Events in First Stage of Labour

 Events in first stage of labor

Start with true labour pain and full dilatation of cervix.

1. Dilatation and effacement of cervix

2. Full formation of lower uterine segment 

First stage of labor events

1. Latent phase

(0-3 cm)

Begin with regular contraction (true labour pain)

Every 5 minutes (25-35 second (

2. Active phase

(4-7cm)

More active contraction

Contraction frequent 

Every 3-5 minutes (60 second)

Moderate to strong intensity

Cervical dilatation 

In primi; 1 cm/hr

In multi; 1.5cm/hr

Phase of Active labour

1. Acceleration phase

2. Maximum slope

3. Deaccleration phase

3. Transitional phase

(7-10cm)

Intense phase of labour

Strong contraction

More frequent

More intensity

Every 2 to 3 minutes ( 60-90 seconds)

Rectal pressure

Bearing down efforts

Increase bloody show

Spontaneous repture of membrane

1. Fetal axis pressure

In longitudinal lie of fetus, due to mechanical stretching, fundal contraction, straightening of fetal vertebral column pressure created on cervix hence dilate.

But in transverse lie absent.

2. Dilatation of cervix

Softening of cervix

Fibro-musculo-glandular hypertrophy

Increase vascularity

Accumulation of fluid in between collagen fibres

Breakdown of collagen fibrils by enzyme collagenase and elastase

Change in various glycosaminoglycans (for examples; increase in hyaluronic acid, decrease in dermatan sulphate)

These action due to action of hormones; oestrogen, progesterone and relaxin.

Relaxin hormone loosens and relax the muscles, joints and ligaments during pregnancy to help body stretch.

3. Uterine contraction and Retraction

Uterine contraction; tightening of uterine muscles

Retraction; shortening muscles fibres

4. Bag of membrane

Hind water

Fore water

5. Effacement of cervix

Thinning of cervix and taking up of cervix 

6. Expulsion of muscus plug caused by effacement

7. Vis-a-tergo

Downward push of presenting part of fetus. Upward pull of cervix over lower segment.

8. Formation of upper and lower segment

Retraction ring; line between upper and lower uterine segment present during normal labour.

9. Cervical dilatation or cervical ripening

Refers thinning of cervix.

1. Cervix is not effaced or dilated

2. Cervix is 50% effaced or dilated

3. Cervix is 100% effeced and dilated to 3cm

4. Cervix is fully dilated to 10cm