Gab Kovacs1 and Paula Briggs2
(1)
Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
(2)
Sexual and Reproductive Health, Southport and Ormskirk Hospital, Southport, UK
Definitions
The Stages of Labour
The First Stage
Progress During the First Stage
Foetal Distress
Maternal Distress
The Second Stage
Normal Vaginal Delivery
Lower Uterine Segment Caesarean Section (LUSCS)
Assisted Delivery (Forceps or Vacuum)
The Third Stage
Definitions
The Stages of Labour
Labour is divided into three stages:
Stage I - From the onset of labour until full dilatation of the cervix.
The precise onset of labour is difficult to define. Technically, it starts with the commencement of dilatation of the cervix. In primagravida this is preceded by effacement (thinning of the cervix) and this is diagnosed by vaginal examination. Three imprecise “markers” can be used as possible milestones to gauge the onset of labour (Table 21.1):
Table 21.1
Stages of labour
|
Onset |
End |
|
|
1st stage |
Onset of contractions |
Full dilatation |
|
2nd stage |
Full dilatation |
Delivery of baby |
|
3rd stage |
Delivery of baby |
Delivery of placenta and membranes |
1.
2.
3.
Stage II - From full dilation of the cervix, until the delivery of the baby.
Stage III - From delivery of the baby until delivery of the placenta and membranes.
The First Stage
Every labour should be considered as a “trial of labour”. The goal for most women is a “normal vaginal delivery”, but one needs to be prepared to proceed to a surgical delivery in the event of one of the following three complications arising:
1.
2.
3.
Progress During the First Stage
This is assessed using both abdominal and vaginal examination.
The two “Key Performance Indicators” are descent of the presenting part, and dilatation of the cervix.
These two parameters are recorded on a partogram, which documents progress, and also highlights if there is a delay.
Descent of the presenting part during labour is monitored by both abdominal and vaginal examination. The station on abdominal examination is described as, “how many finger breadths of head are palpable above the pelvic brim”. The foetal head measures approximately 10 cm in diameter. The foetal head can be divided into five fifths, corresponding to five finger breadths (Fig. 21.1). As the foetal head enters the pelvic brim, five finger breadths are palpable. During labour this reduces sequentially to one finger breadth and then nil.
Fig. 21.1
The feral head- five fingers
Once the head is engaged – the widest diameter of the presenting part has passed through the pelvic inlet- only two fingers of head are palpable above the pelvic brim (Fig. 21.2).
Fig. 21.2
The foetal head “engaged”
In order to better understand the relationship between the pelvis and the foetal head, imagine that the pelvis is a “box” about 10 cm wide, and 10 cm long (Fig. 21.3).
Fig. 21.3
The pelvis as a “box”
Once the head is engaged, at least 6 cm of head are within the pelvis (the imaginary box) and the vertex is about 4 cm above the ischial spines (Fig. 21.2).
Once a primagravida has passed through the latent phase, the cervix should dilate at approximately a rate of 1 cm for each hour of labour. The latent phase precedes this and during this time the cervix effaces and dilates to 3 cm, which may take 8–12 h.
The foetal head (in a cephalic presentation) should steadily descend (as described in Chap. 5), so that by the end of the first stage, it is totally in the pelvis, with no foetal head palpable above the pelvic brim, and the presenting part at, or below, the ischial spines (Fig. 21.4).
Fig. 21.4
The foetal head in the pelvis at the end of the first stage of labour
Progress is delayed.
If the foetal head is not descending, and the cervix is not dilating at the expected rate, progress is “delayed”.
A common cause for this is if the woman is not in established labour.
A woman’s labour is assessed by timing her contractions over a representative 10 min period. For established labour, one would expect three to four contractions of medium to strong intensity lasting at least 60 seconds. When labour is assessed manually, the foetal heart should be auscultated and counted after each contraction, to detect decelerations.
The quality of contractions can be monitored electronically by external or internal pressure monitors. This can be combined with continuous foetal heart rate monitoring – cardiotocograph (see below).
If the woman is not in established labour, the labour may be augmented with a syntocinon infusion, unless there are contraindications. The concentration and rate of infusion of syntocinon is increased until three to four strong contractions occur every 10 min.
If there is “failure to progress” over a 4 h period despite established labour, a diagnosis of “obstructed labour” is highly likely, and operative delivery needs to be considered.
The duration of the first stage of labour in a primagravida should be under 20 h (8–12 h latent, 8 h active). In a multigravida this tends to last 8–10 h, but is far more unpredictable.
Foetal Distress
The first sign that the foetus may be distressed (hypoxic due to some compromise of its oxygen supply) is the appearance of meconium in the liquor. This signifies that the foetus has passed meconium, similar to a person opening their bowels when severely stressed.
A more accurate assessment of the foetal condition can be obtained by assessing the pattern of the foetal heart rate. This can be auscultated, using a stethoscope or pinnard or more commonly with a hand held ultrasound (Doppler), or can be monitored electronically with a foetal heart monitor (cardiotocography CTG). There are both external monitors attached to the abdomen, which detect the foetal heart beat, or internal monitors, attached to the foetal scalp (used only after membranes are ruptured) – direct foetal ECG recording.
