It is often thought that replacing the maximum of three embryos gives the greatest chance of achieving a pregnancy. However, data collected by the HFEA suggest that the live birth rate for treatments where two embryos are replaced is almost identical to that when three embryos are replaced (so long as more than two embryos were created in the first place).

Replacing three embryos does, however, increase the chances of multiple births (i.e. twins, triplets, quads). There is little advantage, and there may be a considerable risk, in replacing three embryos in such circumstances. IVF Treatments in 1995/6 led to 32% of all IVF births being multiple - the highest level of multiple births yet recorded in the UK.

Although the prospect of twins or triplets may seem attractive, there are many serious risks involved in multiple births. Research has shown that multiple births can lead to a much higher risk of:

complications during pregnancy,

premature birth and low weight birth,

disability and death of infants at, or within, 28 days of birth (known as neonatal death).

Low birth weight babies are much more likely to suffer from serious life-long health problems such as cerebral palsy. The average birth weights are 2.5 kg for twins and 1.8 kg for triplets compared to the average birth weight of 3.3 kg for single babies.

The risk of stillbirth and neonatal death is also greater in a multiple birth than for single babies. For single births from IVF treatment the rate of stillbirth and neonatal death is 8.8 per thousand birth events. The rate is 46.8 for twin births and 82.6 for triplet births.

In addition to the serious risks to the babies' health, a multiple birth can create enormous strains for the parents, including financial difficulties and emotional and physical exhaustion. In some cases the joys of parenthood are greatly reduced by these problems.

It is essential to consider a clinic's policy for reducing the chances of multiple births. Some clinics have a policy of replacing only two embryos in each IVF cycle or of not using stimulation drugs in DI. These policies are designed to reduce the chance of multiple birth. It is advisable to discuss with the clinic how your individual circumstances might influence the decision on the number of embryos that should be replaced during your treatment.