in onset and at term

2. With vertex presentation .

4. Natural termination with minimal aids5. Without having any complication affecting mother or baby.


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Stages of Labor1st Stage

Interval between onset of true labor pains and ends with fullcervical dilatationAverage duration is about 12 hrs in primigravida / 6 hrs inmulti ravida

2 phases:Latent phase (upto 3 cm cervical dilatation) period between onset of

labor and point at which a change in slope of rate of cervical dilatation isnoted.Active Greater rate of cervical dilatation and usually begins around 2-3cm (upto 10 cm)


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First Stage Latent Phase

Few days leading up to active labourProstaglandin mediated ripening of cervix

Irregular contractions begin effacement oo y s ow mucous an oo w c prev ous y p uggecervix liquefies. Likely also mediated by prostaglandins.Membranes can rupture at any time (often assisted but ARM is

NOT part of normal labour). This event tends to trigger activelabour, again likely due to the release of prostaglandins (truemechanism not fully understood)


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First Stage Active Phase

Said to begin once regular contractions established, or effacedcervix 3cm dilatedCervix dilates at approx 1cm/hr and is incorporated into lowersegment

Upper segment progressively shortens and thickens, due tospirals of smooth muscle contractingLower segment stretches and thins

Ends when cervix is 10cm dilated (Fully)


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To Summarize :Cardinal events in first stage of labour is :

Dilatation of cervixEffacement of cervix

Progressive uterine contraction, progressive dilatation and ultimaterupture of membranesMaternal and fetal conditions remain unchanged except during uterine

contraction


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Second Stage

2nd stageInterval between full cervical dilatation and ends with expulsion of fetus.

Average durationNulli arous 3 hrs w/ e idural; 2 hrs w/o e idural Multiparous 2 hrs w/ epidural; 30 min to 1 hr w/o epidural

Upper segment continues to shorten and thicken. Majority of fetus in lower segment

Head passes intraspinous diameter the narrowest part of thepelvisPerineum softened by congestion with blood (not unlikearousal)Delivery accomplished by the following six manoeuvres:


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Six manoeuvres of delivery1. Engagement of the fetal head in the transverse position. The baby is

looking across the pelvis at one or other of the mother's hips.2. Descent and flexion of the fetal head3. Internal rotation . The fetal head rotates 90 degrees to the occipito-

anterior position so that the baby's face is towards the mother'srectum.

4. Delivery by extension . The fetal head passes out of the birth canal.Its head is tilted backwards so that its forehead leads the way throughthe vagina.

5. Restitution . The fetal head turns through 45 degrees to restore itsnormal relationship with the shoulders, which are still at an angle.

6. External rotation . The shoulders repeat the corkscrew movementsof the head, which can be seen in the final movements of the fetalhead.


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To summarize :Cardinal events :

Descent andDelivery of fetus

Clinical manifestations :

o Bearing down to expulsion of fetus


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Third StageFrom delivery of fetus to delivery of placentaUsually within 15-30 mins (depends on choice of active or expectantmanagement)Immediately after delivery, contractions tend to stop for brief periodPlacenta separated due to shearing effect of uterus contracting after

oetus e vere , t ere y re uc ng s ze o s te o attac mentRetroplacental haematoma forms, exuding downwards pressureActive management is now so common to be considered NORMAL

Oxytotic given to stimulate uterine contraction

Placenta can be delivered by maternal effort or by controlled cord traction (CCT)Active Management has been shown to reduce PPH


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Partograph and Criteria for ActiveLabor

Label with patient identifyinginformation

Note fetal heart rate, color of amniotic fluid, presence of moulding,contraction pattern, medications

given

Alert line starts at 4 cm--from here,expect to dilate at rate of 1 cm/hour

Action line: If patient does notprogress as above, action is required


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Pain pathways during labour


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Sympathetic preganglionic fibres

Afferent pain pathway fromfundus and body of uterusascend to spinal cord through

hypogastric plexus throughposterior roots of T 10, 11, 12.

Parasympathetic preganglionic fibres

S2, S3, S4

Fibres from cervix run in pelvicsplanchnic nerves and enter spinalcord through posterior roots of S2,3, 4


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Pain during the first stage of labourMostly visceral resulting due to uterine contractions andcervical dilatationInitially confined to T11 12 dermatomes (Latent phase)Eventually involves T10 L1 dermatomes (Active phase)Thus the visceral afferent athwa res onsible for labour

pains travel withsympathetic nerve fibresUterine and cervical plexus hypogastric andAortic plexus Enters T10-L1 nerve roots

The pain is primarily in the lower Abdomen but can bereferred to lumbosacral regions, gluteal, and thighs as labourprogress.


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Nulliparous women with history of dysmenorrhoea appear toexperience greater pain during the first stage of labourStudies suggest that women who experience more intense

pain during the latent phase of labour have longer laboursand are more likel to re uire cesarean sections.


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Pain during second stage of labourThe onset of perineal pain at the end of the first stage signalsthe beginning of fetal descent and second stage of labour.Streching and compression of pelvic and perineal structures

intensify the pain . pudendal nerves (S2-4) so pain during the second stage of labour involves the T10-S4 dermatomes.

Studies suggest ---- more rapid fetal descent in multiparouswomen results in more intense pain than more gradual fetaldescent in nulliparous patients.


