Twin and Triplet Delivery

Malpresentations

In 60% of twin pregnancies, one or both of the twins is nonvertex 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/nonvertex (35–40%) and nonvertex/other (20–25%). The main factors in considering the planned delivery method include the presentation of the first twin, gestational age, presence of growth restriction in either fetus, and maternal factors or morbidity, which may contraindicate vaginal birth. The presentation of the second twin should not be relevant in the decision of the route of delivery, because in about 15–20% of cases the presentation of the second twin changes after the delivery of the first twin. This has been shown to be more likely to occur in parous women, when the gestational age is less than 34 weeks, and in cases where antenatal ultrasound scan had demonstrated changes in the presentation of the second twin. Furthermore, such changes in the presentation of the second twin dramatically increases the chance of caesarean delivery of the second twin, presumably more so in inexperienced hands.

Second Twin

The second twin is at increased risk of compromise during labour and delivery for a number of reasons:

• 1.

  The second twin may be smaller with less reserve than the first twin and is sometimes more difficult to monitor, particularly in situations of maternal obesity, even with an internal electrode attached to the first twin. The fetal heart rate (FHR) tracings may contaminate one another, or the transducers may monitor the baby and obscure or fail to detect FHR abnormalities in a twin. This problem is overcome by a technical feature, which allows the separation of the traces in modern machines. Even so, cases still occur in which the same twin was inadvertently monitored, leaving asphyxia undetected.

• 2.

  During normal vaginal twin delivery, the umbilical cord gas status of both the first and the second twins deteriorated in line with the duration of their corresponding second stage; however, the effects are greater in the second twin and unrelated to the duration of the first twins’ second stage, suggesting a diminished uteroplacental exchange function after the delivery of the first twin. This may be related to placental separation, or reduced uteroplacental blood flow as a result of retraction of the uterine muscle, which may reduce oxygen transfer to the fetus, leading to asphyxia. Therefore, close monitoring and expeditious delivery of the second twin, if required, are important aspects of the management of the second twin. The practitioner should appreciate that the longer the interval following delivery of the first twin, the higher the risk of asphyxia and caesarean delivery for the second twin even in the presence of close FHR monitoring.

• 3.

  Malpresentation and thus vulnerability to trauma and cord accidents 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 with 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. These factors may be social or related to parental choice and not necessarily clinical:

• General maternal considerations including age, choice, parity, history of subfertility, and medical complications.

• Potential or actual evidence of fetal compromise, including fetal growth restriction. 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 ≥20% or >750 g, particularly if the second twin is bigger than the first, 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.

• Chorionicity. Some fetal medicine twin experts advocated elective caesarean delivery for all monochorionic twins in the past, for fear of acute peripartum twin-to-twin transfusion syndrome (TTTS). However, the numerical risk of this event is small (<2%) and although there is no strong evidence to date to recommend this approach, the practice is still adopted in some settings. Vaginal delivery is a safe and acceptable mode of delivery for uncomplicated monochorionic diamniotic twins after 34 completed weeks of gestation. 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. These include a delivery room with adequate space for personnel and equipment for two infants, an obstetrician, anaesthetist and neonatal personnel. In some centres, all twin deliveries are conducted in theatre. In the absence of a complication or where one is anticipated, this is not our practice. Furthermore, it may promote operative interventions by lowering the threshold at which clinicians are likely to intervene, given that they are already in the operating theatre.