Risks to the child

For children, the highest risk from being one of a number of multiples is prematurity, with all its attendant problems.

Premature birth

The greatest risk associated with multiple pregnancies is premature birth:

• Research in the UK found that twins were born on average at 35.8 weeks, compared to the 40 week average for singletons. A study in the US found that at least half of all twins were born prematurely (before 37 weeks) and at low birth weight.
• An American study reported that 11.8% of twins compared to 1.6% of singletons are born before 32 weeks of gestation.
• International research concluded that, as a rough estimate, in vitro fertilisation (IVF) twins are born with an average gestational age 3 weeks earlier than IVF singletons and with a mean birth weight ranging between 800g and 1000g less.
• An Australian study found that 48.4% of twins had low and very low birth weight compared with 8.2% of singletons.

Perinatal mortality 

• Twins are 6 times more likely to die in the first year of life than singletons (24.1/1000 compared with 4.4/1000).
• In 2003, had all IVF babies born in the UK been singletons, the deaths of an estimated 126 babies could have been avoided. 

Neonatal care

• Between 40-60% of IVF twins are transferred to neonatal care units when they are born, compared with 20% of IVF singletons.  In a Belgian study, intensive care stays of more than four weeks were endured by 11.7% of IVF twins, but only 1.6% of IVF singletons.
• The risk of delivery before 28 weeks is 1.2% for twins compared to 0.2% for singletons.
• Research in the UK and Ireland found that 75% of babies born before 26 weeks died very soon after birth and before admission to neonatal care. Those admitted had a 39% chance of survival. 62% of those that survived had significant brain damage, retinopathy of prematurity, and/or ongoing oxygen dependence at their predicted due date. 

Respiratory distress

In a Belgian study, 8% of twins required assisted ventilation and 6% suffered from respiratory distress syndrome compared to 1.5% and 0.8% for singletons respectively.

Cerebral palsy

Several studies have shown that twins are between 4 and 6 times more likely to suffer from cerebral palsy than singletons. 12.6/1000 twins had cerebral palsy, compared with 2.3/1000 singletons. A European multi-centre study reported that cerebral palsy risk was increased by low gestational age and birth weight. 

Delay in language acquisition:

Twins have more problems with language development. Research in Denmark found that 6.4% of IVF twins needed speech therapy compared with 3.2% of IVF singletons.

Disability

A Japanese study reported that in 7.4% of twin pregnancies at least one child had a disability.

Congenital malformations

A Swedish study reported congenital malformations in 4.7% of singletons and 6.3% among twins.