Physiology and causes of labour

LABOUR UNIT 4

1. Physiology of normal labour

2. Labour Labour : Series of events that take place in the genital organs in an effort to expel the viable products of conception out of the womb through the vagina into the outer world is called labour .

3. Normal Labour : (EUTOCIA) Labour is called normal, if it ful fills the following criteria Spontaneous in onset & at term. With vertex presentation Without undue prolongation Natural Termination with minimal Aids Without having any complication affecting the health of the mother and/ or baby. Abnormal Labour : Any deviation from the definition of normal labor is called abnormal labour i.e. the condition that adversely affecting the maternal and/or fetal prognosis is called abnormal labour .

4. Causes: Uterine distention:

5. Oestogen – probable causes are Increases the release of oxytocin from maternal pituitary Promotes the synthesis of receptors for oxytocin in the myometrium and decidua Accerlates lysosomal disintegration in amnion cells resulting in increased prostaglandin synthesis Stimulates the synthesis of myometrial contactile protein – actomycin thro’ camp Increases the excitability of the myometrial cell membranes

6. Progesterone Increased fetal production of DHEA-S and cotisol Inhibits the conversion of feto - pregnenolene to progesterone Progesterone levels therefore fall before labour Alteration in the oestrogen:progesterone ratio rather than the fall in the absolute concentration of progesterone which is linked with prostaglandin synthesis

7. Prostaglandins Prostaglandins are the important factors which initiate and maintain labour . The major sites of synthesis of porstaglandin are- amnion, chorion , decidual cells and myometrium . Synthesis is triggered by Rise in estrogen level, glucocoticoids , mechanical stretching in late pregnancy, increase in cytokines, infection, sepration or rupture of the membranes

8. Oxytocin There is oxytocin receptors in the uterus Oxytocin receptors are increased in the uterus with the onset of labour Oxytocin promotes the the release of prostaglandins from the decidua Oxytocin synthesis is increased in the decidua and in the placenta

9. Neuroiogical factor: Although , labour may start in denervated uterus, labour may also be initated through nerve pathway. Both alpha & beta adrenergic receptors are present in the myometrium ; estrogen causing the alpha receptors and progesterone causing the beta receptors to function predominantly.

10. FALSE PAIN: (spurious labour ) It is found more in primigravida than in parous women. It is usually appears prior to the onset of true labour pains, by one or two weeks in primigravidae and by a few days in multipara . Features of false pain: Dull in nature and usually confined to the lower abdomen and groin. Continuous and unrelated with hardening of uterus. Without any effect on dilatation of cervix. Usually relieved by enema & administration of a sedation.

11. PRE LABOUR: (premonitory stage) may begin two to three weeks before the onset of true labour in primigravida and a few days in multipara the features are inconsistent and may consist of the following. Lightening: 2-3 weeks before the onset of labour the lower uterine segment expands and allows the fetal head to sink lower and it may engage in the pelvis, particularly in first time mothers when this happens the fundus of the uterus descends and there is more room for lungs, breathing is easier and the heart and stomach can function more easily . the woman may experience relief. There may be frequency of micturition or constipation due to mechanical factor-pressure by the engaged presenting part. It is a “welcome sign”. Cervical changes : prior to the onset of labour cervix becomes ripe. A ripe cervix is soft, less than 1.5 cm in length. Appearance of false pain

12. TRUE LABOUR PAINS: features are: Painful uterine contractions at regular intervals. Contraction with increasing intensity and duration. It occurs as a result of loss of cervical plug “show” and blood from ruptured capillaries of parietal decidua . It is blood stained mucoid discharge. Progressive effacement and dilatation of the cervix. Formation of the “bag of waters”

13. Physiology of labour During pregnancy there is marked hypertrophy and hyperplasia of the uterine muscles and the enlargement of round ligaments. At term length of uterus measures about 35 cm inclunding cervix and the fundus is much wider.

14. UTERINE CONTRACTION IN LABOUR: Throughout pregnancy there is rhythmic invlountary spasmodic uterine contractions which are painless and have no effect on dilatation of cervix, the character of the contractions changes with the onset of labour . The pace maker of the uterine contractions is probably situated in the region of the tubal ostia from where waves of contraction spread downwards.

15. Fundal dominance

16. contractions follow the following patterns There is good synchronization of the contraction waves of both halves of uterus. The waves of contractions follow a regular pattern Intra amniotic pressure rises beyond 20mmhg with the onset of true labour pains during contractions. Good relaxation occur in between contractions to bring down the intra amniotic pressure to less than 8 mmhg . During contraction, uterus becomes hard and some what pushed anteriorly to make the long axis of the uterus in time with that of pelvic axis simulataneously patient experiences pain, often radiating to the thighs.

17. Probable causes of pain are: Myometrial hyoxia during contractions. Stretching of the peritoneum over the fundus . Stretching of the cervix during dilatation. Compression of the nerve ganglion.

18. Tonus: It is the intra uterine pressure in between the contractions During pregnancy, the tonus is of 2-3 mnhg . During first stage of labour , it varies from 8-10mn Hg . It inversely proportional to relaxation.

19. Intensity: The intensity of uterine contraction describes the degree of uterine systole. The intensity gradually increases with advancement of labour while it becomes maximum in second stage during delivery of baby. Intra uterine pressure increases upto 40-50 mnHg during first stage. About 100-120 mnHg in second stage of labour during contractions. Inspite of diminished pain in third stage the intra uterine pressure is probably the same as that in second stage.

20. Duration: In first stage the contractions last for about 30 secs initially but gradually increases in duration with the progress of labour . In second stage contractions last longer than in first stage. Frequency : In the early stage of labour , contraction comes at interval of10-15 mins . In second stage it comes every 2-3 mins . It is important to note that all features of uterine contractions mentioned are very effective only when they are in combination.

21. RETRACTION : Retraction is a phenomenon of the uterus in labour in which muscle fibres are permanently shortend . Uterine muscles have this property to become shortened once and for all. The net effects of retraction in normal labour are: Essential property in the formation of lower uterine segment and dilatation & effacement up of the cervix. To maintain the advancement of the presenting part made by uterine contractions and help in ultimate expulsion of the foetus .

22. Contraction and Retraction