One of the biggest risks of in vitro fertilisation (IVF) has fallen sharply after intervention by the regulator to make the process safer. The proportion of younger women having twin or triplet pregnancies following IVF has declined from almost one in three in 2008 to less than one in four in 2010.

Multiple pregnancies are riskier than singleton pregnancies, with a higher incidence of miscarriage and prematurity – one in five women will lose at least one foetus. The death rate in the first month of life rises from 3 per 1,000 for singletons to 19 per 1,000 for twins and triplets.

But they are common in IVF because of the practice of replacing at least two embryos in the womb – and sometimes, in foreign clinics, many more – in the hope that one will take.

Since January 2009, the Human Fertilisation and Embryology Authority (HFEA) has promoted a policy of replacing a single embryo in the womb, which has reduced the multiple birthrate.