Obstetric operations

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Chapter 24 Obstetric operations

CHAPTER CONTENTS

Induction of labour 189

Techniques of inducing labour 189
Augmentation of labour 192
Instrumental delivery 192

Methods and conditions of instrumental delivery 192
Obstetric forceps 192
Vacuum extractor or ventouse 195
Caesarean section 197

Indications for caesarean section 197
Technique of caesarean section 197
Vaginal birth after previous caesarean section 199
Version 199
Destructive operations on the fetus 199

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:

• The duration of the pregnancy
• The condition of the cervix (i.e. favourable or unfavourable) (Fig. 24.1)
• The position of the fetal head in relation to the pelvis.
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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).

Table 24.2 A method of cervical ‘scoring’ (Bishop score)

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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.

• PGE1 gemeprost is available in pessary form or as an intracervical injection system. It is used in the second trimester of pregnancy for the termination of pregnancy and for the induction of labour in cases of fetal death in utero. It should be avoided in the third trimester because of the risk of uterine hypertonicity. Misoprostol is a synthetic PGE1 analogue which compares favourably with PGE1 and PGE2 in its efficacy in inducing labour. It can be administered by placing a tablet (25 μg) in the posterior vaginal fornix every 4 hours. Oral administration appears to be less effective and has been reported to be associated with higher rates of uterine hyperstimulation.
• PGE2 is available as a gel or in pessary form and may be introduced intravaginally or intracervically. The gel appears to be more effective and is associated with a lower risk of producing uterine hypertonicity. PGE2 softens the cervical connective tissue and relaxes cervical muscle fibres, ‘ripening’ the cervix. PGE2 may stimulate the production of PGF2α, which will induce uterine contractions. PGE2 produces cervical ripening when the cervical (Bishop) score is less than 5, and therefore amniotomy is contraindicated. It is available in a prefilled syringe in a dose of 1–2 mg, which is introduced into the posterior vaginal fornix. The patient’s pulse rate, fetal heart rate and uterine activity are monitored for 30 minutes, after which time she may walk about if she wishes, provided the pregnancy is not at high risk. If labour is not established within 6 hours the woman is reassessed. If the cervix is now favourable ARM is performed, otherwise a further dose of PGE2 is given.
• A slow-release pessary (Cervidil). It releases a mean of 4 mg over 12 hours and can easily be removed by its tape if necessary.

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:

• Prolapse of the umbilical cord (0.5% of cases)
• Infection, if the induction–delivery interval is >24 hours.

A suggested schema (flow chart) for the induction of labour is shown in Figure 24.2.

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Fig. 24.2 Induction of labour flow chart.

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:

• Delay in the birth of the baby when the second stage of labour has exceeded 2 hours without regional anaesthesia or 3 hours with regional anaesthesia in a nulliparous woman or the fetal head has been delayed on the perineum for more than 30 minutes. The delay usually occurs because:

• The fetal head has not rotated and is arrested in the transverse diameter of the midpelvic cavity (deep transverse arrest of the head).
• The head has rotated into the posterior position in the midcavity or in the lower pelvic strait (posterior arrest of the head).
• A minor degree of cephalopelvic disproportion is present.
• The uterine contractions have become weaker.

• The fetus shows signs of distress (i.e. bradycardia or the passage of meconium).
• The mother has become distressed, either physically or mentally, in the second stage of labour.
• The mother has an existing obstetric condition, or a medical one (e.g. pre-eclampsia, chronic hypertension, cardiac disease), that may deteriorate during the expulsive stage of labour.
• To aid in the delivery of the aftercoming head in a breech presentation.

Methods and conditions of instrumental delivery

The incidence of instrumental delivery varies between 5 and 12% of all deliveries. Two methods are available. The first, delivery by obstetric forceps, was introduced 400 years ago; the second, delivery by vacuum extraction, was introduced 70 years ago.

The conditions for instrumental delivery are:

• The greatest diameter of the fetal head must have passed the pelvic brim.
• The cervix must be fully dilated.
• The membranes must have ruptured and the bladder must be empty.
• The patient must receive adequate anaesthesia or analgesia. Women requiring a vacuum extraction or a low forceps require a perineal nerve block at the very least. Women requiring a midforceps delivery should have an epidural block, a pudendal nerve block or a general anaesthetic.

Obstetric forceps

From crude beginnings the obstetric forceps has developed into a precision instrument that must be used with great skill to avoid damage to the woman or her fetus. More than four-fifths of forceps deliveries are by low or outlet forceps, which are relatively safe.

