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Embryo freezing

Details the outcome of frozen-thawed embryo transfer, and the ethical and moral considerations surrounding it.


Results of frozen-thawed embryo transfer

In most IVF clinics, the transfer of frozen embryo result in a lower pregnancy and live birth rates than fresh embryo transfer. The risk of multiple pregnancy is also lower. In some IVF clinics, the pregnancy and live birth rates after transfer of frozen embryos compared favorably with that achieved after fresh embryo transfer. The live birth rate per embryo transfer cycle varied between 29.2% and 3.8% (HFEA 2000 Patient's Guide).

The success rates depend on many factors; including the woman’s age ,the number of embryos transferred and the method used for freezing embryos. In conventional freezing method, approximately one in four embryos does not survive the freezing and thawing process and those who survive have a lower chance of implanting compared with fresh embryo transfer. In contrast, vitrified embryos not only have a much higher chance of surviving the freezing and thawing process but also have a better chance of implantation. The outcome of pregnancies resulted from frozen embryo transfer is similar to fresh embryo transfer in the incidence of biochemical pregnancy, blighted ovum, early and late miscarriage, ectopic pregnancy, preterm deliveries and term deliveries.

To date, there is no evidence that babies born after frozen embryo transfer have any increased incidence of congenital abnormality.

Ethical and moral issues related to human embryo freezing

There are several ethical and moral issues surrounding  the embryo freezing process. These include the following:

  • Fate of the stored embryos on the death of couple 'orphaned' embryos.
  • Ownership of the embryos if the couple divorce.
  • Safety of embryo freezing.
  • Concern that the length of time embryos have been kept in storage might have a detrimental effect on the outcome of frozen embryo transfer and possible increase in fetal abnormalities. However, no long-term studies have been carried out since the age of the oldest child born as a result of frozen embryo transfer is only 14 years. In addition, there is no evidence that extended storage is detrimental to the outcome of treatment.

What are the options regarding surplus frozen embryos?

Approximately 50% of patients have frozen embryos stored after their IVF treatment cycle is completed, Furthermore; some frozen embryos remain after some couples have completed their families. There are three options available for couple with surplus embryos, and whatever they choose, additional consent must be completed.

  • Disposal of the embryos: the embryos are removed from the liquid nitrogen storage tank and placed in a biohazard waste disposal container. Once the embryos are removed from the storage tank, they lose viability in seconds.
  • Donating the embryos for ethically approved research.
  • Donating the embryos to infertile couple(s). Most centers have long list of patients wishing to receive donor embryos .

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