A new study shows that it is better to use frozen, rather than fresh embryos in IVF treatment. The research was reported by Dr Anja Pinborg at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Barcelona last week. The study has found that babies born from a frozen embryo that was thawed and implanted had a higher birth weight, were less likely to be twins or triplets and had no increased risk of abnormalities, when compared to babies born from fresh embryos.
The study, led by Dr Pinborg of Copenhagen University Hospital Rigshospitalet, Denmark, looked at all 1,278 children born from frozen embryos in Denmark between 1995 and 2006, and compared them to 17,857 children born from fresh embryos. The data shows that on average, babies born from frozen embryos were 200g heavier. In addition multiple birth rates were lower, 14.2 per cent, compared to 27.3 per cent when fresh embryos were used. Dr Pinborg said 'Most encouragingly, we found no increased risk of congenital malformations in the frozen embryos replacement (FER) group; the rate in this group was 7.1 per cent compared to 8.8 per cent where fresh embryos had been used'.
There are several possible reasons why using frozen embryos rather than fresh results resulted in the differences observed. 'Only the very top quality embryos survive the freezing and thawing process' said Dr Pinborg, 'And you only get pregnancies in patients with lots of good embryos to freeze'. In addition, the ovarian stimulation that patients have to go through to collect eggs could negatively influence a subsequent pregnancy, but this does not affect women using frozen embryos.
Freezing embryos allows a couple to have several IVF cycles from the same egg collection, reducing the number of times a woman has to undergo ovarian stimulation. Frozen embryos are implanted into the womb 3-5 days after ovulation, exactly the same way fresh embryos are. As doctors are keen to avoid multiple pregnancies, it is common in IVF for one embryo fertilised in the laboratory to be implanted, and the rest frozen. This new study helps to confirm the safety of using frozen embryos.