Types of forceps delivery

As shown in Figure 24.3, the station of the fetal head is used to describe the type of forceps delivery.

• High forceps deliveries are no longer performed because of the high risk of causing serious fetal and maternal damage. Delivery should be by caesarean section.
• Midforceps. The forceps blades are applied to the sides of the fetal head, whose biparietal diameter has entered the pelvis but has not advanced much beyond the ischial spines. Usually the occiput lies in one or other transverse diameter of the maternal pelvis.
• Low forceps. The forceps blades are applied to the sides of the fetal head, whose biparietal diameter has advanced to or beyond the ischial tuberosities and has rotated so that the sagittal suture lies in the anteroposterior diameter of the maternal pelvis.
• Outlet forceps. The fetal head distends the vaginal introitus, but the perineum is holding it back.
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Fig. 24.3 Types of forceps delivery, showing the station of the head when the forceps is applied.

The short-shanked forceps is used for low or outlet forceps procedures (Fig. 24.4). The long-shanked forceps is used for midforceps delivery after manual rotation of the fetal head if it is arrested in the transverse diameter of the pelvis (Fig. 24.5). They are also suitable for low or outlet deliveries. Kjelland’s forceps has a sliding lock and can be used to rotate the fetal head and deliver it (see Fig. 24.6).

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Fig. 24.4 Wrigley’s forceps (scale × 2 that of Figs. 24.5 and 24.6).

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Fig. 24.5 Simpson’s obstetric forceps.

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Fig. 24.6 Kjelland’s forceps.

All forceps compress the fetal head to some extent and apply traction to effect the birth.

Technique of forceps delivery

The technique of forceps delivery is shown in Figures 24.7–24.15.

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Fig. 24.7 The assembled forceps are held in front of the woman’s vulva, with the pelvic curve uppermost. The left blade is introduced, without force, into the vagina between the fetal head and the vaginal wall, which is protected by the doctor’s fingers; the blade is steered to lie along the left side of the baby’s head.

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Fig. 24.8 When correctly applied the shank will press on the mother’s perineum.

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Fig. 24.9 The right blade is introduced in a similar manner and the two blades are assembled in the lock. If they do not fit easily into the lock there is a misapplication, and if they cannot be made to adjust easily, the forceps is removed and the procedure is repeated.

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Fig. 24.10 The forceps are held as shown and the baby’s head is delivered in a smooth curve, using controlled traction, preferably during a uterine contraction. An episiotomy is often needed to prevent a perineal tear.

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Fig. 24.11 Position of the patient for midforceps delivery.

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Fig. 24.12 Direction of traction in forceps delivery. In midforceps delivery (1) the initial direction of pull is downwards, in low forceps (2) horizontal, and in outlet forceps (3) slightly upwards.

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Fig. 24.13 The mechanics of forceps delivery. Midforceps: with axis traction the force is resolved and the pull is in the axis of the birth canal.

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Fig. 24.14 Manual rotation of the head from a left occipitoposterior position. (A) The left hand is placed on the abdomen and pulls the right shoulder of the baby towards the mother’s right side. Simultaneously, the right hand, in supination, holds the head by its biparietal diameter and rotates it through 180° to a position of pronation. (B) At the end of the manoeuvre the occiput becomes anterior.

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Fig. 24.15 Application of Kjelland’s forceps in cases of deep transverse arrest.

Low or outlet forceps

The use of these is described in Figures 24.7–24.10.

Midforceps

The technique for applying the long-shanked curved forceps is the same as that used to apply the short-shanked forceps. As the forceps blades have to be introduced further into the vagina, great care must be exercised to avoid damaging the vaginal wall and to ensure that the forceps blades are correctly applied along the sides of the fetal head.

Because the head has to be pulled through the pelvic curve, the mother should be positioned correctly, with her legs in stirrups and her buttocks projecting over the end of the bed (see Fig. 24.11). This is because the pull required to deliver the baby has to be downwards initially and then curving upwards (see Fig. 24.12). Some obstetricians use the axis traction device, but skill is required to use it properly (see Fig. 24.13).

If the baby’s head is arrested in the transverse diameter of the midpelvis manual rotation may be attempted (see Fig. 24.14), followed by midforceps delivery. Alternatively, Kjelland’s forceps may be used or a caesarean section performed.

Kjelland’s forceps

This instrument is used to rotate a head arrested in the transverse diameter of the midpelvis. It requires considerable skill and the woman should ideally be delivered in an operating theatre so that, if any difficulty is experienced, a caesarean section can be done immediately.

