The incidence of multiple pregnancy has increased owing to an increase in assisted conception programmes, although twins, triplets and quadruplets also occur naturally. The natural incidence of twins is 1 in 80 pregnancies, triplets 1 in 8000 and quadruplets 1 in 800,000. The obstetric anaesthetist has an important part to play in the management of these deliveries.
Problems and special considerations
The mother carrying a multiple pregnancy experiences all the minor pregnancy complaints in excess. She will be more likely to be very uncomfortable and to suffer from backache, heartburn and varicose veins. Often she will be dyspnoeic at rest or on minor exertion, and she may be unable to lie on her back because of supine hypotension, which may be difficult to relieve except in the full lateral position. She is also more prone to the following risks:
• Anaemia (real and dilutional)
• Pregnancy-induced hypertension
• Gestational diabetes
• Fetal growth restriction
• Malpresentations, including of the second twin after delivery of the first twin
• Premature labour
• Prolonged labour
• Operative interventions for delivery
• Postpartum haemorrhage (because of uterine atony and the large placental site)
• More technically challenging electronic fetal heart rate monitoring
• Intrauterine death
Management options
Many twins and nearly all triplets and quadruplets are booked for delivery by elective caesarean section, although because premature labour is more common, caesarean section is often performed as a non-elective procedure. The indications for twins to be delivered by elective caesarean section include malpresentation of the first twin, previous caesarean section, poor obstetric history (which may include assisted conception) and maternal request. Regional anaesthesia is considered preferable for caesarean section. Great care must be taken when performing regional anaesthesia in these women to ensure that supine hypotension is avoided. If general anaesthesia is required, the reduction in functional residual capacity secondary to the enlarged uterus may be greater than with singleton pregnancies, resulting in more rapid oxygen desaturation during apnoea.
Twins may be delivered vaginally, although the labour and delivery may not be straightforward and the above factors should be considered. Fetal heart monitoring should be reviewed frequently to ensure both babies are being monitored. Epidural analgesia is recommended; firstly it should provide excellent analgesia for what may be a long labour requiring oxytocic drugs, and secondly - and most importantly - the epidural can be used if there are problems with the second twin. It is important, therefore, to ensure that the epidural is working well throughout labour.
Approximately 40% of twins present vertex-vertex, a further 40% present vertex-non- vertex, and the remaining 20% present both non-vertex. Malpresentation of the second twin may require external or internal version and/or operative delivery, including caesarean section (which may be required urgently in approximately 5-10%, with 60% of all twin pregnancies being delivered by caesarean section). The anaesthetist should be present for the delivery of twins to ensure that the epidural block is adequate for these manipulations. Uterine relaxation with a tocolytic such as glyceryl trinitrate may be required to help facilitate intrauterine manipulation.
The second stage is usually conducted in the operating theatre. If caesarean section is indicated for the second twin, the anaesthetist must be able to extend the epidural block for the operation. Some anaesthetists advocate extending the epidural to produce a block suitable for caesarean section in all cases of twins, in case surgery is required. In rare instances, general anaesthesia may be required for the delivery of the second twin.
The oxytocin bolus must not be given until delivery of the second twin, and an infusion is particularly important post-delivery because of the increased risk of uterine atony.
Key points
• Women with multiple pregnancies are an ‘at-risk’ group.
• The anaesthetist should be actively involved with the care of these women, whether they are in labour or not.
• Special care is required to avoid aortocaval compression.
• There is increased likelihood of premature or prolonged labour, instrumental delivery and postpartum haemorrhage.
Further reading
Kilby MD, Bricker L; Royal College of Obstetricians and Gynaecologists. Management of monochorionic twin pregnancy. Green-top Guideline 51. BJOG 2016; 124: e1-45.
Melka S, Miller J, Fox NS. Labor and delivery of twin pregnancies. Obstet Gynecol Clin North Am 2017; 44: 645-54.
National Institute for Health and Care Excellence. Multiple Pregnancy: Antenatal Care for Twin and Triplet Pregnancies. Clinical Guideline 129. London: NICE, 2011. www.nice.org.uk/CG129 (accessed December 2018).