The risks to mother and baby in IVF fertility treatment may be less if the pregnancy is a result of the transfer of a frozen rather than a fresh embryo.
These are the findings being announced today (Tuesday, September 4) by University of Aberdeen researchers at the opening of the British Science Festival, which is taking place in Aberdeen from the 4th to the 9th of September.
Researchers at the University of Aberdeen conducted a review of 11 international published studies involving more than 37,000 pregnancies following implantation of either a fresh or thawed frozen embryo in IVF (in vitro fertilisation where the egg is fertilised outside the body).
The findings suggested that there was reduced chance of the mother having bleeding in pregnancy, and babies being born pre-term and with low birth weight when pregnancy resulted as a result of frozen thawed embryos as compared to those resulting from fresh embryo transfer. Risk of perinatal mortality was also found to be lower in babies who were born as a result of frozen embryo transfer.
These findings are reassuring for pregnancies following frozen embryo transfer.
Current practice, in which the best embryos are routinely selected for fresh transfer as a first choice, and only spare good quality embryos are frozen for transfer at a later stage, may no longer prove to be the optimal practice. Further research should be conducted to provide more information on these findings, say researchers.
Their review has just been published in the journal Fertility Sterility.
Dr Abha Maheshwari, Senior Lecturer at the University of Aberdeen, and Consultant in Reproductive Medicine with NHS Grampian, said: “We found pregnancies arising from the transfer of frozen thawed embryos seem to have better outcomes both for mums and babies when compared to those after fresh embryo transfer.
“Traditionally it has been thought that fresh is always better and used as a first choice. Initially there were concerns over the safety of freezing techniques, and it was felt that the quality of the embryo could deteriorate and impact on the health of the child. However, data to date has been reassuring.
“Our findings are a reassuring message for any women who may be anxious that freezing affects the quality of their embryos. In fact, the resulting pregnancy and baby may be healthier when a frozen embryo is implanted.”
With the move towards single embryo transfer, led by the Health and Fertilisation and Embryology Authority in UK, the use of freezing has increased worldwide. With use of vitrification (a method of freezing embryos) the survival of the embryos after freezing and thawing has increased remarkably. There are now studies showing that the pregnancy rates per embryo transfer are equal irrespective of whether fresh or frozen embyros were transferred.
Dr Maheshwari continued: “If pregnancy rates are equal and outcome in pregnancies are better, our results questions whether one should consider freezing all embryos and transfer them at a later date rather than transferring fresh embryos. This represents a major paradigm change in assisted reproduction, and one which could satisfy the twin demands of optimising safety and success.
“The existing data do have a number of limitations which need to be addressed in the context of further research before this strategy should be rolled out into routine clinical practice. The initial step must be to provide robust evidence to demonstrate that elective freezing of embryos can increase the chances of having a healthy baby, which would be best performed in the context of a large randomised, controlled trial.
“In the meantime my advice to women undergoing IVF is that there is no reason, yet, to change the way they approach IVF. However, there should be no concerns about freezing embryos and resulting pregnancies, if your clinic is offering the freezing of spare embryos”.
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