Physiology of normal labour

PHYSIOLOGY OF NORMAL LABOUR

DR RAJEEV SOODASTT. PROF.

DEPT. OF OBG IGMC SHIMLA

PARTURITION is defined as the process of bringing forth of young which comprises of multiple transformations in both uterine and cervical functions

There are four phases :Quiescence Activation phaseStimulation phaseInvolution phase.

PHASES OF PARTURITION

QUIESCENCE ACTIVATION STIMULATION

INVOLUTION

FROM CONCEPTION TO INITIATION OF PARTURITION

BEGINNING OF PARTURITION TO ONSET OF LABOUR

UP TO DELIVERY OF CONCEPTUS

TILL THE TIME FERTILITY IS RESTORED

PREDOMIN-ANTLY INFLUENC -ING FACTOR

INHIBITORSPROGESTRONE , PROSTACYCLIN, NITROUSOXIDE, RELAXIN

UTEROTROPICESTROGEN, OXYTOCIN , PROSTAGLANDINS-> INCREASED GAP JUNC.

UTEROTONICSOXYTOCINPROSTAGLANDINS

OXYTOCINTHROMBINS

UTERINE ACTIVITY

CONTRACTILE UNRESPONSIVENESS.

PREPARATION FOR LABOUR

CONTRACTIONS ALONG WITH FETAL & PLACENTAL EXPULSION

INVOLUTION

CERVIX SOFTENING RIPENING DILATATION & EFFACEMENT

REPAIR

LABOURIt is the third phase of parturition, comprising

three stages:First stage: from onset of labour pains till

cervix is fully dilated. Second stage of labour: from complete

dilatation of cervix till the delivery.

Third stage of labour: placental separation &expulsion

FIRST STAGE OF LABOUR

Following are the major events during labour: Gradually increasing uterine contractions Retraction Dilatation of cervix Effacement of cervix Lower uterine segment formation

UTERINE CONTRACTIONS IN LABOURCharacteristics of normal uterine contractions: Pace maker: situated in the region of tubal ostia from

where wave of contraction spread downwards. Sometimes there is emergence of multiple pace maker foci

leading to less efficient contractions and hence causing primary dysfunction labour

Fundal dominance with gradual diminishing contractions towards the lower segment.

Polarity of uterus : when upper segment contracts, retracts and pushes the fetus down the lower uterine segment and cervix dilates in response.

Lack of fundal dominance and the reverse polarity leads to spastic lower uterine segment. Here pacemaker does not work in rhythm.

Good synchronization of contraction waves from both sides of uterus.

Regular pattern of contractionsGood relaxation in between the

contractionsIntra amniotic pressure during relaxation

is 8mm rising beyond 20mm during contraction

INTENSITY: describes degree of uterine systole. increases with progress of labour.Maximum during

2nd stage of labourDURATION: initially last for 10-15 seconds gradually

increases up to 40-45 sec.FREQUENCY: in the early stage of labour,

contractions come at the interval of 10-15min and increases to maximum in 2nd stage of labour.

Clinically contractions are said to be good when they come after interval of 3-5minutes and at the height of contractions uterine wall can not be indented by fingers.

TONUS : intra uterine pressure in between the contractions.

During Quiscent stage- 2-3mm Hg During first stage of labour 8-10mmHg.Factors governing tonus are: Contractility of uterine muscles Intra abdominal pressure Over distension of uterus as in twins and

hydramnios.

If the intensity diminishes, duration is shortened and period between the increases it leads to hypotonic uterine dysfunction. Here intrauterine pressure during the contractions remains below 25mm of Hg.

if there is increased frequency and duration without adequate relaxation in between it leads to inco-ordinate uterine action.

It comprises a rise in the base line tone which and hence diminishing the circulation in the intervillous space of placenta

LABOUR PAINSPain during contractions is along the cutaneous

nerve distribution of T10 to L1

Pain of cervical dilatation is radiated to back through sacral plexus

Causes of pain:Myometrial hypoxiaStreching of peritonium over the fundusStreching of cervix during dilatationCompression of nerve ganglia

Retraction Permanent shortening of uterine muscle.net effects are :Formation of lower uterine segment.Maintain advancement of presenting part made

during contractionsReduce the surface area of uterus and hence

favouring placental separation.Effective haemostasis after separation of

placenta.

