Abnormal fetal presentations

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Chapter 21 Abnormal fetal presentations

Abnormal presentations include, in order of frequency, occipitoposterior presentations, breech presentations, face presentations, transverse presentations and brow presentations.

OCCIPITOPOSTERIOR PRESENTATIONS

In about 10% of pregnancies the fetal head enters the maternal pelvis with its occiput in one of the posterior segments of the pelvis (see Fig. 8.4, p. 70).

The diagnosis may be made on abdominal palpation when the fetal back is felt in one of the mother’s flanks, the fetal heart being loudest here (Fig. 21.1). In labour, vaginal examination provides more information, the occiput and the anterior fontanelle being identified (Fig. 21.2).

Fig. 21.1 Occipitoposterior position – abdominal findings.

Fig. 21.2 Possible modes of rotation of the head.

During labour the fetal head is forced deeper into the pelvis, and usually flexes on the fetal neck. Once full dilatation of the cervix has occurred its progress may be in one of three ways (Fig. 21.2):

• In 65% of cases the head rotates through 135° so that the occiput lies behind the symphysis pubis.

• In 20% of cases rotation of the fetal head ceases and it becomes arrested in a transverse diameter of the pelvis.

• In 15% of cases the fetal head rotates posteriorly.

Thus, in most cases the fetal head undergoes a long or a short rotation (Fig. 21.3).

Fig. 21.3 Occipitoposterior. Long rotation (A–D); short rotation (E–H).

Management of occipitoposterior presentations

There is no proven management that encourages rotation to an occipitoanterior position before labour starts. Once begun, the duration of labour tends to be longer in occipitoposterior positions and the mother requires more support, analgesia and hydration. Progress is monitored using a partogram. The descent of the head, and its position, are checked regularly. Any marked delay in the first stage of labour leads to prolonged labour (see p. 178–179) and a decision has to be made whether to continue or to perform a caesarean section. Delay in the second stage of labour of more than 1.5–2 hours’ duration indicates the need for help to deliver the baby. If the fetal head undergoes the long rotation a spontaneous vaginal delivery may be expected. This occurs in 65% of cases. If the fetal head undergoes the short rotation and descends to the pelvic floor in the posterior position, the infant may be born spontaneously (8% of all cases) or may need help by forceps or vacuum (7%). On the other hand, the fetus may not descend much beyond the ischial spines and a manual rotation and forceps delivery, Kjelland’s forceps delivery or vacuum extraction may be necessary (see Ch. 22). These procedures are also required if the fetal head arrests in a transverse diameter of the pelvis. Between 5 and 10% of babies who are occipitoposterior are delivered by caesarean section.

BREECH PRESENTATIONS

The frequency of breech presentation falls as pregnancy advances. At the 30th week of pregnancy 15% of fetuses present as a breech; by the 35th week the proportion has fallen to 6%, and by term only 3% present as a breech. Most of these babies spontaneously turn to become cephalic. If the presentation is still a breech at the 37th week many obstetricians attempt a cephalic version, which is described on pages 197–199. Version is easier if the fetus has flexed legs, one of the three types of breech presentation (Fig. 21.4).

Fig. 21.4 Types of breech presentation. (A) Breech with extended legs (frank); (B) breech with flexed legs (complete); (C) footling.

The presentation of the fetus is of no clinical importance before the 32nd–35th weeks. At this stage of pregnancy the diagnosis of a breech presentation is made by finding, on palpation, that the lower pole of the uterus is occupied by a soft, irregular mass and that in the fundal area a firm, smooth, rounded mass is present which bounces between the fingers if gently pushed. On auscultation the fetal heartbeat is loudest above the umbilicus. If any doubt remains after palpation and a vaginal examination, an ultrasound image will clarify the diagnosis and will exclude fetal malformations.

The fetus may be left as a breech or an external cephalic version may be attempted at 36–37 weeks of gestation, depending on local custom.

