IVF clinics will be asked to find ways to reduce twin and triplet births, without harming couples' chances of conceiving.

Fertility watchdog the Human Fertilisation and Embryology Authority (HFEA) says it wants clinics to reduce multiple births and the health dangers they carry, by implanting single embryos wherever possible - a policy which has been successful in Scandinavia.

But campaigners say that, in return, couples must have access to a full three cycles of treatment on the NHS.

The HFEA yesterday set a new target for clinics to reduce the rates of multiple births from one in four to one in 10.

Walter Merricks, interim chairman of the HFEA, told the winter conference of the British Fertility Society: "We do not have to risk a fall in success rates to achieve a reduction in risk to baby health and safety. Nor do we have to have a system that places artificial constraints on the treatment of any individual woman."

Clinics are currently permitted to return two or even three embryos to a woman's womb during IVF treatment.

The biggest risk in multiple pregnancies is prematurity and low birth weight. Twins are also six times more likely to suffer from cerebral palsy than single babies, are four times as likely to die during the pregnancy and seven times as likely to die shortly after birth.

It has been estimated that if all IVF children were single births, 126 fewer babies would die each year.

The risks to the mother are also higher when carrying twins as she is more likely to miscarry, develop high blood pressure and to haemorrhage.

But parents have raised concerns that limiting certain couples to having only one embryo implanted in each cycle of treatment would reduce their chances of conceiving and raise the cost because they would have to undergo repeated treatments.

An estimated 75% to 80% of IVF treatment is currently paid for by individuals and only 20 to 25% by the NHS.

Access to treatment varies between Primary Care Trusts (PCTs), despite the 2004 Nice clinical guideline on infertility, which recommends funding three full cycles of IVF, where a full cycle includes frozen embryo transfers.

The National Infertility Awareness Campaign Scotland renewed its call for equal access to infertility treatment.

Its spokeswoman said: "It is much more likely that patients will accept a move to single embryo transfer if they have access to the three full cycles of IVF recommended by Nice."