The forceps is held in front of the woman’s vulva and positioned so that the dot on the shoulders of the instrument points to the side of the pelvis where the baby’s occiput lies. The remainder of the application of Kjelland’s forceps is shown in Figure 24.15. Usually a wide episiotomy is made, as perineal damage is almost inevitable. Alternative methods of delivery are vacuum extraction, manual rotation of the fetal head and forceps delivery, or caesarean section.

Dangers of a difficult forceps delivery

The vagina and cervix may be damaged, causing haemorrhage. Following a midforceps delivery the entire vagina should be inspected with good illumination, and lacerations looked for and sutured.

The dangers to the fetus are trauma, compression of the brain, and tentorial tearing caused by too strong compression and traction. Fracture of the fetal skull and facial paresis may occur if the forceps has been incorrectly applied and compresses the nerve where it nerve emerges in front of the mastoid process.

Vacuum extractor or ventouse

The vacuum extractor, or ventouse, consists of a cup, either metal or plastic (the ‘soft cup’) with a handle. The cup is attached to a tube, which connects with the suction apparatus. The cup is positioned over the flexion point of the head, which is located along the sagittal suture 3 cm from the posterior fontanelle of the fetal head, and is held firmly against the scalp while a vacuum is slowly built up. This sucks some of the scalp into the cup, forming a firm attachment. Once a vacuum of 0.8 kg/cm2 is obtained, the perimeter of the cup is checked to ensure that no vaginal tissue is included and traction is applied by pulling the handle at right-angles to the pelvic curve, concurrently with a uterine contraction and with the mother’s own expulsive efforts.

If the head is in a transverse or posterior position a manoeuvrable cup, such as the Bird posterior cup or the Omnicup (Fig. 24.16), is used as it allows accurate placement over the flexion point.

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Fig. 24.16 Omnicup vacuum extractor system. Note that the vacuum tubing is attached to the side of the cup, which allows the cup to be placed over the flexion point in deflexed (occipitoposterior and lateral) positions, enabling rotation of the fetal head as it descends. The system incorporates a palm pump.

The hard cups (e.g. Malmstrom, Bird, O’Neil and Omnicup) have a lower failure rate than the soft cups (e.g. Silc, Silastic) – 5% versus 14% – and a lower detachment rate, 13% versus 33%.

Systematic reviews comparing the vacuum extractor with forceps delivery have concluded that the vacuum extractor:

• Is less likely to deliver the baby
• Is associated with a lower caesarean section rate
• Is less likely to cause serious maternal injury
• Requires less anaesthesia, both regional and local
• Is associated with less maternal pain at delivery and at 24 hours
• Is associated with more cephalhaematomas, subgaleal haemorrhage and retinal haemorrhages
• Is not associated with significant differences in neonatal morbidity
• Results in more maternal concerns about the appearance of the baby.

The ventouse cannot be used to aid the delivery of the aftercoming head of a breech presentation, or if the baby is preterm. Early reports suggested that it should not be used after fetal scalp blood sampling, but larger reviews have not supported this. The most serious injury associated with vacuum extraction is a subgaleal (subaponeurotic) haemorrhage. This almost always follows poor application of the cup, prolonged extraction, and multiple cup detachments and reapplications. It is important that all babies delivered by vacuum extraction or forceps are carefully examined after delivery and monitored at regular intervals if the delivery was difficult.

CAESAREAN SECTION

Caesarean section means that the baby is removed from an intact uterus by abdominal operation. In many developed countries the caesarean section rate has risen from 5% 30 years ago, to 15–35%. This increase is due to:

• Fashion
• Fear of litigation if a perfect baby is not born
• The changing pattern of conception: women are delaying the conception of their first child and are limiting the number of children they have
• The trend to deliver all breeches and a high proportion of multiple pregnancies abdominally.

Indications for caesarean section

These have broadened in recent years and are listed in Box 24.1.

Box 24.1 Indications for caesarean section

• Failure of labour to progress (dystocia)

abnormal uterine action
cephalopelvic disproportion

• Malpresentation or malpositions

breech
face and brow
transverse lie
occipitoposterior
prolapse of umbilical cord
multiple pregnancy

• Antepartum haemorrhage

abrupto placentae
placenta praevia

• Hypertensive disease in pregnancy
• Diabetes mellitus
• Fetal conditions

fetal distress
isoimmunization
very low birthweight

• Older primigravidae
• Failed induction of labour
• Repeat caesarean section

Technique of caesarean section

There are two types of caesarean section. In the first, a transverse incision is made through the stretched lower uterine segment. In the second – the classic section – a vertical incision is made through the myometrium. The classic section is now rarely used, except when the lower uterine segment is excessively vascular, cannot be reached because of extensive adhesions, or if the fetus presents as a transverse lie, with an impacted shoulder. Caesarean hysterectomy may be required if intractable bleeding occurs, for placenta accreta, or if the uterus has ruptured.