FRIEDMAN graph of cervical dilation

Latent phase : during which there is little dilatation occurs with considerable changes taking place in the connective tissue component of cervix which include:

Breaking down of collagen by collagease and elastases.

Accumulation of fluid between collagen fibres.Fibro- muscular glandular hypertrophy.Increased vascularity Acceleration phase with cervical dilatation 2.5-4 cm.Phase of maximum slope: between 4-9cmPhase of decelaration: 9-10cm

Caused by:(a)Uterine contraction and retraction:

bucket handle manner of attachment of longitudinal muscle fibres of upper uterine segment with circular muscle fibres of lower uterine segment and cervix. Thus during contraction of upper segment the canal- shortens, retracts and opens.

(b)Bag of membranes : during labour the membranes attached to the lower uterine segment are detached

herniation of membranes through the cervical canal due to ball valve action of well flexed head, during

uterine contraction hydrostaic pressure in forewaters increases

cervical dilatation

Fetal axis pressure: contractions of circular muscles of body of uterus

Straightening of vertebral column of fetus Fundal contractions transmit through podalic

pole in to fetal axis

Mechanical streching of lower uterine segment and opening of cervical canal

Effacement of cervixMuscular Fibres of cervix are pulled upwards and

merge with lower uterine segment. Effacement precedes the dilatation in

primegravidaeWhile it occurs simultaneously with dilatation in

multiparae

Lower uterine segment formationDuring labour lower uterine segment is

demarcated by physiological retraction ring above and fibromuscular junction of cervix and uterus below.

formed maximally during labour.7.5-10 cm when fully formed and cylindrical during

2nd stage of labourPoor retractile property as compared to upper

uterine segment. gradual thinning of lower uterine segment due to

relaxation of its muscle fibres to allow elongation and descent of presenting part

1)implantation of placenta of in lower uterine segment leads to placenta praevia.

2)poor decidual reaction in this segment facilitates morbid adherent placenta.

3)lower segment is entirely the passive segment of uterus. Because of poor retractile property,there is chance of post partum haemorrhage if placenta is implanted over the area.

Uterine tetany: when there is no physiological differentiation between upper active and lower passive segment of uterus whole of the uterus goes in to a tonic muscular spasm holding the fetus inside.

Poor decidual reaction in this segments facilitates morbid adherent placenta if implanted here

Poor retractile property leads to post partum haemorrhage.

SECOND STAGE OF LABOUR It two phases: (a)propulsive: from full dilatation until

head touches the pelvic floor. (b)expulsive: since the time there is

irresistible maternal desire to bear down until the baby is delivered .

Factors leading to expulsion of fetus from uterine

cavity are : Reduced volume due to escape of large amount of

amniotic fluid.Elongation of uterus due to contraction of circular

muscle fibers keeping the fetal axis straight. Reduced transverse or anterioposterior diameter.Downward thurst offered by uterine contractions

supplimented by voluntary contractions of abdominal muscle.

Retraction of uterus which counterbalance the resistance offered by pelvic floor.

Third stage of labour

It comprises expulsion of placenta with membranes

SEPERATION OF PLACENTA: due to shearing force instituted between the placenta and placental site due to marked reduction in the surface area in the placental site and inelasticity of placenta.

PLANE OF SEPERATION: runs through spongy layer of decidua basalis.

METHODS OF SEPERATION : Marginal separation Of Placenta(Mathew

Duncan): more frequent . Separation starts at the margins as it is mostly unsupported.

Central separation (Schultze): detachment starts at centre with opening of few uterine sinuses and collection of retroplacental haematoma. Gradually due to weight of placenta and retroplacental blood collection more and more placenta separates.

SEPARATION OF MEMBRANES: The membranes in the upper part are thrown in to folds while those in the lower part are already detached due to stretching.

Expulsion of placenta : After complete separation the placenta is forced in to the lower uterine segment and then in the vagina.

Complete expulsion occures due bearing down efforts of by manual procedure.

HAEMOSTASISLiving ligature : as the arterioles pass

tortuously through interlacing intermediate layers of myometrium they are actually clamped during uterine contractions.

Thrombosis: occlude torn sinuses as pregnancy is hypercoagulation state.

Myotamponade: apposition of walls of uterus after expulsion of placenta.

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