Extra information about stage 1 of labour

Question 1

Contractions and retraction of the myometrium

Answer 1

• Occurs involuntarily under nervous and hormonal control
• commences in these funds near the cornua (top corners of uterus)
• spread in a wave across the fundus and down the the body of the uterus

Question 2

Fundal dominance

Answer 2

Contractions are stronger and last longer in the upper part of the uterus
They are considerably weaker in the lower part of the uterus

Question 3

Contraction pattern of stage 1

Answer 3

• Contractions increase in length strength and frequency as labour progresses
• Circulation of blood through the uterine wall to the placental bed is obstructed during contractions

Question 4

What happens during a contraction?

Answer 4

-Begins painless
-Increases to a peak
- Ends painlessly
Resting tone of uterus = 10mmHg
Pain is felt at =20-25mmHg
Peak of strong contraction =50-60mmHg
Contractions should increase in:
-length (30-40-60secs)
-strength ( weak/mod/strong)
-frequency (1:10/ 1:5/1:2)

Question 5

What happens during the retraction of the uterus?

Answer 5

Unique to the myometrium

• Muscle fibres retain some of each contraction instead of relaxing completely
• result- muscle fibres become shorter and thicker

Question 6

Functional division of the uterus into upper and lower segments.
Upper uterine segment (UUS)

Answer 6

• This is an active process
• Longitudinal fibres (outer layer of the myometrium) are contracted
• Contraction and retraction of fibres cause the UUS to thicken from 6-25mm by the end of the first stage.
• cavity of the uterus decreases
• foetus descends into the birth canal.

Question 7

Functional division of the uterus into upper and lower segments
Lower uterine segment LUS

Answer 7

• This is a passive process
• Circular fibres (the inner layer of the myometrium) are in the LUS
• Circular fibres only contract slightly
• They are stretched and thinned

Question 8

What is the retraction ring?

Answer 8

A ridge that forms between the thickening UUS and the thinning LUS

Question 9

What is polarity?

Answer 9

The term given to the neuro muscular harmony between the UUS and the LUS

Question 10

What is effacement?

Answer 10

‘Taking up’ of the cervix into the lower uterine segment.

• In a primipara effacement starts at the end of pregnancy once the presenting part has engaged and before dilation begins
• in a multipara effacement and dilation occur together.

Question 11

What is effacement and dilation of the cervix caused by?

Answer 11

Combined effects of:

• contraction and retraction, fundal dominance and polarity
• pressure on the presenting part of the cervix.

Question 12

What is feral axis pressure?

Answer 12

During a contraction the force of th fundal contraction is transmitted to the upper pole of the foetus (normally its bum)
And down its long axis (spine)
Until the presenting part is applied to the cervix
This results in flexion of the foetus

Question 13

What is ‘the show’?

Answer 13

As effacement and dilation progress the cervical mucous plug is shed

Question 14

Mechanical factors in the first stage of labour

Formation of fore waters and hind waters

Answer 14

As the cervix dilates and the LUS stretches the chorion becomes detached from the decidua in the surrounding area.
- Small bag of membranes forms
- As the Presenting part defends the liquor is decided into the fore waters and hind waters
Forewaters- the liquor inform of the PP
Hind waters- the liquor behind the PP