Birth rates for IVF twins and triplets have begun to fall in line with government targets aimed at reducing health risks caused by multiple pregnancies.
The drop reflects guidelines brought in by the Human Fertilisation and Embryology Authority (HFEA) that urged UK fertility clinics to limit multiple births to no more than 24% in 2009/10.
Women who carry more than one child have a greater risk of miscarriage and medical complications, including anaemia, haemorrhages and high blood pressure. The babies are also at risk of serious health problems, with twins four times more likely to be born with cerebral palsy than a single baby.
The proportion of multiple births after fertility treatment edged down from 23.6% to 22% between 2008 and the first six months of 2009, according to the latest figures from the HFEA.
Fertility clinics are reducing multiple birth rates by encouraging women to have only one embryo implanted at a time. The rest of their embryos are usually frozen and stored for use later on.
The move towards single embryo transfer raises the upfront costs for couples who have to pay clinics to have stored embryos implanted when they want another baby. Lisa Jardine, chair of the HFEA, said the regulator was "extremely close" to an agreement with the Department of Health that would waive the authority's fee of £104 for this second round of treatment. The cost of standard IVF treatment can be £3,500.
The HFEA says that fertility clinics must bring down multiple birth rates to no more than 15%. The regulator aims ultimately to cut twin and triplet babies to 10% of all IVF births.
"A multiple birth is the single highest risk to the success of pregnancy, the health of the child and the health of the mother," Jardine said. Among naturally-conceived babies, only around one in 70 is a twin. The fall in multiple pregnancies and births follows a rise in women who opted to have one embryo implanted at a time, from 4.8% in 2008 to 14.7% in the first half of 2010. The shift had no apparent effect on overall pregnancy rates, which stood at 31.3% over the same period.
Helen Richens, policy manager at the HFEA, said: "Using single embryo transfer can virtually eliminate the risk of multiple births."
A fall in multiple pregnancies is expected to produce significant savings for the NHS in prenatal care and medical support for mothers and babies. A study in 2006 by the Centre for Reproductive Medicine and Fertility in Sheffield reported that monitoring and care costs rose from £3,313 for a singleton pregnancy to £9,122 for twins and £32,354 for triplets.
A previous study, published by a Dutch group in 2004, found that the cost of a twin pregnancy up to six weeks after delivery was more than five times higher than a singleton pregnancy.