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The Placenta:Anatomy, Physiology and Transfer of drugs


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Embryology :At Implantation : 6th day after fertilization


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Decidua :After implantation of embryo, uterineendometrium is called decidua .


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Subdivisions of decidua :


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Formation of chorionic villi :Villi are offshoots from thesurface of the trophoblast with the underlying extra-embryonic mesoderm (Chorion)


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Two stages in the formation of chorionic villi :


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Early stages information of chorionic villi :


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Further stages in establishments of chorionic villi :


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Human placenta is haemo choreal

In naming the types of placenta in different species ,two words are used frist wordindicates maternal tissue andsecond fetal tissue. In Haemo choreal placenta

materna tissue is oo anfetal tissue is chorion. Since the Human Heamochoreal placenta lacks maternallayers , the maternal blooddirectly bathes fetal tissues.


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Vascular Architecture :Maternal : Salient features :

Spiral arteries of the uterus becomes elongated and coiledunder hormonal influences.In late pregnancy the growing demands of the developingfetus require the 200 spiral arteries that feed placenta to handle a blood flow of approximately 600 ml/min.

The vasodilation required is the result of replacement of theelastic and muscle components of artery by cytotrophoblast

cells initially and fibroid cells later.This replacement reduces the vasoconstrictor activity of thesearteries.


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Circulation of blood through placenta Blood flow through lacunar spaces inthe syncytiotrophoblast begins as earlyas the 9th day of pregnancy Thereafter, the maternal blood in theintervillous spaces is constantly incirculation.

Blood enters the intervillous spacesthrou h maternal arteries that o en into the space .

The pressure (70 80 mm Hg) of blood drives it right up to the chorionicplate. Blood from the intervillous spaces isdrained trough fenestrations in decidualveins. But as the pregnancy progressessthe total number of veins contributingto blood return is dramatically reduced. In fully formed placenta, theintervillous spaces contain 350 ml of blood which is replaced in 15 to 20 sec.i.e 3 to 4 times per minute.


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Physiology :Barrier function of placenta :

Placenta is an imperfect barrier that allows almost allsubstances to cross, including an occasional red cell.

Placenta contains vast array of cytochrome P450 isoenzymes and decreasing fetal exposure.Thickness of the placental tissues diminishes as gestationprogresses, may influence rate of diffusion


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Hormonal function of placenta :Steroidogenic function of placenta begins by 35 to 47 days afterovulation and the production of estrogen and progestroneexceeds that of corpus leuteum (Ovarian-placental shift)Wide array of enzymes

Binding proteinsPolypeptide hormones

HCG , HPL etc.


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Regulation of Placental Blood flowMaternal blood flow :

Vasodilatation of spiral arteries due to functional denervation of themusculoelastic lining of spiral arteriesMaternal blood enters the intervillous space at 70 to 80 mm Hg

Fetal Blood flow : n contrast to maternop acenta oo ow , etop acenta oo ow

is more the result of vascular growth, rather than vasodilatation.Fetoplacental blood flow is autoregulated but the process is not welldefined.Endothelial derived relaxing factors, especially prostacyclin and nitricoxide is important in fetoplacental circulation.There is evidence to suggest --- hypoxia induced fetoplacentalvasoconstriction and reduction in nitric oxide .


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Transport mechanisms :Passive transport :depends on1. Concentration and electrochemical difference2. Molecular weight3. Lipid solubility4. Level of ionization5. Membrane surface area and thickness

Facilitated transport :-

gradientExhibits:

saturation kinetics,competitive and non competitive inhibition ,stereospecificity and

temperature influencesActive transport : similar to facilitated diffusion but movement of substance can takeplace against concentration gradientPinocytosis : For large macromolecules


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Other factors that influence placental transport :Maternal and fetal blood flowPlacental bindingPlacental metabolism

Maternal and fetal plasma protein bindingGestational age


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Transfer of Respiratory Gases and Nutrients Placenta provides approximately 8mlO2/min/kg fetal weight for fetal growthand development The diagram shows transplacentaldiffusion capacity for oxygen .

Factors affecting the fetal blood PO2 onceit reaches equilibrium in the villi end capillaries are

1. Concurrent and counter current arrangement of maternal and fetal blood flow.

2. Difference between oxyhemoglobin dissociation curvesof maternal and fetal blood

3. Bohr effect may augment the transfer of oxygen acrossthe placenta .

There is double Bohr effect that enhancesthe transfer of oxygen from mother tofetus and accounts 2 to 8% of transplacental transfer of oxygen.


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Glucose transportSimple diffusion alone cannot account for the amount of glucose required to meet demands in fetusStereospecific facilitated diffusion system which is independentof insulin, sodium radient, or cellular ener y has been

describedD-Glucose transport protein have been identifiedOnly 28% of glucose absorbed from the maternal surface if

transferred through the umbilical vein .


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Amino acids :Concentration of amino acids are highest in placenta followed by umbilical venous blood and then maternal blood .

Fatty Acids :Free fatty acids, such as palmitic and linoleic acids , readily crosshuman placenta.


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Drug transfer : Factors affectingdrug transfer acrossthe human placentainclude :

1. Lipid solubility2. Protein binding

3. Tissue binding4. pKa5. pH6. Blood flow


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Normal Progress of Labour