On Twins: ‘It is a constant rule, to keep patients, who have born one child, ignorant of there being another, as long as it can possibly be done’.
Thomas Denman
An Introduction to the Practice of Midwifery. London: J. Johnston, 1795
The second twin is at increased risk during delivery because of malpresentation and placental separation following delivery of the first. A multicentre randomized controlled trial, the Twin Birth Study, has confirmed the safety of vaginal birth in experienced hands. Thus, once again the skills of the obstetric accoucher will be paramount, just as they were when the first edition of this book was published in 1908.
Obstetric Factors
Malpresentations
In 60% of twin pregnancies one or both of the twins is non-vertex at the time of delivery; however, the first twin is cephalic in 75−80% of cases. The most common combinations are vertex/vertex (40%), vertex/non-vertex (35–40%) and non-vertex/other (20–25%). The main factor in considering the planned delivery method is the presentation of the first twin. The presentation of the second twin should not be relevant in the decision of the route of delivery, because in about 20% the second twin changes presentation after the first twin has been delivered.
Second Twin
The second twin is at increased risk during labour and delivery for two reasons:
- 1.
Placental separation, which reduces oxygen transfer leading to asphyxia. The longer the interval following delivery of the first twin the higher the risk of caesarean delivery for the second twin and the potential for asphyxia (see below).
- 2.
Malpresentation and thus vulnerablity to trauma associated with intrauterine manipulations. Some have sought to apply the findings of the Term Breech Trial to the second twin in breech presentation. However, the presentation of the second twin was not related to the risk of adverse outcome in the Twin Birth Study. Furthermore, internal version and breech extraction has been shown to result in a lower incidence of caesarean delivery for the second twin compared to those delivered following external cephalic version.
Individual Considerations
In each case a number of factors will influence the decision for or against labour and vaginal delivery:
- •
General maternal considerations such as age, parity, infertility and medical complications.
- •
Potential fetal compromise including fetal growth restriction and abnormal tests of fetal wellbeing are more frequent in twins, and will often lead to delivery by caesarean section.
- •
Estimated fetal weight. Although there is no evidence to support planned caesarean section for low birth weight twins, many obstetricians will choose this route for those infants less than 32 weeks’ gestation or with an estimated fetal weight < 1500 g.
- •
Weight discrepancy. Significant weight discrepancy (> 750 g), particularly if twin B is bigger than twin A, is often used as a reason for caesarean delivery. However, the reproductive history of the mother is relevant; for example, a multiparous woman with previous large babies is unlikely to run into complication at delivery of twin infants, who are usually significantly smaller, even if the second twin is larger than the first.
- •
Monoamniotic twins are rare but the risk of cord entanglement is high enough to warrant elective caesarean delivery.
- •
Appropriate facilities and skilled personnel should be available. This involves an obstetrician, anaesthetist and neonatal personnel plus sufficient equipment for two infants.
Maternal Risks
Mothers of twins have a higher risk of maternal morbidity and mortality than singletons. The reasons include a higher incidence of anaemia, hypertension and pre-eclampsia, gestational diabetes, postpartum haemorrhage and thromboembolism. In addition, with the high incidence of preterm labour the mother is exposed to the potential risks of tocolytic therapy (see Chapter 9 ).
Anaesthetic Factors
Epidural anaesthesia is the analgesic of choice, although for uncomplicated twin delivery inhalation analgesia and pudendal block may be adequate. Less narcotic analgesia is desirable in the preterm fetus and, should intrauterine manipulation or caesarean delivery become necessary, the mother is saved the hazards of rapid induction of general anaesthesia. The anaesthetist should be prepared to provide rapid uterine relaxation with intravenous nitroglycerine (see Chapter 28 ).
First Stage of Labour
Currently most authorities recommend induction between 37 and 39 weeks if spontaneous labour does not occur, due to an increase in the stillbirth rate that occurs after this gestation . The first stage of labour is managed as a singleton; however, an intravenous infusion should be established. If the presentation of twin A is other than cephalic, caesarean section is usually advisable. Induction of labour and augmentation with oxytocin is used as for a singleton. Both twins should have electronic fetal heart rate monitoring (EFM). Care should be taken that each fetus has a distinct fetal heart rate pattern. The author has seen several cases in which the same twin was inadvertently monitored, leaving asphyxia undetected. Ideally, a fetal scalp clip should be applied to twin A as soon as possible and twin B monitored externally.
Second Stage of Labour
The necessary anaesthetic, obstetric and neonatal equipment and personnel should be marshalled and the second stage of labour conducted in the operating room. In general the first twin is delivered spontaneously or assisted by forceps or vacuum for the same indications as a singleton. Once delivered, the cord of the first twin should be clamped and ‘tagged’ and, because there is usually a period of uterine inertia, one should have prepared a solution of oxytocin to ‘piggy back’ onto the main intravenous line.
‘Being convinced there is a second child, the membranes must be immediately broke without waiting for pains; and introducing the hand into the womb, to find out the feet, the child must be brought forth by them’.
Fielding Ould
A Treatise of Midwifry. Dublin: O. Nelson, 1742, p52
Delivery of the Second Twin
Once the first twin has been delivered, the lie of the second twin should be established. Ultrasound may help delineate the lie; however, abdominal palpation and vaginal examination will usually confirm the presentation. The following protocol is suggested:
- •
Continuous EFM should be established.
- •
If the presentation is cephalic check vaginally to rule out cord presentation, which can also be seen on ultrasound.
- •
Provided there is no cord, steady the presenting part over the pelvic brim, rupture the membranes and apply the internal scalp electrode. The oxytocin infusion can then be started as needed.
- •
Provided the fetal heart rate is normal one can wait for spontaneous delivery of the second twin – either cephalic or an assisted breech delivery (see Chapter 16 ).
- •
If the second twin is an oblique or transverse lie and the obstetrician is trained in the procedure then a breech extraction with or without internal podalic version should be performed (see Chapters 16 and Chapter 28 ). If the obstetrician is skilled at this procedure and there is good anaesthesia and uterine relaxation this is the method of choice and attended by good results.
- •
For those not trained in the above, external cephalic version may be attempted ( Fig 17-1 ) (see Chapter 28 ).