The important observation is the relationship between the foetal heart rate and uterine contractions. During uterine contractions, due to the raised intrauterine pressure, the foetal heart rate often slows, but recovers quickly as soon as the contraction ceases. If there is a degree of foetal distress, the recovery in heart rate is delayed.
CTG Patterns.
1.
2.
3.
4.
What to do if the CTG is abnormal:
· Inadequate trace – check connections, apply foetal scalp electrode, compare foetal heart rate with maternal pulse.
· Excessive uterine contractions – if syntocinon has been given, stop or reduce flow.
· Consider using tocolytics eg. beta agonists, calcium channel blockers and prostaglandin synthetase inhibitors.
· Maternal tachycardia – check maternal temperature, hydration status and blood pressure.
· Consider other maternal adverse effects
· Positional – roll onto left lateral position
· Recent top-up of epidural
· Recent use of bed pan or vomiting
If no reversible factor present and trace continues to be abnormal, either perform foetal blood sampling (FBS) or expedite delivery.
Foetal blood sampling is used if the foetal heart monitoring suggests distress, or if it does not give enough information about the well-being of the baby. This test is done through an examination cone, which is placed on the baby’s head. The scalp is cleansed and is then punctured. The blood sample is aspirated via a thin plastic tube, and is sent to the laboratory, where the pH of the blood sample is determined. A level above 7.25 is considered normal, 7.20–7.25 borderline, and below 7.20 suggests the baby is not getting enough oxygen, and delivery should be expedited.
Possible future developments for foetal surveillance in labour:
Devices for continuous foetal blood oxymetry are being developed. Computerised programmes for interpreting FHR are also in development.
Maternal Distress
It is unusual to have to terminate labour because of maternal distress.
Maternal pain can be controlled with nitrous oxide inhalation, narcotic analgesia, or epidural analgesia. Hydration, and nutrition can be controlled with intravenous infusion of glucose and/or saline.
Occasionally, if the woman has a medical condition, or can no longer cope the foetus will need to be delivered.
The Second Stage
Normal Vaginal Delivery
The role of the practitioner is to guide the foetus through the vagina and perineum without undue delay, and with minimal damage to the foetus or the mother.
This initially requires that the presenting part is controlled, so that as the mother pushes, the foetal head does not come out too quickly, which may damage the foetus or cause tears of the perineum. The practitioner needs to lean on the head to provide control against the woman pushing, which she does with each contraction.
Once the head is delivered, it is pushed downwards, so that cord around the baby’s neck can be detected. If present it is either looped over the head, or clamped with forceps and cut. The baby’s face is wiped and the nose and throat are usually aspirated to remove blood and mucus. The baby can now breathe, although the body is still within the pelvis, and expansion of the lungs is restricted.
The head is the rotated, and the anterior shoulder is delivered with downward traction. If there is difficulty delivering the anterior shoulder (shoulder dystocia), the bottom of the bed needs to be lowered to allow extra downward traction. Once the anterior shoulder is delivered the foetus is elevated to deliver the posterior shoulder, watching the perineum to avoid tearing. The foetus is then delivered, the cord is cut and clamped, and the Apgar score is recorded.
The baby is then wrapped in a cloth and kept warm. If spontaneous respirations are not immediately established, signified by the baby crying, resuscitation should commence immediately.
Sometimes a medio-lateral episiotomy is cut to increase the size of the introitus, and avoid tearing and facilitate delivery.
Once a tear starts, it cannot be controlled, and may extend into the skin or even through the muscle of the anus.
Tears are classified as first, second, third or fourth degree:
· First degree – only involves the vaginal epithelium
· Second degree – involves underlying muscle
· Third degree – involves external anal sphincter muscles
· Fourth degree – involves internal anal sphincter muscles and ano-rectal mucosa
The second stage should be completed within 3 h (1 h for descent, 2 h of pushing) in a primagravida unless there is foetal distress. In a woman who has had a previous vaginal delivery, the second stage should be significantly shorter.
Lower Uterine Segment Caesarean Section (LUSCS)
If cervical dilatation has not reached 10 cm, and the presenting part has not descended to the ischial spines, with no progress over 4 h despite established labour, then Caesarean Section is indicated. This can be performed under epidural/spinal anaesthesia or less commonly under general anaesthesia.
Assisted Delivery (Forceps or Vacuum)
Assisted delivery (forceps or vacuum) may be undertaken if the cervix has fully dilated.
The prerequisites for a vaginal instrumental delivery are:
1.
2.
3.
4.
5.
6.
The Third Stage
The third stage is usually assisted. Once the baby is delivered and it is confirmed that the uterus is empty, an injection of syntometrine, which causes uterine contractions, is administered. This promotes the separation of the placenta. The signs suggesting that this has taken place are, the lengthening of the cord and a fresh show of blood. This facilitates delivery of the placenta with controlled traction with the right hand, whilst the left hand supports the uterine fundus above the symphysis.
Care has to be taken not to pull on an unseperated placenta as this can cause uterine inversion, hypotension and shock.
If the placenta is not be delivered with 30 min, manual removal should be considered.
Postpartum haemorrhage is discussed in Chap. 26.