Depending on the “gynaecological circumstances”, in the so-called cryo cycle, an embryo frozen as an egg cell, inseminated egg cell or already frozen as an embryo is transferred into the uterine cavity either in the natural cycle or after hormonal stimulation. This does not require a great deal of effort since the patient only has to come in once for an ultrasound, around cycle day 12, so that the optimal day for the transfer can be identified. If it seems necessary, stimulation therapy with clomiphene tablets is also an option, though there is a possible drawback of a flat mucous lining. Stimulation can also be achieved by means of injection. This does not depend on the egg cells growing under stimulation, but rather on the hormones produced by the follicles.
Another cryo cycle option is what is known as the “artificial” or HRT (hormonal replacement therapy) cycle. In this case, the woman first takes oestrogens alone (either orally, vaginally or transcutaneously), causing the mucous lining in the womb to grow. At the optimal time, progesterone (luteinising hormone administered orally or vaginally) is added. The benefit of this approach is the very low price and the fact that the procedure is not dependent on the status of the ovaries. The disadvantage is that there will be no follicles and thus no corpus luteum to supply the hormones, meaning that the patient will have to continue taking oestrogen and progesterone up to about week 10 of pregnancy.
Depending on the type of cryopreservation and the type of cells frozen, it is possible to achieve pregnancy rates that match those in a “fresh cycle”. There are more recent scientific observations which indicate that the chances of pregnancy in the cryo cycle may even be somewhat better than in a fresh cycle. However, this is not the case for the most common cryopreservation method, slow freezing but only vitrification appears to deliver improved chances.
In our laboratory, we use vitrification except for with sperm. Information on vitrification