Physiology and Care during Transition & Second Stage of Labour

1. C H A P T E R 1 7 Physiology and care during the transition and second stage phases of labour Dr. Areefa Albahri

2. The chapter aim s to • consider the nature of the transition and second stage phases of labour • describe the usual sequence of events during these stages • summarize signs of transition and of the expulsive phase of labour • discuss the care of the mother, father and birth companions • review the observations that should be carried out at this time • discuss the physiology of birth and the role of the midwife when the term fetus is presenting by the breech.

3. The nature of the transition and second stage phases of labour The second stage is 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. This is typically characterized by maternal restlessness, discomfort, desire for pain relief, a sense that the process is never-ending, and demands ' to end the whole process.

4. Uterine action Contractions become stronger and longer but may be less frequent, allowing both mother and fetus regular recovery periods. The membranes often rupture spontaneously towards the end of the first stage or during transition to the second stage. Fetal axis pressure increases flexion of the presenting part, resulting in smaller presenting diameters, more rapid progress and less trauma to both mother and fetus. If the mother is upright during this time, these processes are optimized.

5. Soft tissue displacement  As the fetal head descends, the soft tissues of the pelvis become displaced. 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 contraction and receding between contractions until crowning takes place. The head is then born. The shoulders and body follow with the next contraction, accompanied by a gush of amniotic fluid and sometimes of blood. The second stage culminates in the birth of the baby.

6. Recognition of the commencement of the second stage of labour A. Presumptive evidence 1. Expulsive uterine contractions Some women feel a strong desire to push before full dilatation occurs. Traditionally, it has been assumed that an early urge to push will lead to maternal exhaustion and/or cervical o-edema or trauma. More recent research indicates that the early pushing urge may in fact be experienced by a significant minority of women, and that, in certain circumstances, spontaneous early pushing may be physiological. It is not clear whether these findings are influenced by factors such as maternal or fetal position, or parity, and there is not enough evidence to date to determine the optimum response to the early pushing urge.  

7. 2. Rupture of the fore waters Rupture may occur at any time during labour. 3. Dilatation and gaping of the anus Deep engagement of the presenting part may produce this sign during the later part of the first stage. 4. Anal cleft line 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 as the labour progresses.

8. 5. Appearance of the rhomboid of Michaelis It presents as a dome-shaped curve in the lower back, and is held to indicate the posterior displacement of the sacrum and coccyx as the fetal occiput moves into the maternal sacral  

9. 6. Upper abdominal pressure & epidural analgesia

10. 7. Show This is the loss of bloodstained mucus which often accompanies rapid dilatation of the cervical os towards the end of the first stage of labour. It must be distinguished from frank fresh blood loss caused by partial separation of the placenta or a ruptured vasa praevia.

11. 8. Appearance of the presenting part Excessive moulding of the fetal head may result in the formation of a large caput succedaneum which can protrude through the cervix prior to full dilatation of the os. Very occasionally, a baby presenting by the vertex may be visible at the perineum at the same time as remaining cervix. This is more common in women of high parity. Similarly a breech presentation may be visible when the cervical os is only 7–8 cm dilated.

12. B. Confirmatory evidence In many midwifery setings, it is held that a vaginal examination must be undertaken to confirm full dilatation of the cervical os. This is both to ensure that a woman is not pushing too early, and to provide a baseline for timing the length of the second stage of labour.

13. Phases and duration of the second stage Two distinct phases in second stage progress have been recognized in some women. These are the latent phase, during which descent and rotation occur, and the active phase, with descent and the urge to push.

14. The latent phase In some women, full dilatation of the cervical os is recorded, but the presenting part may not yet have reached the pelvic outlet. Women in this situation may not experience a strong expulsive urge until the head has descended sufficiently to exert pressure on the perineal tissues. It is hypothesized that the prolongation of second stage progress when epidural analgesia is used is due to the relaxation effect of epidural analgesia on the pelvic floor muscles, meaning that the fetal presenting part does not encounter the necessary resistant force from the pelvic floor to bring about the normal rotation process. This tends to be particularly evident in nulliparous women. Passive descent of the fetus can continue with good midwifery support for the woman until the head is visible at the vulva, or until the woman feels a spontaneous desire to push.