The operative technique is shown in Figure 24.17. As blood loss is unpredictable, cross-matched blood should be available.

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Fig. 24.17 The technique of caesarean section. (A) and (B) The loose peritoneum covering the lower uterine segment is divided and pushed down. (C) The exposed muscle of the lower segment is incised so that the membranes bulge into the wound. The incision may be extended with a knife, or the muscle fibres separated with the fingers. (D) The membranes are ruptured and the head delivered using a forceps blade as an inclined plane, counterpressure being exerted on the fundus. (E) The placenta has been expelled and the wound sutured in layers. Great care must be taken at the angles.

Postoperative care is no different from that for any other abdominal operation. Early ambulation is encouraged, especially as in some hospitals the neonate is kept in the nursery for 24–48 hours. Maternal morbidity varies between 3 and 12%, depending on the reason for the caesarean section. Endometritis accounts for two-thirds of morbidity. For this reason, prophylactic antibiotics are routinely given during the operation. Women at higher risk of developing thromboembolism are prescribed prophylactic anticoagulants.

Caesarean section is a very safe operation, the overall mortality rate being about 0.4 per 1000 sections and 0.1 per 1000 sections performed electively.

VAGINAL BIRTH AFTER PREVIOUS CAESAREAN SECTION

When a caesarean section is performed for a non-recurrent condition, the next baby may be born vaginally or by caes-arean section depending on the wishes of the woman and the advice of the obstetrician. Studies from countries outside North America show that nearly half the women who had a previous caesarean section deliver their next baby vaginally. In North America less than one-third deliver vaginally. The expected rate for achieving a vaginal birth is between 60 to 80%. This is reduced by about 10% if labour is induced and for women with a BMI >30 the success rate is 55%.

If a woman chooses a vaginal birth after a caesarean section (VBAC), the birth should take place in a well-equipped hospital staffed by experienced obstetricians. The reason for this is that the trial of vaginal delivery is terminated by caesarean section in one-fifth of all cases, 0.25% of women suffering a ruptured uterus. Induction of labour using prostaglandins is associated with an increased risk of uterine rupture by comparison with ARM and Syntocinon and therefore should be used only with close supervision.

If an elective caesarean section is chosen, the maturity of the fetus must be established so that the operation is performed when the gestation period is greater than 38 weeks, to obtain the lowest neonatal respiratory morbidity.

VERSION

External cephalic version may be chosen when a fetus presenting as a breech has not turned cephalically by the 37th week of pregnancy. Before attempting the version the doctor must be sure that the pelvis has normal dimensions and that the placenta is not praevia. The mother should not have hypertension or a multiple pregnancy.

Some doctors give a tocolytic drug intravenously before the attempt. The version is performed gently. The breech is mobilized and the version attempted by lifting it with one hand and pushing the fetal head down with the other (Fig. 24.18). The fetal heart rate is either monitored continuously or every 2 minutes during, and for 30 minutes after, the version. If the fetal heart rate falls below 90 bpm during the version, the attempt is abandoned. Short-term bradycardia occurs in 20% but delivery by emergency caesarean section, because of persistent bradycardia, is required in only 0.2%.

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Fig. 24.18 External version. The obstetrician has lifted the buttocks out of the pelvis; his right thumb controls the baby’s head and the direction in which the child is moved encourages flexion.

Other problems associated with version are uncommon. They include rupture of the membranes, cord entanglement around a limb of the fetus, and the onset of premature labour.

There is insufficient evidence to support moxibustion (burning of Artemisia vulgaris to stimulate acupuncture point lateral to the small toe), acupuncture alone or maternal postural positioning, to effect conversion of the breech to a cephalic presentation.

Internal podalic version, in which the doctor’s hand is introduced into the uterus to grasp a limb and pull it through a fully dilated cervix, is rarely performed today. It may find use in cases of the delayed birth of a second twin which is lying transversely in the uterus, but in most cases caesarean section is safer.

DESTRUCTIVE OPERATIONS ON THE FETUS

There is very little place for these procedures in modern obstetric practice. An exception may be when a hydrocephalic fetus has died during labour. In this case the head is perforated with a perforator and the fluid allowed to drain, making the fetus easier to deliver.

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