This document discusses normal uterine action during labor, which comprises 4 stages: 1) cervical dilation, 2) delivery of the baby, 3) placental separation and expulsion, and 4) the first hour after delivery. It describes the major events during labor like increasing contractions, cervical effacement and dilation. Contraction characteristics like frequency, duration, intensity, and resting tone are defined. Abnormal uterine contractions can cause ineffective labor and are classified as coordinated issues like hyperfunction or hypofunction, or incoordinated issues like a colicky or tonic uterus.

1. Normal Uterine Action
Ayman Shehata
Ass.Lect. Ob/Gyn

2. LABOUR
comprising 4 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
Fourth stage : first hour after delivery

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

5. Duration:
o primigravida = 8-12 h
o multigravida = 6-8 h
Phases of the first stage:
 Latent phase: started when the cervix dilatated
slowly and reached to about 3cm.
A. in primigravida = 8h
B. in multigravida = 4h
 - Active phase: rapid dilatation of the cervix to
reach 10cm
A. in primigravda = 4h
B. in multigravida =2h

6. UTERINE CONTRACTIONS
 FUNDAL DOMINANCE
 POLARITY
 COORDINATION
 EFFECTIVENESS
 FREQUENCY
 DURATION
 INTENSITY
 INTERVAL
 RESTING TONE(TONUS)

7. Fundal dominance
 Fundal dominance
The activity of myometrium is greatest &
longest at the fundus, shifting &diminishing
towards midline and downwards ( towards
cervix)

8.  Pace maker
 Two one at each cornu from where wave of
contraction spread downwards.
 Their activities must be coordinated
 Propagation of wave must also be
coordinated
Sometimes there is emergence of multiple
pace maker foci leading to less efficient
contractions and hence causing primary
dysfunction labour

9. Polarity of uterus
 When upper segment contract the lower
segment relaxes.

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

12. Coordination
 Wave begins earlier in some part than
other but the contraction attains maximum
in the different parts of uterus at the same
time.
 At peak of contraction entire uterus acts as
a single unit.
 Relaxation Starts simultaneously in all parts
of uterus.
 For normal uterine action coordination is
required between both halves of uterus as
well as between upper and lower segments

13. UTERINE CONTRACTIONS
 FUNDAL DOMINANCE
 POLARITY
 COORDINATION
 EFFECTIVNESS
 FREQUENCY
 DURATION
 INTENSITY
 INTERVAL
 RESTING TONE(TONUS)

14. EFFECTIVNESS
 The effective uterine contractions results
progressive cx dilatation & descent of head
within a given time. Any deviation of normal
pattern of uterine contraction that affects
the course of labour is known as abnormal
uterine action

15. FREQUENCY
 Frequency- the amount of time between the start of one
contraction to the start of the next contraction.
 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.

16. FHR and Uterine Activity

17. DURATION
 Duration- the amount of time from the start of a
contraction to the end of the same contraction.
 Normal labour is characterised by minimum
of three contractions that averaged >25
mmHg in 10 minutes lasting for certain
duration
<20 sec: mild,
20-40 sec: mod
> 40 sec: strong

18. FHR and Uterine Activity

19. Intensity or Amplitude
Intensity- a measure the strength a contraction
by measuring the rise in intrauterine pressure
brought about by each contraction. Measured
from baseline resting tonus
 With external monitoring, this necessitates
the use of palpation to determine relative
strength.
 With an IUPC, this is determined by assessing
actual pressures as graphed on the paper.

24. TONUS (Resting tone)
 TONUS : intra uterine pressure in between the
contractions.
 With external monitoring, this necessitates the use
of palpation to determine relative strength.
 With an IUPC, this is determined by assessing
actual pressures as graphed on the paper
 During Quiscent stage- 2-3mm Hg
 During first stage of labour 8-10mmHg.

26. Uterine Tone
 The lowest intrauterine pressure between
contractions is called resting tone
 Normal resting tone is 5-10 mmHg; during
labor resting tone may rise to 10-15 mmHg
 Pressure during contractions rises to ~25-100
mmHg (varies with stage)
 A resting pressure above 20 mmHg causes
decreased uterine perfusion

27. INTERVAL
 Interval- the amount of time between the end
of one contraction to the beginning of the
next contraction.

28. FHR and Uterine Activity

29. Uterine Activity
 Uterine activity can be quantified the number
of contractions present in a 10-minute
window, averaged over 30 minutes. Uterine
activity may be defined as:
 Normal- less than or equal to 5 contractions
in 10 minutes, averaged over a 30-minute
window
 Tachysystole more than 5 contractions in 10
minutes, averaged over a 30-minute window

30. Assessment of Uterine contractions
- Clinical palpation: by placing hand over
uterus
- Tocodynamometer: with external transducer
measures the duration and frequnecy but
not the stenghth.
– IUPC: assess the strength of uterine
contractions can be measured by
intrauterine pressure catheter.

31. Uterine activity
–Montevideo unit
average intensity of uterine contraction x
frequency
-Alexandria unit
average intensity of uterine contraction in mm
of Hg x frequency / 10 min x average
duration contraction in minutes

32. Uterine Contractions

33. Uterine contraction:
 Uterine cont. has three phases:
 Increment: building up of the contraction
 Acme: peak or highest intensity
 Decrement: descent or relaxation of the
uterine muscle fibers

35. Uterine contraction during pregnancy
Less than 30 weeks
–frequency and strength of contraction low
i.e.<20 Montevideo units
After 30 weeks
-contractions are more frequent and may be
noticeable by patient. When painful

36. Classifications of AUA
□Coordinated uterine action
 Hyperfunction
 Precipitate labour: in absence of obstruction
 Pathological retraction ring: Excessive contraction and
retraction in presence of obstruction
 Hypofunction
 Hypotonic inertia (1ry and 2ry)
 Cervical dystocia (1ry and 2ry)
□Incoordinated uterine action
 Colicky uterus
 Tonic uterus
 Hyperactive lower uterine segment
 Constriction (contraction) ring

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