15. The active phase Most women without epidural analgesia will experience a compulsive urge to push, or bear down, once the fetal head has rotated and started to descend. The phase of labour that involves active bearing down is termed the active second stage of labour. Duration of the second stage There is no good evidence about the absolute time limits of physiological labour. The second stage of labour can last for up to three hours or so before the risk of maternal and/or fetal compromise begins to increase. In the presence of regular contractions, maternal and fetal wellbeing, and progressive descent, considerable variation between women is to be expected.

16. Maternal response to transition and the second stage • Pushing • Traditionally, if the maternal urge to push occurs before confirmation of full dilatation of the cervical os, or the appearance of a visible vertex, the mother has been encouraged to avoid active pushing. This has been done to conserve maternal effort and allow the vaginal tissues to stretch passively. Techniques to avoid active pushing efforts in this situation include: • position change, left lateral. • using controlled breathing. • inhalation analgesia. • or even narcotic or epidural pain relief.

17. Position If the woman lies flat on her back, resulting in hypotension. This can lead to reduced placental perfusion and diminished fetal oxygenation. The semi-recumbent or supported siting position, with the thighs abducted, is the posture most commonly used in Western cultures. While this may afford the midwife good access and a clear view of the perineum, the woman's weight is on her sacrum, which directs the coccyx forwards and reduces the pelvic outlet. In addition, the midwife needs to bend forward and laterally to support the birth, which may lead to injury.

18. Left lateral position This position was widely used in the United Kingdom (UK) in the 20th century, although it is less common in current practice. The perineum can be clearly viewed and uterine action is effective, but an assistant may be required to support the right thigh, which may not be ergonomic. It provides an alternative for women who find it difficult to abduct their hips. It may also aid fetal rotation, especially in the context of epidural analgesia (Downe et al 2004).

20. Upright positions: squatting, kneeling, all-fours, standing, using a birthing ball Many women find that being upright – whether kneeling, sitting, squatting, or even standing – is more comfortable than lying down at this point. Plus, it may put gravity to work for you. These included reduced duration of second stage labour, fewer assisted births, fewer episiotomies, reduced severe pain in second stage labour, and fewer abnormal heart rate paferns. However, increased rates of perineal damage and of estimated blood loss >500 ml also occurred. There are a number of studies relating to positions and mobility for women using so-called ‘walking epidurals’, but recent data on the physiology of labour and birth for women in spontaneous labour who mobilize without the use of pharmacological pain relief do not seem to exist.

22. Radiological evidence demonstrates an average increase of 1 cm in the transverse diameter and 2 cm in the anteroposterior diameter of the pelvic outlet when the squafing position is adopted. This produces an average 28% increase in the overall area of the outlet compared with the supine position (Russell 1969). Some women find the all- fours position to be the optimum approach for all or part of their labours, especially in the case of an occipitoposterior position, due to relief of backache. It is important not to insist on any position as the ‘right’ one. Positive and dramatic effects on labour progress can be achieved by encouraging the woman to change and adapt her position in response to the way her body feels.

23. . A full understanding of the mechanism of labour should enable the midwife to adapt to any position that the woman wishes to adopt, ensuring in the process that the postures adopted by the midwife are protective of her own health (and, specifically, of her back).

24. Maternal and fetal condition If the woman has had analgesia, or if there is any concern about her wellbeing or that of her baby, then more frequent or continuous monitoring may limit the choices available to her. However, there are often creative solutions to these situations, and good midwifery care involves finding these solutions where possible.

