First Stage Of Labour

Question 1

What is the first stage of labour?

Answer 1

The onset of regular uterine contractions accompanied by the effacement of the cervix and dilatation of the os.

Question 2

What are the 3 phases of the first stage of labour (describe them)

Answer 2

Latent phase- cervix dilates from 0-3/4 cm. cervix shortens from 3cm to less than 0.5cm long
Active phase - more rapid dilatation, from 4cm dilation, rhythmic contractions, complete when cervix is fully dilated
Transition- cervix around 8cm until expulsion contractions. Brief lull in intensity of contractions

Question 3

What is spurious/false labour?

Answer 3

Women experience contractions prior to onset of labour
Can be painful
May be regular for a time
No effacement or dilatation of the cervix
No effect of contractions on cervix

Question 4

Why must labour be seen as a continuum?

Answer 4

Labour is a physiological process rather than an event. In physiological terms, pregnancy and labour are part of a continuum and therefore cannot be considered as seperate entities.

Question 5

What physiological changes take place in the first stage?

Answer 5

Cervix undergoes structural changes to support the birth canal
Myometrial tone of the uterus changes to allow coordinate contractions.

Question 6

What causes the onset of spontaneous physiological labour?

Answer 6

Complex interaction of maternal and fetal hormones
Process not fully understood
Onset is multi factorial - hormonal and mechanical

Question 7

What hormonal factors influence the onset of labour?

Answer 7

Increased DHAS production leads to synthesis of placental estradiol (leads to increased oxytocin receptors)
Maternal oestrogen also rises sharply in last few weeks
This causes uterine muscle fibres to display oxytocic receptors
Form gap junctions with each other
Increased ratio of oestrogen and progesterone leads to increased uterine contractility (unclear evidence for this)
Plants releases prostaglandins which produce enzymes to help digest collagen in the cervix

Question 8

What are gap junctions?

Answer 8

Specialised intercellular connection between animal cell types. They directly connect the cytoplasm of two cells which allows various molecules to pass between cells.

Question 9

Mechanical/neurohormonal factors that may causes onset of labour

Answer 9

Uterine activity (Braxton hicks) may result in stimulation of uterus and cervix
Over stretching of uterus
Pressure from presenting part on the cervix

Question 10

Describe cervical effacement

Answer 10

Cervix drawn up and merges into lower segment of uterus
Occurs late in pregnancy or not until labour commences
Primip- complete effacement before dilatation
Multip- effacement and dilatation may occur simultaneously

Muscle fibres surrounding internal os drawn upwards by retracted uterine segment, cervix merges into lower segment or external os taken up first, outward rolling movement, cervix thins from external so upwards

Question 11

Outline other factors to consider in the first stage of labour

Answer 11

Show (operculum) blood stained mucous anything from days to a few hours before or after labour has started. Blood from ruptured capillaries parietal decidua where chorion came detached
Membranes may rupture

Question 12

What is fundal dominance

Answer 12

Each contraction starts in the fundus near one cornua and spreads across and downwards
Contractions lasts longest in the fundus, most intense

Question 13

Describe contractions in the first stage of labour

Answer 13

Every woman very different and individual
At onset every 15-20 minutes last for 30 seconds
Fairly weak may not even be felt by woman
Rhythmic regularity
Intervals between them lessen
Increase through latent phase into active phase
At end of first stage every 2-3 mins powerful t

Question 14

Describe the polarity of the uterus

Answer 14

Neuromuscular harmony between two poles or segments or uterus throughout labour
2 poles act harmoniously
Upper - contract and relax to expel foetus
Lower- contracts slightly, dilates to allow expulsion
Progress is inhibited is polarity is disorganised

Question 15

What is contraction and retraction?

Answer 15

Unique property of uterine muscle
During labour contraction does not fully pass off
Muscle fibres retain some of the shortening instead of completely relaxing
Called retraction

Question 16

Outline the formation the upper and lower segment of the uterus

Answer 16

End of pregnancy the uterus has two segment
Upper - contraction and retraction, thick and muscular
Lower- distension and dilatation
No clear or strict division
Retracted longitudinal fibres in upper segment pulls on lower segment

Question 17

What is the retraction ring?

Answer 17

Ridge between segments (a physiological ring)
Rises up as upper uterine segment contracts and retracts
Rises no further once cervix is fully dilated and fetus can leave he uterus
Bandls ring seen in obstructed labour, shoes fetal compromise

Question 18

Outline the physiology of cervical dilation

Answer 18

Process of enlargement of os uteri
Starts as tightly closed aperture 
Needs to allow passage of fetal head 
Measured in cm
Occurs due to uterine action and pressure from presenting part or intact membranes 
Needs every applied pressure

Question 19

Outline the formation of forewaters

Answer 19

Lower segment forms and stretches
Chorion becomes detached with increased uterine pressure
Part of sac bulges into internal os
6-12mm depth
Well flexed head cuts off fluid in front of head
Forms forewaters

Question 20

Outline the rupture of membranes

Answer 20

Usually rupture at end of first stage
May rupture early if malposition
Maybe be no reason for early rupture but can lead to variable deceleration sin the fetal heart
If do not rupture will appear at vulva as bulging sac covering fetal head - a caul

Question 21

What is fetal axis pressure?

Answer 21

Force of fundal contraction is transmitted to upper pole of the fetus, down the long axis and applied to the presenting abort and the cervix