Perinatal death in twins
Authors: Philip Steer
Journal: BMJ (2007)

Twin pregnancies are becoming more common because of the increasing use of assisted reproduction technologies.1 They are associated with an eight to tenfold increase in the perinatal mortality rate,2 mainly because 40-70% of twins are born preterm.3 However, the safety of term vaginal delivery for twins has long been of concern; some large epidemiological studies have suggested that the second twin is at especially high risk of death.4 Complications associated with the second twin include the longer second stage, compound presentation leading to trauma during delivery, cord prolapse, and premature separation of the placenta.5 However, the only randomised controlled trial identified by a Cochrane review6 of caesarean section compared with vaginal delivery in twins7 and other small retrospective studies8 have not confirmed clinicians' subjective impressions of poor outcome in the second twin. 

The study by Smith and colleagues in this week's BMJ is welcome for the light it sheds on this topic.9 They studied twin pregnancies in the United Kingdom from 1994 to 2003 in which one of the twins died during or after labour for reasons other than congenital abnormality (1377 pregnancies). Before 37 weeks' of gestation, the two babies were at equal risk, but at term the risk of death was higher in second twins (odds ratio 2.3, 95% confidence interval 1.7 to 3.2, P<0.001). This was even more marked for deaths due to “intrapartum anoxia” or trauma (3.4, 2.2 to 5.3). Vaginally delivered second twins had a fourfold higher risk than first twins of death due to intrapartum anoxia. The authors suggest that these deaths might be prevented by planned elective caesarean section for all term twin pregnancies. Should this be adopted as routine practice?

Before recommending routine caesarean delivery to reduce risk to the baby, we must balance this against any potential increase in risk to the mother. The use of regional anaesthesia, prophylactic antibiotics, and thromboprophylaxis, plus improved suture materials and techniques for controlling haemorrhage have improved safety. Recently, a working party of the National Institutes of Health in the United States10 found no evidence that elective caesarean section increased risk to a healthy mother having her first delivery compared with planned vaginal birth. They highlighted that critics of high caesarean section rates often compare successful vaginal births with all caesareans, including those performed in an emergency during labour. The consensus group stated, “the evidence consistently indicates a lower risk of surgical complications in elective cesarean delivery than in unplanned cesarean delivery resulting from attempted vaginal delivery. Among planned vaginal delivery. . .there is a significantly higher rate of obstetric trauma than among planned cesarean delivery. The net direction of the evidence thus favors planned cesarean delivery.” 

Overall, caesarean section rates continue to rise across the globe11 and now exceed 25% in many places. In high and medium income countries, higher caesarean section rates are not associated with higher maternal mortality, and in low income countries, those with the highest caesarean section rates have the lowest levels of maternal and neonatal mortality.12 A large randomised trial of elective caesarean section for term breech presentation found a reduction in perinatal mortality of two thirds, with no increase in adverse outcomes in mothers.12 13 These findings rapidly changed practice in many countries, with beneficial results.14

In relation to twin pregnancies, in the UK obstetricians already seem to be voting with their scalpels. In the northwest London database of about 40 000 births each year, the overall proportion of caesarean sections in term pregnancies rose from 10.5% in 1988 to 20.8% in 2000. In parallel, the overall proportion of caesarean sections in term twin pregnancies rose from 22.5% in 1988 to 60% in 2000 (more than half of these being elective). At the Chelsea and Westminster Hospital during 2006, 114 sets of twins were born at greater than 36 weeks' gestation; 92 (81%) were delivered by caesarean section, and 70 (76%) of these were elective. This is an international trend; as long ago as 1995-2000 in Beirut the caesarean section rate had reached 76.8% in twins born after in vitro fertilisation and 58% in spontaneous twins,15 while a recent paper from Thailand reported an overall rate between 1993 and 2004 of 73.9% (90.6% after in vitro fertilisation and 71.3% for spontaneous pregnancies.16 A randomised controlled trial of elective caesarean section for twin pregnancies is currently under way, coordinated by the University of Toronto maternal infant and reproductive health research unit (which carried out the term breech trial). On the basis of Smith and colleagues' study, the results are likely to show a similar benefit from caesarean section as in the breech trial; however, it is important that we obtain evidence from randomised controlled trials before caesarean section for twin pregnancies at term becomes universal and a trial becomes impossible.