25. The mechanism of normal labour (cephalic presentation) As the fetus descends, soft tissue and bony structures exert pressures that lead to descent through the birth canal by a series of movements. Collectively, these movements are called the mechanism of labour . Knowledge and recognition of the normal mechanism enables the midwife to anticipate the next step in the process of descent. Understanding and constant monitoring of these movements can help to ensure that normal progress is recognized, that the woman gives birth safely and positively, or that early assistance can be sought should any problems occur. . Principles common to all mechanisms are: descent takes place.

26. At the onset of labour the most common presentation is the vertex and the most common position either left or right occipitoanterior; therefore it is this mechanism which will be described. In this instance: the presenting part is the posterior part of the anterior parietal bone. the lie is longitudinal the presentation is cephalic the position is right or left occipitoanterior the attitude is one of good flexion the denominator is the occiput

30. Main movements of the fetus Descent Descent of the fetal head into the pelvis often begins before the onset of labour. For a primi-gravid woman this usually occurs during the later weeks of pregnancy. In multigravid women muscle tone is often more lax and therefore descent and engagement of the fetal head may not occur until labour actually begins. Following rupture of the forewaters and the exertion of maternal effort, progress speeds up.

31. Flexion This increases throughout labour. pressure exerted down the fetal axis will be more forcibly transmitted to the occiput than the sinciput. The effect is to increase flexion which results in smaller presenting diameters that will negotiate the pelvis more easily. At the onset of labour the suboccipito-frontal diameter, which is approximately 10 cm, is presenting. With greater flexion, the sub-occipitobregmatic diameter, that is, approximately 9.5 cm, presents.

32. Internal rotation of the head During a contraction, the leading part is pushed downwards onto the pelvic floor. The resistance of this muscular diaphragm brings about rotation. As the contraction fades, the pelvic floor rebounds, causing the occiput to glide forwards. As discussed above, resistance is an important determinant of rotation, as demonstrates. This explains why rotation is often delayed following epidural analgesia, which causes relaxation of pelvic floor muscles.

34. Extension of the head Once crowning has occurred, the fetal head can extend, pivoting on the suboccipital region around the pubic bone. This releases the sinciput, face and chin, which sweep the perineum, and then are born by a movement of extension, (A) Birth of the head. (B) Restitution. (C) External rotation

35. Restitution The twist in the neck of the fetus which resulted from internal rotation is now corrected by a slight untwisting movement. The occiput moves of a circle towards the side from which it started. Internal rotation of the shoulders The shoulders undergo a similar rotation to that of the head to lie in the widest diameter of the pelvic outlet, namely anteroposterior. The anterior shoulder is the first to reach the levator ani muscle and it therefore rotates anteriorly to lie under the symphysis pubis. This movement can be clearly seen as the head turns at the same time (external rotation of the head). It occurs in the same direction as restitution, and the occiput of the fetal head now lies laterally.

36. Lateral flexion When the woman is in a supported siting position, the anterior shoulder is usually born first, although midwives who encourage women to adopt an upright or kneeling positions have observed that the posterior shoulder is commonly seen first. In the former case, the anterior shoulder slips beneath the sub-pubic arch and the posterior shoulder passes over the perineum. In the later the mechanism is reversed. This enables a smaller diameter to distend the vaginal orifice than if both shoulders were born simultaneously.

37. Midwifery care in transition and the second stage Observations during the second stage Four factors determine whether the second stage is continuing safely, and these must be carefully monitored: Uterine contractions Descent, rotation and flexion of the presenting part Fetal condition/suspicious or pathological changes in the fetal heart Maternal condition.

38. Uterine contractions The strength, length and frequency of contractions should be assessed regularly by observation of maternal responses, and by uterine palpation during the second stage of labour. They are usually stronger and longer than during the first stage of labour, with a shorter resting phase.

39. Fetal condition/suspicious or pathological changes of the fetal heart If the membranes are ruptured, the liquor is observed to ensure that it is clear. While thin old meconium staining is not always regarded as a sign of fetal compromise. The midwife should learn to recognize the normal changes in fetal heart rate patterns during the second stage, both when monitored continuously (where there are specific risk factors) and when monitored intermittently. This will minimize the risk of iatrogenic intervention, and maximize a timely response to fetal compromise if it occurs.