Problems with breech presentations

Few problems occur during pregnancy, although some expectant mothers complain of pressure beneath the diaphragm. Because breech births frequently require operative delivery there is an increased risk to the fetus, which is minimized by skilled attention and decision-making. In the absence of any other complications of pregnancy, preterm breech births (weight < 2500 g) carry a mortality of 12%, as do large postmature babies (weight > 3500 g). Mature fetuses whose weight is in the normal range have a mortality of 1%.

The main causes of morbidity are intracranial haemorrhage, asphyxia and fracture of the humerus, femur or clavicle.

Management of breech births

Elective caesarean section at term

The Term Breech Trial reported that in developed countries delivery by caesarean section was the safest option for the baby with a reduction in the perinatal mortality from 1.15 to 0.6%, and consequently few fetuses presenting as a breech are now electively delivered vaginally. It is noteworthy that at 2 years of age there was no difference in the development between those delivered vaginally or by caesarean section

Vaginal breech birth

It is still important to understand the management and the mechanism of a breech birth, as an unexpected breech presentation may occur at full cervical dilatation with insufficient time to organize a caesarean section. This is shown in Figures 21.5–21.14 and is described in the captions.

Fig. 21.5 The breech is presenting as a right sacroanterior. The bitrochanteric diameter of the buttocks has entered the pelvis in the transverse diameter of the pelvic brim. With full dilatation of the cervix, the buttocks descend deeply into the pelvis.

Fig. 21.6 When the buttocks reach the pelvic floor, the pelvic ‘gutter’ causes the buttocks to rotate internally so that the bitrochanteric diameter lies in the anteroposterior diameter of the pelvic outlet.

Fig. 21.7 The anterior buttock appears at the vulva. With further uterine contractions the buttocks distend the vaginal outlet. Lateral flexion of the fetal trunk takes place and the shoulders rotate so that they may enter the pelvis. At this stage the attending doctor or nurse–midwife has donned gown and gloves and is prepared to aid the delivery.

Fig. 21.8 If the buttocks make no advance during the next several contractions, an episiotomy is made and the buttocks are born by groin traction.

Fig. 21.9 The buttocks have been born and the shoulders have entered the pelvis in its transverse diameter. This causes the external rotation of the buttocks so that the fetal back becomes uppermost.

Fig. 21.10 If the fetus has extended legs, the attendant may have to slip a hand along the anterior leg of the fetus and deliver it by flexion and abduction, so that the rest of the birth may proceed.

Fig. 21.11 The fetal shoulders have reached the pelvic ‘gutter’ and have rotated internally so that the bisacromial diameter lies in the anteroposterior diameter of the outlet. Simultaneously, the buttocks have rotated anteriorly through 90°. The fetal head is now entering the pelvic brim, its sagittal suture lying in the brim’s transverse diameter. Descent into the pelvis occurs with flexion of the fetal head.

Fig. 21.12 The baby has been born to beyond its umbilicus. A loop of umbilical cord is pulled down to make sure that it is not holding back the birth. Gentle traction downwards and backwards is made by the attendant, so that the anterior shoulder and arm are born. The baby is now lifted upwards in a circle so that the posterior shoulder and arm may be born. Sometimes one arm is extended and has to be dislodged downwards. The procedure requires skill, otherwise a fractured clavicle or humerus may result. Once the anterior arm has been born, the baby’s body and the posterior arm are freed in a similar manner.

Fig. 21.13 (A) The baby hangs unsupported from the mother’s vulva. The doctor applies slight suprapubic pressure to encourage further flexion of the head. When the nape of the baby’s neck has appeared, the attendant holds the baby by the feet and swings it upwards through an arc. (B) This manoeuvre, by using the lower border of the sacrum, pulls the head down and rotates it through the pelvic outlet so that the chin, nose and forehead appear.

Fig. 21.14 An alternative is to deliver the fetal head by forceps.

