PHYSIOLOGY OF NORMAL LABOUR

1. PHYSIOLOGY OF NORMAL LABOUR DR. POOJA RAJBHARA SENIOR RESIDENT

2. 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 phase, • Stimulation phase, • Involution phase.

6. LABOUR • It is the third phase of parturition, comprising three stages; • First Stage : - From onset of labour pains till cervix is fully dilated. • Second Stage : - From complete dilatation of cervix till the delivery. • Third Stage :- Placental separation & expulsion.

8. 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

9. UTERINE CONTRACTIONS IN LABOUR Characteristics 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 dominancewith 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 dilats in response. Lack of fundal dominance and the reverse polarity leads to spastic lower uterine segment. Here pacemaker does not work in rhythm.

10. UTERINE CONTRACTIONS IN LABOUR ….CONT. • Good synchronization of contraction waves from both sides of uterus. • Regular pattern of contractions • Good relaxation in between the contractions • Intra amniotic pressure during relaxation is 8mm rising beyond 20mm during contraction

11. INTENSITY : Describes degree of uterine systole. Increases with progress of labour. Maximum during 2nd stage of labour • DURATION : initially last for 10-15 seconds gradually increases upto 40-45 sec. • FREQUENCY : in the early stage of labour, contractions come at the interval of 10-15 min and increases to maximum in 2nd stage of labour. Clinically contractions are said to be good when they come after interval of 3-5 minutes and at the height of contractions uterine wall can not be indented by fingers.

12. TONUS : intra uterine pressure in between the contractions. • During Quiscent stage- 2-3 mm Hg, • During first stage of labour 8-10 mm Hg. • Factors governing tonus are; • Contractility of uterine muscles, • Intra abdominal pressure, • Over distension of uterus as in twins and hydramnions.

13. If the intensity diminishes, duration is shortened and period between the contraction 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 contractions it leads to incordinate uterine action. It comprises a rise in the base line tone and hence diminishing the circulation in the intervillous space of placenta.

14. LABOUR PAINS Pain 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 hypoxia, • Stretching of peritonium over the fundus, • Stretching of cervix during dilatation, • Compression of nerve ganglia

15. Retraction • Permanent shortening of uterine muscle. • net effects are : • Formation of lower uterine segment. • Maintain advancement of presenting part made during contractions. • Reduce the surface are of uterus and hence favouring placental separation. • Effective heamostasis after separation of placenta.

17. Latent phase : during which there little dilatation occurs with considerable changes taking place in the connective tissue component of cervix which include; • Breaking down of collagen by collagenase and elastases. • Accumulation of fluid between collagen fibers. • Fibro-muscular glandular hypertrophy. • Increased vascularity Acceleration Phase with cervical dilatation 2.5-4 cm. Phase of maximum slope : between 4-6 cm. Phase of decelaration: 9-10 cm

19. Caused by : (a) Uterine contraction and retraction : bucket handle manner of attachment of longitudinal muscle fibers of upper uterine segment with circular muscle fibers of lower uterine segment and cervix. Thus during contraction of upper segment the canal-shortens, retracts and opens.

21. (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 hydrostatic pressure in forewaters increases. cervical dilatation

23. 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 stretching of lower uterine segment and opening of cervical canal.

24. Effacement of cervix • Muscular Fibers of cervix are pulled upwards and merge with lower uterine segment. • Effacement precedes the dilatation in primegravidae • While it occurs simultaneously with dilatation in multiparae

26. Lower uterine segment formation • During 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 labour. • Poor 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.

27. Lower uterine segment formation….Con. • Implantation of placenta of in lower uterine segment leads to placenta praevia. • Poor decidual reaction in this segment facilitates morbid adherent placenta. • 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.

30. 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.

31. SECOND STAGE OF LABOUR • It two phases : • Propulsive : from full dilatation until head touches the pelvic floor. • Expulsive : since the time there is irresistible maternal desire to bear down until the baby is delivered.

32. 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 thurstoffered by uterine contractions supplemented by voluntary contractions of abdominal muscle. • Retraction of uterus which counterbalance the resistance offered by pelvic floor.

34. THIRD STAGE OF LABOUR It comprises expulsion of placenta with membranes. SEPARATION 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 SEPARATION : runs through spongy layer of decidua basalis.

36. METHODS OF SEPARATION : - • 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 retroplacentalhaematoma. Gradually due to weight of placenta and retroplacental blood collection more and more placenta separates.

38. 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 occurs due bearing down efforts or by manual procedure.

39. HARMOSTASIS • Living 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 hyper coagulation state. • Myotamponade : apposition of walls of uterus after expulsion of placenta.

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