Chapter 37 Care in the second stage of labour

• understand maternal behaviours associated with transition and the expulsive stage of labour

• have enhanced your knowledge of the basic physiology of transition and the second stage

• understand some of the techniques that are currently used in childbirth

• recognize that many midwifery practices in the area of physiological birth are based on empirical but not formal evidence

• understand the importance of clear, comprehensive, accurate record-keeping.

Introduction

The anatomical second stage of labour has been traditionally defined as the period from full dilatation of the os uteri to the birth of the baby. However, women do not experience labour and birth by its anatomical divisions, or by the dilatation of the cervix (Gross et al 2006), and labours do not usually progress at a uniform rate.

The distinctive physiological changes that occur just before or around the time the cervical os is fully dilated are traditionally defined as ‘transition’. There is a paucity of formal evidence about the nature of transition, although some observational studies have been undertaken (Crawford 1983, Roberts & Hanson 2007). During or following this phase, the woman begins to feel a variable urge to bear down. Anecdotal evidence indicates that it is not uncommon for midwives to offer women pharmacological pain relief if the urge to bear down occurs when vaginal examination indicates that the anatomical second stage is still some way off. If she then progresses more quickly than expected, such pain relief may inhibit the natural urge to bear down actively. It is thus essential that midwives know how to recognize the transitional phase of labour, and how to support women effectively at this time.

Signs of progress

Transition

Transition occurs at variable times between the late first stage and early second stage of labour. It is recognizable by a change in the behaviour of the woman, and, sometimes, by a change in the nature of the contractions she is experiencing. Any or all of the following may be noted:

• loss of control; panic

• belief that she cannot carry on

• fearfulness (sometimes of dying)

• disorientation

• nausea

• uncontrollable shivering

• demands for pain relief

• a need to shout and scream

• a slowing of contractions

• a heavy ‘show’ – a loss per vaginam, which is usually a mixture of blood and mucus

• a period when the woman dozes, and goes ‘inside herself’ (the so-called ‘rest and be thankful’ phase)

• a variable urge to bear down or to push.

If a vaginal examination is undertaken, the mother’s cervical os will typically be found to be between 7 and 9 cm dilated, though smaller dilations have been reported (Downe et al 2008). There have been occasional reports of transition (evidenced by an early pushing urge) occurring when the cervical os is less than 7 cm dilated (Roberts et al 1987).

Reflective activity 37.1

Next time you are with a woman in transition and/or the expulsive phase of labour, ask yourself the following questions. If the answers conflict with local guidelines, or with the usual actions midwives are expected to take locally, consider how these guidelines or informal expectations can be examined by you and your colleagues, with a view to revision.

• Does she want/need pain relief? Could reassurance, support, and faith in her capacity to birth the baby be just as effective?

• Will firm direction be helpful for her, or will it lead her to panic?

• If her contractions are decreasing in length and strength, is this due to underlying pathology, or is it only part of a physiological transition? Does she need to rest for a short time? Is she hungry?

• Is she well hydrated?

• Does she want to be touched or not?

• Is the early pushing urge being felt because of fetal malposition, or is the head just descending very rapidly? Should she push spontaneously if you are not sure the cervical os is fully dilated?

• Is she enabled to adopt any position she wants? What would you do if she throws her arms back and brings her hips forward when she begins pushing?

• Is it difficult not to say ‘hold your breath and push’?

Expulsive phase

Initially, the strength and consistency of the pushing urge usually varies in intensity, becoming more consistent over time. The woman usually makes a characteristic grunting noise at the height of the contraction. She may feel that her bowels are emptying, which may be very embarrassing for her. The perineum bulges and is stretched thin as it is distended by the descending fetus. The anus initially pouts and then dilates with contractions. The vagina begins to gape, and finally the presenting part is visible.

Some midwives have noted the appearance of a rounded area at the level of the lower back, the so-called rhombus of Michaelis (Sutton & Scott 1996). Sutton & Scott note that it is caused by ‘the pressure of the fetal head [which] … lifts the sacrum and the coccyx out of the way’. They also observe that the woman’s instinctive reaction to the descent of the fetus is to arch her back, push her buttocks out (or off the bed if she is semi-recumbent) and throw her arms back to grasp onto any fixed object behind her. They hypothesize that this is a physiological response, since it causes a lengthening and straightening of the curve of Carus, optimizing the fetal passage through the birth canal.

Others have noted anecdotally that women who have an epidural in situ may experience discomfort under the ribs at around about the time of full cervical dilatation. This may be a function of fetal re-alignment as the fetal head descends, causing a sensation of pressure above the level of the epidural block. The efficacy of these observations in predicting the onset of the second stage of labour for individual women remains to be researched.

If necessary, the midwife can carry out a vaginal examination to confirm full dilatation of the os uteri. If no cervix is felt, there is positive confirmation of the onset of the anatomical second stage of labour.