An algorithm for the management of breech presentations

Figure 21.15 presents an algorithm for the management of breech presentations. Not included is breech extraction, as in such cases the baby is delivered by the doctor. The main use of breech extraction is for the birth of a second twin, or if the breech is impacted in the midpelvic cavity. Unless the obstetrician is very skilled, caesarean section is safer.

Fig. 21.15 Management of breech presentations. If detected at 36 weeks confirm gestation period by checking date of last menstrual period, visits during pregnancy and ultrasound examination. Attempt external cephalic version (ECV) without anaesthesia, using tocolytics and real-time ultrasound. If ECV fails, wait for labour.

TRANSVERSE LIES, OBLIQUE LIES AND SHOULDER PRESENTATIONS

Shoulder presentations, unstable lie, transverse lie and oblique lie may be detected in late pregnancy. These conditions occur in 1 in 200 births, usually in multiparous women. The aetiology is varied. They may occur in a lax multiparous uterus with no other complication of pregnancy, but may be associated with polyhydramnios, placenta praevia or a uterine malformation (see Fig. 36.4, p. 280). An ultrasound examination is helpful in excluding placenta praevia.

The diagnosis is made by finding a broad asymmetrical uterus with a firm, ballottable round head in one iliac fossa and a softer mass in the other (Fig. 21.16).

Fig. 21.16 Transverse lie.

Management in pregnancy

When placenta praevia has been excluded a gentle cephalic version may be attempted, but in many cases the fetus returns after some time to its previous presentation. If the lie remains unstable, the expectant mother should be advised to report to hospital immediately labour starts or, if the social conditions are unfavourable, may be admitted to hospital to await labour. In some cases the presentation is corrected to cephalic and the head is held over the brim. The membranes are then ruptured and the head pressed into the pelvis as the liquor amnii is released.

Another choice is to perform an elective caesarean section.

Management in labour

If the shoulder presentation is not detected until labour has been established, caesarean section is the preferred option.

FACE PRESENTATIONS

Face presentation occurs in 1 in 500 births, usually by chance, but in 15% of cases the baby is anencephalic, or has a tumour of the neck or shortening of the neck muscles.

Face presentation is rarely diagnosed before labour, and even then may be missed until a face with swollen, distorted lips appears at the vulva. Abdominal palpation may reveal a peculiar S-shaped fetus with feet on the opposite side to the prominent occiput. The fetal head has not usually entered the pelvis (Fig. 21.17).

Fig. 21.17 Abdominal palpation in face presentation.

Vaginal examination during labour may clarify the presentation (Fig. 21.18), but in late labour, when much facial oedema has occurred, a breech may be misdiagnosed.

Fig. 21.18 Touch picture of the face.

Mechanism and management of labour

In most cases the face enters the transverse diameter of the pelvis with the fetal chin in a mentotransverse position. Descent into the pelvis is delayed until late in the first stage or the second stage of labour (Fig. 21.19). Rotation usually occurs anteriorly so that the chin lies behind the pubis, and delivery occurs spontaneously by flexion of the head or may be aided by forceps. In a few cases the fetal chin rotates posteriorly, impacting the fetal head and preventing vaginal delivery. The impacted fetal head may be rotated using Kjelland’s forceps or, preferably, the fetus may be delivered by caesarean section.

Fig. 21.19 Diagram of engagement. In the face presentation engagement occurs late, as the parietal prominences do not enter the brim until the face has reached the pelvic floor.

BROW PRESENTATIONS

Brow presentation is the most unfavourable and the least common (1 in 1500 births) of all malpositions and malpresentations. It may occur during late pregnancy (when it usually converts into a cephalic presentation). An ultrasound examination should be made to exclude fetal malformations, particularly hydrocephaly.

The patient should be seen each week to check the presentation, and told to come into hospital as soon as contractions start or the membranes rupture.

In labour, brow presentation is diagnosed when the fetal head is high and a sulcus can be identified between the head and the back.

Treatment consists of caesarean section, unless the baby is grossly abnormal or dead, when a destructive operation may be chosen (see p. 199).

