For children, the highest risk from being one of a number of multiples is prematurity, with all its attendant problems.
The greatest risk associated with multiple pregnancies is premature birth:
- The average gestation for twins is 37 weeks, compared to 40 weeks for singletons.
- 10% of twin births take place before 32 weeks of gestation compared to just 1.6% of singleton births. The risk of delivery before 28 weeks of gestation is 6 times higher for twins than for singletons.
- Guidelines from NICE show that the risk of preterm birth is considerably higher in multiple pregnancies than in singleton pregnancies, occurring in 50% of twin pregnancies.
- Studies have shown that almost 50% of twins have low or very low birth weight compared with 8% of singletons.
- Research has estimated that on average IVF twins are born three weeks earlier, and weigh between 800g and 1000g less, than IVF singletons.
- Twins are six times more likely to die in the first year of life than singletons (24.1:1000 compared with 4.4:1000).
- In 2013 the rate of neonatal mortality for twins was almost five times higher than for singletons.
- Between 40 to 60% of IVF twins are transferred to neonatal care units when they are born, compared with 20% of IVF singletons. In addition, research has shown that 12% of IVF twins require neonatal intensive care for more than four weeks compared with only 1.6% of IVF singletons.
- Of babies born before 26 weeks, 75% die very soon after birth and before admission to neonatal care. Those who are admitted have a 39% chance of survival, and 62% of those that survive have significant brain damage, retinopathy of prematurity, and/or ongoing oxygen dependence at their predicted due date.
Additional health complications
Numerous other health complications have been linked to multiple births, including:
Respiratory distress: 8% of twins require assisted ventilation and 6% suffer from respiratory distress syndrome compared to 1.5% and 0.8% for singletons respectively.
Cerebral palsy: Twins are between four and six times more likely to suffer from cerebral palsy than singletons. 12.6:1000 twins have cerebral palsy, compared with 2.3:1000 singletons. A European multi-centre study reported that the risk of cerebral palsy is increased by low gestational age and birth weight.
Delay in language development: 6.4% of IVF twins need speech therapy compared with 3.2% of IVF singletons.
Disability: Because twins are far more likely to be born preterm and of low birth weight, they are at much greater risk of disability. One study found that in 7.4% of twin pregnancies, at least one child has a disability.
Congenital malformations: One study found congenital malformations in 6.3% of twins compared with 4.7% of singletons.