Physiology of the second stage of labour

Contractions

On average, at this stage, studies have indicated that contractions have an amplitude of 60–80 mmHg, occur every 2–3 minutes and last for 60–70 seconds, although other patterns of second stage contractions can be effective. Marked retraction of the uterus further aids the descent of the fetus through the birth canal. There is no appreciable fall in the height of the fundus, however, because the fetal back tends to uncurl from its flexed attitude and the lower uterine segment stretches. The force of the uterine contractions and secondary powers is transmitted down the fetal spine to its head. This is fetal axis pressure and helps the descent of the fetus through the birth canal.

Secondary powers

The expulsion of the fetus is further aided by the voluntary muscles of the diaphragm and abdominal wall. As the presenting part descends to approximately 1 cm above the level of the ischial spines, pressure from the fetal presentation stimulates nerve receptors in the pelvic floor, and the woman experiences the desire to bear down. This is termed the ‘Ferguson reflex’ (Ferguson 1941). This sensation may occur prior to the end of the anatomical first stage of labour, or at cervical full dilatation. The voluntary muscles of the chest and abdominal wall act reflexively in concert with the uterine contractions to overcome the resistance of the vagina, pelvic floor muscles, and external parts. During this process, the diaphragm is lowered and the abdominal muscles contract.

The pelvic floor

The advancing fetus gradually stretches the vagina and displaces the pelvic floor. Anteriorly, the pelvic floor is pushed up and the bladder is drawn up into the abdomen, where it is less likely to be damaged. Posteriorly, the pelvic floor is pushed down in front of the presenting part. The rectum is compressed; thus any faecal contents will be expelled. The perineal body becomes elongated and paper-thin as it is flattened by the advancing fetus.

Mechanism of labour

As labour progresses, the fetus is moved through the birth canal and induced to make various twists and turns due to the forces which occur, causing it to respond to the contours and planes of the maternal pelvis. These movements are called, collectively, the mechanism of labour. An understanding of this mechanism enables assessment of progress in labour, and recognition of when physiological support may be required, or if a call for assistance should be made.

There is a mechanism for every fetal presentation and position. The widest diameter of the brim of the pelvis is transverse, whereas the widest diameter of the outlet is anteroposterior. To make the best use of available space, the widest presenting diameter of the fetal head usually enters the pelvis in the transverse diameter. As it descends, the fetal head and then the shoulders rotate to emerge in the anteroposterior diameter. The mechanism for the most common presentation is as follows, although it should be noted that the specific physiology of individual women and fetal pairs can alter this mechanism.

The lie is longitudinal, the presentation is cephalic and the presenting part is the area of the vertex. The attitude is one of flexion and therefore the denominator is the occiput. The engaging diameter is the suboccipitobregmatic (on average, approximately 9.5 cm). The position may be either right or left occipitoanterior.

Descent

Descent is the process whereby the fetal head moves into the pelvis (Fig. 37.1). Engagement occurs when the widest diameter of the presenting part enters the pelvis. This is more likely to occur prior to the onset of labour in nulliparous women.

Figure 37.1 Descent of a fetus with a well-flexed head presenting. The sagittal suture is in the transverse diameter of the pelvis. (Mother in upright position.)

Flexion

At the beginning of labour the fetal head is usually in an attitude of natural flexion. As labour progresses, the head meets the resistance of the pelvic floor muscles, and flexion increases. Fetal axis pressure is then transmitted through the occiput, which is pushed down lower as a consequence. The forehead is pushed upwards by the resistance of the soft parts, and so complete flexion is obtained.

Internal rotation

When the occiput meets the resistance of the pelvic floor, it rotates forward 45° (Fig. 37.2). The slope of the pelvic floor aids this internal rotation forwards, allowing the head to emerge in the longest diameter of the pelvic outlet; that is, the anteroposterior diameter (Figs 37.3 and 37.4). The occiput then escapes under the pubic arch and the head is crowned.

Figure 37.2 Internal rotation occurs. The sagittal suture is in the oblique diameter of the pelvis. (Mother in upright position.)

Figure 37.3 Internal rotation complete – further descent occurs. The sagittal suture is now in the anteroposterior diameter of the pelvis. As the head deflexes slightly with descent, the sacrum and coccyx are displaced posteriorly. (Mother in upright position.)

Figure 37.4 The head descended to the vulval outlet. (Mother in upright position.)

Crowning of the head

The head is crowned when it has emerged under the pubic arch and no longer recedes between contractions. The widest transverse diameter of the head (the biparietal diameter) is born (Fig. 37.5).

Figure 37.5 The head is crowned. The sacrum and coccyx regain their normal position. (Mother in upright position.)

Extension

Once the head is crowned, extension takes place to allow the bregma, forehead, face and chin to pass over the perineum.

Restitution

When the head is born, it rights itself with the shoulders (Fig. 37.6). During the movement of internal rotation, the head is slightly twisted because the shoulders do not rotate at that time. The baby’s neck is untwisted by restitution.