A new study has shown that babies born following IVF using frozen embryos may be born later and weigh more than babies born from fresh embryos.
The research looked at 384 babies born after fresh embryo transfer and 108 born after frozen embryo transfer. It showed that babies born from frozen embryos, on average, weighed 253g more and were born four to five days later than babies born from fresh embryos.
Suzanne Cawood, who led the study at the Centre for Reproductive and Genetic Health in London said: 'This is important because prematurity and low birth weight are both risk factors for poorer health later in life and are linked to higher rates of behavioural and learning difficulties. This means that resulting babies may potentially be healthier if frozen embryos are transferred rather than fresh embryos'.
It is not yet clear why using frozen embryos could lead to 'healthier' babies than using fresh ones. Cawood explained, 'one possibility may be that there is a difference in the uterine environment between fresh cycles, when embryos are transferred soon after the eggs have been collected, compared to frozen cycles when the uterus has not been stimulated in the days before transfer. However, further research is needed to test this hypothesis'.
To create embryos for IVF, a woman is treated with hormones to make her produce more eggs. These are then fertilised outside the body and re-introduced to her uterus within a few days. In contrast, embryos which have been frozen are likely to be introduced into a woman who has not undergone this hormone treatment for some time.
According to the Press Association, in 2008 Danish scientists also found that babies from frozen embryos were heavier and suggested this could be due to only top quality embryos surviving the freezing procedure.
Infertility Network UK chief executive Clare Lewis-Jones said: 'If these results prove positive, then we would welcome this and hope it benefits infertile couples everywhere'.
The study was presented at the annual meeting of the British Fertility Society last week.