40. If the woman is labouring normally, NICE guidelines recommend that a Pinard's stethoscope or other hand-held system such as a Sonic aid should be used to monitor the fetal heart intermittently (NICE 2007). During the second stage this is usually undertaken immediately after a contraction, with some readings being taken through a contraction if the woman can tolerate this. Late decelerations, and a lack of return to the normal baseline, a rising baseline or diminishing beat-to-beat variation, are signs of concern.

41. Maternal condition The midwife's observation includes an appraisal of the woman's ability to cope emotionally as well as an assessment of her physical wellbeing. This includes close attention to what she says, as well as how she behaves, and a with supportive response to any indication that she is losing belief in herself to accomplish the birth of her baby. Maternal pulse rate is usually recorded half-hourly and blood pressure every few hours, provided that these remain within normal limits. If the woman has an epidural in situ, blood pressure will be monitored more frequently, and continuous electronic fetal monitoring will probably be in use.

42. Maternal comfort As a result of her exertions the woman usually feels very hot and sticky, and she will find it soothing to have her face and neck sponged with a cool flannel. Her mouth and lips may become very dry. Sips of iced water or other fluids are refreshing and a moisturizing cream can be applied to her lips. Her partner may help with these tasks as a positive contribution to ease her discomfort. The bladder is vulnerable to damage, due to compression of the bladder base between the pelvic brim and the fetal head. The risk is increased if the bladder is distended. The woman should be encouraged to pass urine at the beginning of the second stage unless she has recently done so.

43. Preparation for the birth Once active pushing commences, the midwife should prepare for the birth. The room in which the birth is to take place should be warm with a spotlight available so that the perineum can be easily observed if necessary. A clean area should be prepared to receive the baby, and waterproof covers provided to protect the bed and floor. Sterile cord clamps, a clean apron, and sterile gloves are placed to hand. In some setings, sterile gowns are also used. An oxytocic agent may be prepared, either for the active management of the third stage if this is acceptable to the woman, or for use during an emergency. A warm cot and clothes should be prepared for the baby.

44. Birth of the baby The midwife's skill and judgment are crucial factors in minimizing maternal trauma and ensuring an optimal birth for both mother and baby. These qualities are refined by experience but certain basic principles should be applied. They are:

45. observation of progress. • prevention of infection. • emotional and physical comfort of the mother. • anticipation of normal events. • support for the normal processes of labour. • recognition of abnormal developments. • appropriate management to complication.

46. Birth of the head Once the birth is imminent, the perineum may be swabbed clean of any mucus and a clean pad is placed under the woman to absorb any faeces or fluids. If she is not in an upright position a pad is placed over the rectum on the perineum (but not covering the fourchette) and a clean towel is placed on or near the woman for receipt of the baby. Throughout these preparations the midwife observes the progress of the fetus. With each contraction the head descends. The head recedes between contractions, which allows these muscles to thin gradually.

47. The skill of the midwife in ensuring that the active phase is unhurried helps to safeguard the perineum from trauma, either observing the gradual advancement of the fetal head or controlling it with light support from her hand. One large study, indicated that, compared with guarding the perineum, a hands-off technique????? was associated with slightly more maternal discomfort at 10 days postnatally (McCandlish et al 1998). The hands-off technique was also associated with a lower risk of episiotomy, but a higher risk of manual removal of placenta. There is some debate about the generalizability of this trial to all sefings and positions in labour.

49. Most midwives place their fingers lightly on the advancing head to monitor descent and prevent very rapid crowning and extension, which are believed to result in perineal laceration (see (Fig. 17.5). Excessive pressure on the head, however, may be associated with vaginal lacerations. Whatever technique the midwife adopts, it should be based on the assumption that it is the woman who is giving birth to her baby, and the midwife is thereto add the minimum physical help necessary at any given time.

50. Supporting the head. (A) Preventing rapid extension. (B) Controlling the crowning. (C) Easing the perineum to release the face.