Embryos not transferred to the uterus may be
suitable for freezing according to the wishes of
the couple. We recommend freezing when there are
good quality embryos left after the embryo
transfer is completed. Poor quality embryos, or
embryos which are slow to develop, are unlikely
to survive freezing and thawing to give a
reasonable chance of pregnancy.
These embryos can be replaced in a future cycle
without the woman having to undergo the same
drug treatment and surgery. Embryos can be
frozen for up to five years, although this can
be extended to ten years in exceptional
The results following the transfer of
frozen-thawed embryos depend on the number and
quality of embryos available as well as the age
of the woman. Pregnancy rates following frozen
embryo transfer are generally lower than after
transfer of fresh embryos, but it is much
simpler to undertake a frozen embryo cycle.
Frozen embryo transfer has been practised since
1983 and there appears to be no increased
incidence of fetal abnormality in babies born
following this procedure.
Whether to freeze embryos or not is an important
decision for a couple. The couple must give
written consent to storage and their future use.
It is very important that these are completed
accurately as any inconsistencies in the
couples’ consent forms may make the storage of
the embryos invalid. Patients are also
responsible for keeping in touch with the unit
and notifying us of any change of address. The
storage period is governed by law and we do not
need your consent to remove these embryos from
storage at the completion of the statutory
About 70% of all frozen embryos survive the
thawing process. Although some couples may have
all of their embryos survive in good condition,
others may not have any that survive.
Replacement of frozen embryos is relatively
simple. The woman’s natural cycle is monitored
to time ovulation using an ultrasound scan and
ovulation predictor kits. Following ovulation,
the embryos are thawed and transferred back to
the uterus. If the woman’s cycle is irregular we
may recommend hormone replacement therapy (HRT),
which will allow us to prepare the lining of the
uterus for embryo transfer.