Chapter 24 Obstetric operations
INDUCTION OF LABOUR
Induction of labour may be required to ‘rescue’ the fetus from a potentially hazardous intra-uterine environment in late pregnancy for a variety of reasons, or because continuation of the pregnancy is dangerous to the expectant mother. Indications for induction of labour are listed in Table 24.1.
Table 24.1 Indications for induction of labour: Australia
| Indication | Proportion of Inductions |
|---|---|
| Prolonged pregnancy (41 or more weeks) | 26% |
| Hypertensive disorders | 12% |
| Prelabour/prolonged rupture of membranes | 10% |
| Diabetes – pregestational and gestational | 7% |
| Intra-uterine growth restriction | 5% |
| Non-reassuring fetal status | 2% |
| Fetal death in utero (FDIU) | 1% |
| Blood group isoimmunization | 0.2% |
| Chorioamnionitis | 0.1% |
| Social induction | 16% |
| Others | 21% |
The method adopted depends on:
Fig. 24.1 The relationship between the condition of the cervix and success rate of surgical induction.
The highest rate of success, (i.e. that the induction is followed by a vaginal birth within 24 hours) occurs in a woman whose cervix is favourable and whose Bishop score is 5 or more (Table 24.2).
If the chances of success are evaluated as low, the doctor may recommend caesarean section.
Techniques of inducing labour
Labour may be induced by drugs, by the surgical technique of amniotomy, which is also known as artificial rupture of the membranes (ARM), or by mechanical stimulation of the cervix.
Induction of labour using drugs
Two agents are available: prostaglandins and oxytocin.
Prostaglandins
Three prostaglandins with different properties are used.
Oxytocin (Syntocinon)
Oxytocin should always be administered by intravenous infusion, preferably using an infusion pump. If it is used alone, 50% of women will be in labour within 12 hours. Induction is more effective if preceded by PGE2 vaginal pessaries or following amniotomy.
The infusion rate is increased by 5 mU/min every 30 minutes until contractions lasting longer than 60 seconds recur at 3–5-minute intervals. The maximum rate used is 60 mU/min. Because of the risk of water intoxication, the quantity of fluid infused should not exceed 1500 mL in 10 hours.
Surgical induction of labour (amniotomy)
Surgical induction of labour (amniotomy) is more effective if the cervix is favourable (Bishop score 5+). The patient is placed in the dorsal or lithotomy position and the vagina swabbed with antiseptic. Two of the doctor’s fingers are inserted to reach the cervix and, if practicable, one is inserted through the cervix to ‘sweep’ the membranes. An amnihook, or a Kocher forceps, is introduced along the intravaginal fingers and the membranes below the fetal head (the forewaters) are broken with the instrument.
The problems following amniotomy are:
A suggested schema (flow chart) for the induction of labour is shown in Figure 24.2.
As can be seen from the flow chart, if the cervix is ‘unfavourable’ (i.e. a low Bishop score), the drugs mentioned may be used to ripen the cervix so that surgical induction, if needed, will be more effective. In the flow chart PGE2 is featured, but the other prostaglandins listed above are equally effective.
Mechanical methods
A single (e.g. Foley) or double (Atad) balloon catheter is also an effective method of inducing labour. The catheter is passed aseptically through the cervix and the balloon(s) are inflated with sterile saline. The woman is then free to ambulate and is assessed 6 or so hours later, unless she goes into labour or the membranes rupture. Other devices, such as the hydrophilic laminaria tent have been used. They swell by absorbing fluid and so slowly dilate the cervix.
The principal benefits of balloon catheters are the induction of labour in women who have previously had a caesarean section; this avoids the potential hyperstimulation that may occur with prostaglandins, or the theoretical softening of the collagen fibres in the uterine scar.
AUGMENTATION OF LABOUR
In cases where the quality of the uterine contractions is poor (see p. 174), their strength may be augmented by performing ARM and, if necessary, by setting up an incremental oxytocic infusion, or both.
INSTRUMENTAL DELIVERY
In the second stage of labour situations may arise wherein it becomes necessary to deliver the baby. These are:
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