MULTIPLE PREGNANCY

Multiple pregnancy occurs when two or more ova are released and fertilized (dizygotic, DZ) or when a single fertilized ovum divides early to form two identical embryos at the inner cell mass stage or earlier (monozygotic, MZ). The incidence of twins is 1 in 90 pregnancies and that of triplets is 1 in 90 × 90 (8100) pregnancies. DZ twins are more common in older mothers, with increasing parity and where there is a maternal family history of twins. They are more common in women of African origin and less common in Asian races. Since the introduction of assisted reproductive technology, the incidence of multiple pregnancies has increased and in developed countries accounts for 50% or more of multiple pregnancies. Ultrasound examination in early pregnancy has also identified more twins, but in half of those identified one fetus dies and disappears before the second half of pregnancy – the so-called vanishing twin. This occurs in 20–50% of twins, 50% of triplets and 65% of quadruplets.

In DZ multiple pregnancy each fetus is a separate individual with its own placenta, amnion and chorion. In MZ multiple pregnancy the two fetuses have a single placenta and chorion; 98% of MZ twins have their own amniotic sac (MZ diamniotic), but for the 2% who are monoamniotic this carries a high risk of cord entanglement. As there is vascular communication between the two parts of the placenta in over 75% of MZ twins it is not unusual for one twin to obtain a reduced supply of nutrients and grow more slowly than the other. In up to 35% this can cause twin-to-twin transfusion, which may result in acute polyhydramnios, anaemia, oligohydramnios and severe growth restriction in the donor, and polycythaemia, hypervolaemia, cardiac failure and polyhydramnios in the recipient twin. Occasionally one fetus dies early in pregnancy and becomes mummified (fetus papyraceous).

Because of the greater demands for nutrients, a fetus in a multiple pregnancy tends to be smaller than a singleton fetus, as its growth in utero is slower (Fig. 21.20).

Fig. 21.20 The intra-uterine growth of multiple and single pregnancies as assessed by ultrasound fetometry.

Diagnosis of multiple pregnancy

Few multiple pregnancies are diagnosed in the first half of pregnancy except by ultrasound scanning. Because virtually every woman has a scan at least by 18–20 weeks’ gestation it is now rare for a multiple pregnancy not to be diagnosed before it becomes clinically evident. In those rare situations when a scan has not been performed by the second half of pregnancy, a multiple pregnancy can be suspected if:

• The abdominal girth and uterine size are greater than expected from the period of amenorrhoea.

• Palpation shows an excess of fetal parts, and two fetal heads can be detected.

Management of multiple pregnancy

Compared with a singleton pregnancy, a multiple pregnancy is likely to be associated with more complications (Table 21.1). For this reason the expectant mother requires additional antenatal care. She should be seen at 2-weekly intervals from the time of diagnosis. Maternal anaemia should be sought and treated, and there is a strong argument for insisting that the patient takes folic acid 4 mg and an iron salt each day. When a woman carrying twins goes into preterm labour, the decision whether to deliver the twins by caesarean section or to attempt a vaginal birth has to be made. A problem is that in 20% of twin pregnancies the weight of one twin is 20% less than that of the other. There is no consensus about the safest method to use.

Table 21.1 Complications of pregnancy in singleton and multiple pregnancies

Complication	Singleton (%)	Twin (%)
Hypertensive disorders	5	15
Anaemia	3–5	15
Polyhydramnios	2	12
Intra-uterine growth restriction	10	25–33
Congenital anomalies	2–4	4–8
Preterm birth	5	40

A woman carrying a multiple pregnancy has an increased blood volume and an extra burden on her cardiovascular system. It is common practice to monitor fetal growth by ultrasound every 2–3 weeks from the 30th week. This is especially important in MZ twins so that twin-to-twin transfusion can be detected early. Laser ablation of the communicating placental vessels substantially improves the likelihood of a successful outcome. If growth ceases and/or Doppler blood flow indices are abnormal, delivery is expedited. The rising perinatal mortality and morbidity with increasing gestation (the nadir for mortality being 37 weeks) has led to the practice in a number of centres of electively delivering all twin pregnancies by 37–38 weeks.

