Normal uterine action

Normal Uterine Action

Ayman Shehata

Ass.Lect. Ob/Gyn

LABOURcomprising 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

Following are the major events during labour:

Gradually increasing uterine contractions

Retraction

Dilatation of cervix

Effacement of cervix

Lower uterine segment formation

Duration:

o primigravida = 8-12 h

o multigravida = 6-8 h

Phases of the first stage:

Latent phase: started when the cervix dilatatedslowly 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

UTERINE CONTRACTIONS

FUNDAL DOMINANCE

POLARITY

COORDINATION

EFFECTIVENESS

FREQUENCY

DURATION

INTENSITY

INTERVAL

RESTING TONE(TONUS)

Fundal dominance

Fundal dominance

The activity of myometrium is greatest &

longest at the fundus, shifting &diminishing

towards midline and downwards ( towards

cervix)

Pace maker

Two one at each cornu from where wave ofcontraction spread downwards.

Their activities must be coordinated

Propagation of wave must also be coordinated

Sometimes there is emergence of multiplepace maker foci leading to less efficientcontractions and hence causing primarydysfunction labour

Polarity of uterus

When upper segment contract the lower

segment relaxes.

Lack of fundal dominance and the reverse

polarity leads to spastic lower uterine segment.

Here pacemaker does not work in rhythm.

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

UTERINE CONTRACTIONS FUNDAL DOMINANCE

POLARITY

COORDINATION

EFFECTIVNESS

FREQUENCY

DURATION

INTENSITY

INTERVAL

RESTING TONE(TONUS)

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

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.

FHR and Uterine Activity

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

FHR and Uterine Activity

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 necessitatesthe use of palpation to determine relativestrength.

With an IUPC, this is determined by assessingactual pressures as graphed on the paper.

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.

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

INTERVAL

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

FHR and Uterine Activity

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

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.

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

Uterine Contractions

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

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

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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