Contribution of multiple pregnancies to perinatal mortality and morbidity

The twinning rate has increased from 10 per 1000 pregnancies in the 1970s to 13 per 1000 pregnancies. as a result of infertility treatment. But for eveıy twin pair born, at least 10 singletons are conceived as one of a twin pair (the vanishing twin syndrome). The dizygotic to monozygotic ratio is up to 2.0 in some countries. Monozygotic twinning rate is constant worldwide at 3-5 per 1000 pregnancies. Dyzygotic twinning is highest in Africa and lowest in the Far East, with Caucasians and Indians in between (increasing with maternal age and parity). Australian data showed that multiple births account for 10% of perinatal deaths (7% of fetal deaths and 13% of neonatal deaths). Perinatal mortality rate in twins is 4.1 times higher than singletons (stillbirth rate 31 times higher and neonatal mortality rate 5.6 times higher). Data from the United Kingdom showed that the infant mortality rate in twins is 6.2 times higher than singletons. Furthermore, the cerebral palsy rate anıong survivors is 5.5 times higher in twins comparec! lo singletons (difference greatest among term infants). The risk for both mortality and morbidity is increased in monozygotic tvvins tlue to (1) the celi division process leading to chromosomal or other anomalous lethal aberration in one fetus, (2) twin-twin transfusion syndrome (TTTS), and (3) adverse consequences on the surviving fetus after the fetal death of its co-twin. The incidence of TTTS is 15-30% in monochorionic monozygotic twins. Obstetric risks, survival and neurological outcome associated with interventions for treating TTTS (serial amnioredııction, fetoscopic laser ablation of placental vascular anastomoses, amniotic septostomy, and selective feticicle) have been reported, and several randomised controlled trials are in progress.