Normal Labor in Obstetrics

Pathophysiology of Normal Labor:
A series of events that take place in female genital organs to expel the product of conception that are fetus, placenta, membranes) out of womb through the vagina into the outer world. We further describe pathogenesis and features of different stages of labor

1. Pathophysiology of Normal Labor Presented by: Anish Dhakal (Aryan)

2. DEFINITION A series of events that take place in female genital organs to expel the product of conception that are fetus, placenta, membranes) out of womb through the vagina into the outer world. At the National Maternity Hospital in Dublin ( O’Driscoll and colleagues, 1984). Criteria for onset of labor : at term require painful uterine contractions accompanied by any one of the following: ( 1) ruptured membranes, (2) bloody “show ,” or (3) complete cervical effacement.

3. NORMAL LABOR/ EUTOCIA spontaneous in onset and at term with vertex presentation without undue prolongation Natural termination without minimal aid without having any complications affecting the health of the mother and/or the baby

4. Causes of onset of labour Uterine distension Fetoplacental contribution activation of fetal hypothalamic pituitary axis Increase CRT Increase ACTH Fetal adrenals Increase cortisol secretion Accelerated production of oestrogen and PG from the placenta

5. Oestrogen Increases release of oxytocin from maternal pituitary Promotes synthesis of myometrial receptors for oxytocin , prostaglandin. Stimulates synthesis of myometrial contraction protein Increases excitability of myometrial cell Progesterone: Alteration of oestrogen and progesterone ratio is associated with PG synthesis.

6. Prostaglandin Major site of production: Amnion,chorion, decidual cells and myometrium Triggered by rise in estrogen, glucocorticoids, mechanical stretching in late pregnancy, separation or rupture of membrane Enhances gap junction formation Oxytocin Actions Stimulate uterine contractions Stimulate PG production from amnion/ decidua

7. TRUE AND FALSE LABOR True labor Uterine contractions at regular intervals Contraction frequency, intensity, duration increases gradually Associated with show Progressive effacement and dilatation of cervix Descent of presenting part Formation of “bags of water” Not relieved by enema/ sedative False labor Dull pain confined to groin and abdomen Pain interval doesn’t shorten Pain intensity remains same No cervical dilatation No hardening of uterus Relieved by enema or sedative

8. Physiology of normal labour Marked hypertrophy and hyperplasia of uterine muscles Length of uterus + cervix = 35 cm at term Uterus assumes pyriform/ ovoid shape Cervical canal occluded by thick, tenacious mucus plug

9. PATTERN OF CONTRACTION Good synchronization of contraction waves from both halves of the uterus Fundal dominance Regular wave of contraction Intra-amniotic pressure rises beyond 20mm Hg during uterine contraction Good relaxation occurs in between contraction

10. RETRACTION Phenomenon of uterus in labor in which muscle fibers are permanently shortened Effects of retraction: Formation of lower uterine segment and dilatation and effacement of cervix Decent of presenting part  expulsion of fetus Reduce surface area  separation of placenta Effective homeostasis after separation of placenta

11. STAGES OF LABOR First phase Second phase Propulsive Expulsive Third phase Fourth phase

12. FIRST STAGE Concerned with formation of birth canal Main events: Dilatation of cervix and effacement of cervix Lower uterine segment formation

13. FACTORS RESPONSIBLE IN DILATATION Uterine contraction and retraction

14. FACTORS RESPONSIBLE IN DILATATION Fetal axis pressure longitudinal lie of fetus  circular muscles contraction Fundal contraction to transmit from podalic pole to head Bag of membrane Vis-a- tergo

15. EFFACEMENT OF CERVIX Muscular fibers of cervix pulled upward and merge with fibers of lower uterine segment Primigravidae: effacement before dilation of cervix Multiparae: effacement and dilatation occur at same time

16. Latent Phase 3 to 5 cm of dilation After that clinically active labor can be expected Prolonged latent phase: > 20 hours in nullipara and 14 hours in multipara (Friedman and Sachtleben ) Following heavy sedation: 85 percent to active labor 10 percent uterine contraction ceased 5 % persisted: require oxytocin stimulation

17. Williams Obstetrics 24 th edition page.: 446

18. Active Phase Cervical dilation of 3 to 5 cm in presence of uterine contractions: threshold for active labor Cervical dilatation: 1.2 to 6.8 cm/hour. Multiparas: minimum 1.5 cm/hr Descent begins after 7 to 8 cm dilation, most rapid after 8 cm

19. Williams Obstetrics 24 th edition page.: 445

20. SECOND STAGE OF LABOR Begins when cervical dilatation is complete and ends with fetal delivery. Median duration 2 hr in primigravidae 30 minutes in multiparae Uterine contractions and accompanying expulsive forces last: 60-90 seconds and recur every 60 seconds

21. Events Propulsive phase: Period of full dilation until head touches pelvic floor Expulsive phase: Since the time mother has irresistible desire to ‘bear down’ and push until the baby is delivered

22. THIRD STAGE OF LABOR Includes separation, descent and expulsion of placenta with its membrane.

23. Types of placental separation

24. Signs of placental separation: The uterus becomes globular and as a rule, firm- woody Sudden gush of blood Uterus rises in abdomen because the placenta, having separated, passes down in the lower uterine segment and vagina. Umbilical cord protrudes farther out of the vagina, indicating that the placenta has descended.

