The risks associated with twin pregnancy are well described (2). The perinatal mortality rate for twins born by vaginal delivery is three to six times that for singleton pregnancies (3).
The increased perinatal morbidity and mortality relates in part to a high incidence of prematurity which affects over 50% of twins. The majority of these are between 32 and 38 weeks with approximately 10% below this age (1). Intracranial haemorrhage is a significant complication of prematurity. This occurs as a result of compression and traction on the soft cranial vault during its descent through the pelvis. It is a particular hazard of midcavity forceps delivery or breech extraction (4, 5). Another factor increasing perinatal morbidity is low birthweight, which, when corrected for age, is reduced by an average of 650g (1). In addition, there is a high incidence of malpresentation. The second twin presents breech in 41% of deliveries. The first twin presents breech in 17% (2). More rarely, the twins may be locked.
The second twin is acknowledged to carry the highest perinatal risk as a result of breech presentation and birth asphyxia. The latter may result from contraction or partial separation of the placenta after delivery of the first twin or a longer period during which the infant is subjected to the effects of aortocaval compression (Chapter 28). On the basis of this, it has become a general principle to minimise the second stage of delivery of the second twin (1, 2, 6).
Similarly, with triplets and quadruplets, the likelihood of malpresentation in the later fetuses increases, thus increasing the requirement for version and breech extraction - both of which procedures are associated with a high incidence of morbidity and mortality.
The likelihood of either instrumental or operative delivery in multiple pregnancies is recognised to be higher in than in singletons (2). Forceps may be applied electively to protect the premature head from a traumatic delivery. Following delivery of the first twin, version may be attempted to convert the second to a more favourable presentation. Pre-eclampsia (Chapter 40), placental abruption (Table E.3), vasa praevia and cord prolapse occur more commonly. Uterine distension contributes to the higher incidence of dysfunctional labour. Postpartum haemorrhage (Chapter 74) secondary to uterine atony is two to three times that seen with singleton pregnancies (7) (Table 74.1).
References:
1. Guttmacher AF, Schuyler GK The fetus of multiple gestations. Obstet Gynecol, 1958: 12:5 528 - 541.
2. James FM. Anesthetic Considerations for Breech or Twin Delivery. Clinics in Perinatology, 9:1 Feb, 1982 pp77 - 94.
3. Malinov AM, Ostheimer GW Anesthesia for the high risk parturient . Obstet Gynecol. 69:6, June 1987. pp951 - 964.
4. O'Driscoll K, Meagher D Traumatic intracranial haemorrhage in firstborn infants and delivery with obstetric forceps . British Journal of Obsterics and Gynaecology, 88:6, June 1987. 577-579.
5. Chiswick ML, James DK Kiellands forceps: association with neonatal morbidity and mortality . British Medical Journal, 6th Jan, 1979. 7-9.
6. Craft JB, Levinson G, Schnider SM Anaesthetic considerations in caesarean section for quadruplets. Canad Anaesth. Soc. J., 25:3, May 1978. 236-239.
7. Little WA, Friedman EA The twin delivery: Factors influencing second twin mortality - a review. Obstet. Gynecol. Surv. 1958 13:611