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
o Stimulate uterine contractions
o Stimulate PG production from amnion/decidua

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

9. 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

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

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

12. STAGES OF LABOR
 First phase
 Second phase
 Propulsive
 Expulsive
 Third phase
 Fourth phase

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

14. FACTORS RESPONSIBLE IN
DILATATION
 Uterine contraction and retraction

15. 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

16. 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

17. 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:
1. 85 percent to active labor
2. 10 percent uterine contraction ceased
3. 5 % persisted: require oxytocin stimulation

18. Williams Obstetrics 24th edition page.: 446

19. 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

20. Williams Obstetrics 24th edition page.: 445

21. 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

22. 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

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

24. Types of placental
separation

25.  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.

26. 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
 2nd degree laceration: Involve in addition, the fascia and muscle of
perineal body but not anal sphincter
 3rd degree laceration: Extent further to involve the anal sphincter
 4th degree laceration: Laceration extend through the rectum’s
mucosa to exposed its lumen

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

28. 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

29. 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

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

31. • 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

32. • 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

34. 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

35. • Assisted expulsion
1. Controlled Cord Traction 2.Fundal Pressure

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

37.  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 1/5th
• 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

39. 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

40. Cardinal Movements of
Labor
1. Engagement
2. Descent
3. Flexion
4. Internal rotation
5. Extension
6. External rotation
7. Expulsion

41. 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

42.  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

43. 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

44. 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

45. 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

46. 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

47. 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.

48. 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

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