Higher-multiple pregnancies

Since the development of assisted reproductive technology, the prevalence of multiple pregnancies has increased. A number of these will be triplets or higher. The perinatal mortality of these fetuses and neonates is high. To manage this problem, selective termination of some or all fetuses, by intracardiac injection, has been used. The associated medical and legal issues have not been resolved.

Triplets have an 80% risk of preterm delivery. The trend is to deliver triplets and quadruplets by caesarean section.

Management in labour

The position of the leading fetus should be checked on admission. In 45% of twin pregnancies both fetuses present as cephalic; in 25% as cephalic and breech; and as breech and cephalic or breech and breech in 10% each. If the first twin presents transversely, caesarean section is the preferable approach. If the first twin presents as a breech it is common practice (as yet unsupported by high-level evidence) to perform a caesarean section. In other cases a vaginal birth may be expected. The management of the labour is conducted in the way already described (Ch. 8). When the membranes rupture a vaginal examination is performed to check whether the umbilical cord has prolapsed.

The first baby is usually born without difficulty, if necessary following an episiotomy. Immediately following the birth, the doctor makes an abdominal examination to determine the lie and presentation of the second twin. If it is transverse, the doctor may attempt external version to bring the fetus into a longitudinal position. A vaginal examination is then made to confirm the presentation, and if it is longitudinal the second amniotic sac is ruptured artificially. The fetal presenting part is led into the pelvis. A second twin which remains in the transverse presentation should be delivered either by caesarean section or by internal podalic version, depending on the skill of the obstetrician.

Following the birth of the first twin, uterine contractions may diminish for a few minutes. If they do not return soon, an intravenous oxytocin infusion may be set up. The birth of the second twin is usually uncomplicated, but postpartum haemorrhage may be expected and should be anticipated by managing the third stage actively.

Risk to mother and fetuses

There is no increased risk to a mother who has received appropriate antenatal care. The risk to a fetus of a multiple pregnancy is higher than to a singleton, mainly because of the increased incidence of preterm birth. The perinatal mortality of twin births is 50 per 1000, five times that of a singleton birth. The death of one of the twins during the birth, or in the neonatal period, presents the parents with unique problems, as they have to adjust to having one living baby who no longer has a same-age sibling. The incidence of cerebral palsy increases with the number of fetuses being 4–5 times greater in twins and 17 times in triplets and quadruplets compared with singletons.

Psychological effects of twins on the parents

The knowledge that she is carrying twins may have a considerable psychological effect on the mother and her partner, and the attending health professional needs to help and counsel the couple. If the multiple pregnancy was diagnosed in the early weeks by ultrasound scanning, the first matter to be discussed is the problem of the ‘vanishing twin’. After the 20th week of pregnancy the woman and her partner should be made aware that there is a higher chance of developing complications that may require admission to hospital and which may lead to a premature birth. If the woman already has a child, or children, her absence from the home may require help from partner or relatives, and studies have shown that she has an increased chance of developing depression in late pregnancy. She also has a greater chance that the birth will be by caesarean section, which may cause anxiety, and the issue should be discussed.

In the postnatal period the demands of caring for two small babies adds to the problem of adjusting to parenthood (see p. 92–93), and usually means that the couple have little time to be with each other to enhance their general and their sexual relationship. In the period after childbirth, more women who have given birth to twins report anxiety and depression and often need support and help. Women report that discussion of these matters during pregnancy and the availability of support both during and after pregnancy reduce the stress of having twins. Fortunately, in the community there are self-help groups whose support and counselling are invaluable. However, the doctor or nurse attending the woman during and after pregnancy should be aware of the problems and of the need to talk with the woman and her partner.