The physiological changes are a continuation of the
same forces that occurred in the earlier hours of labour,
but activity is accelerated, but does not occur abruptly.
Some women may experience an urge to push before the cervical
os is fully dilated, and other may experience a lull before t...
THE NATURE OF THE TRANSITION
AND SECOND STAGE PHASES
OF LABOUR
the phase between full dilatation of the cervical os, and the birth of
the baby.
Most midwives and labouring women are aware of a transitional
period between the period of cervical dilatation, and the time when
active maternal pushing efforts begin; characterized by
maternal restlessness, discomfort, desire for pain relief, a
PHYSIOLOGY AND CARE DURING THE TRANSITION sense that the process is never ending, and demands to
AND attendants to end the whole process.
SECOND STAGE PHASES OF LABOR Appropriate midwifery care encompasses both knowledge of the
Session 1 usual physiological processes of this phase and of the mechanism of
birth, and insight into the needs and choices of each individual
labouring woman.
The physiological changes are a continuation of the
The formal onset of the second stage of labour is traditionally
same forces that occurred in the earlier hours of labour, confirmed with a vaginal examination to check for full dilatation of
but activity is accelerated, but does not occur abruptly. the cervical os.
Some women may experience an urge to push before the cervical
os is fully dilated, and other may experience a lull before the However,a finding of full cervical dilatation may occur some time
onset of strong expulsive second stage contractions. after this stage has in fact been reached, and maternal behavioral
This latter phenomenon has been termed the resting phase of the changes may be a good indication that expulsive contractions ar
second stage of labour. occurring (Baker and Kenner 1993; Dahlen et al 2013; Downe et al
2013).
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Uterine action The contractions become expulsive as the fetus descends further
Contractions become stronger and longer but may be less frequent, into the vagina.
allowing both mother and fetus regular recovery periods. Pressure from the presenting part stimulates nerve receptors
Membranes often rupture spontaneously in the pelvic floor. This phenomenon is termed the ‘Ferguson
reflex’.
The consequent drainage of liquor allows the presenting part,
either the hard, round fetal head or the buttocks, to be directly As a consequence, the woman experiences the need to push.
applied to the vaginal tissues. This reflex may initially be controlled to a limited extent but
This pressure aids distension. becomes increasingly compulsive, overwhelming and involuntary.
Fetal axis pressure increases flexion of the presenting part, The mother’s response is to employ her secondary powers of
resulting in smaller presenting diameters, more rapid progress and expulsion by contracting her abdominal muscles and diaphragm.
less trauma to both mother and fetus.
If the mother is upright during this time, these processes are
optimized.
Soft tissue displacement The levator ani muscles dilate, thin out and are displaced
As the fetal head descends, the soft tissues of the pelvis become laterally, and the perineal body is flattened, stretched and
displaced. thinned.
Anteriorly, the bladder is pushed upwards into the abdomen
where it is at less risk of injury during fetal descent. The fetal head becomes visible at the vulva, advancing with each
This results in the stretching and thinning of the urethra so contraction and receding between contractions until crowning
that its lumen is reduced. takes place.
Posteriorly the rectum becomes flattened into the sacral curve The head is then born.
and the pressure of the advancing head expels any residual faecal The shoulders and body follow with the next contraction,
matter. accompanied by a gush of amniotic fluid and sometimes of blood.
The second stage culminates in the birth of the baby.
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RECOGNITION OF THE
COMMENCEMENT OF THE SECOND
STAGE OF LABOUR
Progress from the first to the second stage is not always clinically 2. Rupture of the forewaters
apparent. Rupture of the forewaters may occur at any time during labour.
Presumptive evidence 3. Dilatation and gaping of the anus
1. Expulsive uterine contractions Deep engagement of the presenting part may produce this sign
Some women feel a strong desire to push before full dilatation during the latter part of the first stage.
occurs. BUT this can lead to maternal exhaustion and/ or cervical 4. Anal cleft line
oedema or trauma. Some midwives have reported observing this line (also called ‘the
purple line’) as a pigmented mark in the cleft of the buttocks which
gradually ascends the anal cleft as the labour progresses (Hobbs
1998; Wickham 2007).
There is some observational evidence from one study that this sign
appears in the majority of women during labour, and that it is
somewhat correlated to both cervical dilatation and position
of the fetal head (Shepherd et al 2010).
The efficacy of this observation in practice in large populations of
women remains to be tested formally.
3
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