25. FOURTH STAGE OF LABOR The placenta, membranes and umbilical cord should be examined for completeness and for anomalies Laceration of birth canal(vagina and perineum): First degree laceration : Involved the perineal skin, vaginal mucus membrane but not underlying fascia and muscle 2 nd degree laceration : Involve in addition, the fascia and muscle of perineal body but not anal sphincter 3 rd degree laceration : Extent further to involve the anal sphincter 4 th degree laceration : Laceration extend through the rectum’s mucosa to exposed its lumen

26. MANAGEMENT OF FIRST STAGE LABOR Rest and ambulation Oral intake Urinary bladder function Bladder distention-avoided, because it can hinder descent of the fetal presenting parts Pain relief Monitoring fetal well-being during labor Uterine contractions to evaluate the frequency, duration, and intensity of uterine contractions.

27. CONTD.. 8. Maternal vital signs Maternal temperature, pulse, and blood pressure are evaluated at least every 4 hours with prolonged membrane rupture(>18 hours) antimicrobial administration for prevention of group B streptococcal infections is recommended 9. Subsequent vaginal examinations 10.Maternal position position that she finds most comfortable, which will be lateral recumbency most of the time

28. Management of second stage labor Assist in natural expulsion of fetus slowly and steadily Prevent perineal injuries 1. Preparation for delivery Put the patient in dorsal lithotomy position or lying flat on bed Clean the vulva, and perineum with antiseptic solution Clean hands, Clean surface, Clean cutting and ligaturing of the cord Catheterize the bladder, if full

29. 2. Conduction of delivery Delivery of head : Maintain flexion of the head Prevent early extension Regulate the escape out of vulval outlet

30. Patient asked for bearing down efforts during uterine contractions When the scalp is visible for about 5cm in diameter, push occiput downward and backwards using thumb and index fingers while pressing the perineum by right hand with sterile vulval pad BPD stretches the vulval outlet without any recession of the head even after the contraction is over

31. With each contraction, perineum bulge increasing Slow delivery of the head in between the contractions Ritgen maneuver: A towel-draped ,gloved hand –used to exert forward pressure on the chin of fetus through the perineum This maneuver allow delivery of head and also favors the neck extension so that head is delivered with small diameter

32. Management of third stage labor Expectant management Placental separation and its descent into the vagina are allowed to occur spontaneously Constant watch Changed to dorsal position Hand placed over the fundus (signs of separation, state of uterine activity, detect inversion of uterus) Expulsion of placenta Patient asked to bear down Placenta grasped by hands and twisted round and round with gentle traction

33. Assisted expulsion 1. Controlled Cord Traction 2.Fundal Pressure

34. Examination of placenta Maternal surface: completeness, anomalies Membranes: completeness, abnormal vessels Cord: number of vessels

35. Active management To excite powerful uterine contractions within one minute of delivery of the baby by giving parenteral oxytocic Injection Oxytocin 10 units IM Controlled Cord Traction Massaging the uterus To minimise blood loss in third stage to approx 1/5 th To shorten the duration of third stage to half Disadvantage: increased incidence of retained placenta and consequent increased incidence of manual removal Not to be used in cardiac failure, severe pre- eclampsia

36. Management of fourth stage labor Suture the episiotomy or any laceration Estimate blood loss, take cord blood for Hb , blood group, Rh , bilirubin, and Coomb’s test for Rh negative mother Check BP, Pulse, Temperature, abnormal vaginal bleeding and firmness of the uterus before transferring the patient

37. Cardinal Movements of Labor Engagement Descent Flexion Internal rotation Extension External rotation Expulsion

38. Engagement The mechanism by which the Biparietal Diameter- the greatest transverse diameter in occiput presentation crosses the pelvic inlet. Fetal head enters the pelvic inlet either transversely or obliquely. 1. Head floating before engagement 2. Engagement, descent and flexion

39. Asynclitism The lateral deflection of the sagital suture anteriorly toward pubic symphysis or posteriorly towards sacral promontory. Anterior asynclitism : Sagital suture approaches sacral promontory Anterior parietal presentation Posterior asynclitism : Sagital suture approaches pubic symphysis Posterior parietal presentation

40. Descent Downward passage of the presenting part through the pelvis Forces involved:- Pressure of amniotic fluid Pressure of fundus upon breech with contraction Bearing down efforts of maternal abdominal muscles Extension and straightening of fetal body

41. Flexion Occurs passively as the head descends Resistance from cervix, pelvic walls, pelvic floor Chin is brought into intimate contact with the fetal thorax Longer occipitofrontal diameter replaced by shorter suboccipito bregmatic diameter 2. Engagement, descent and flexion

42. Internal Rotation Turning of head in such a manner that the occiput gradually moves towards the symphysis pubis anteriorly from its original position. 3. Further descent and beginning of internal rotation 4. Completion of internal rotation

43. Extension The sharply flexed head reaches the vulva and undergoes extension Driving force exerted by uterus Resistance offered by pelvic floor and symphysis Resultant vector: direction of vulvar opening causing head extension Occiput in direct contact with the inferior margin of symphysis pubis

44. External Rotation Movement of rotation of head visible externally due to the internal rotation of the shoulders Anterior shoulder rotates towards symphysis pubis from oblique diameter Occiput points directly toward maternal thigh corresponding to the side to which it originally directed at the time of engagement.

45. Expulsion Shoulders positioned in anteroposterior diameter Anterior shoulder escapes below pubic symphysis Lateral flexion of spine, the posterior shoulder sweeps over the perineum Rest of the trunk expelled out by lateral flexion 7. Delivery of anterior shoulder

46. Reference Williams Obstetrics 24 th edition D.C. Dutta, Textbook of Obstetrics, 9 th Edition