Cryopreservation of embryos
If the treatment results in more high quality embryos than those transferred, ‘surplus’ embryos can be cryo-preserved and stored in liquid nitrogen at -196°C. The embryos can later be thawed and transferred usually without the need for any hormone stimulation.
Even though we only freeze embryos of very good quality, not all embryos will survive the freezing and subsequent thawing.
The current legislation in Denmark states that embryos may be stored for up to 5 years. They must be discarded if the couple breaks up or if the woman turns 46 years of age.
If the embryos are the result of treatment of a couple the following applies:
- Both partners must accept in writing that the embryos are cryo-preserved and stored.
- The embryos can only be thawed and transferred if both partners gives written consent before each ’cryo-cycle’
Thawing and transfer of cryo-preserved embryos
The chance of becoming pregnant after transfer of thawed embryos is approximately 30-40%.
In women with a regular menstrual cycle shorter than approximately 35 days, the thawed embryos will be transferred in your own natural cycle.
If your cycle is long (longer than approximately 35 days) we will prepare the endometrium to receive the embryos by having you take estradiol tablets or patches. This is called a ’stimulated’ cryo-cycle.
Transferring thawed embryos in your natural cycle
Transfer of thawed embryos is most often done without any hormone treatment. You should call us when your menstrual bleeding starts and make an appointment for an ultrasound scan on cycle day 10‑12. The scan will evaluate the size of the growing follicle and the thickness of the endometrial lining. When the follicle reaches a diameter of 17‑20 mm you should take an injection og Pregnyl® or Ovitrelle® to induce ovulation. Six days later, we thaw the frozen blastocyst and transfer it to the uterus on the same day.
On the day when we thaw the embryo, you should call the laboratory. The lab will inform you about the quality of the thawed embryo.
The embryo transfer takes place on the day of thawing for cryopreserved blastocysts. The embryo transfer procedure is the same as for ’fresh’ embryos.
On the day of the embryo transfer, you should take a dose of 2500 IU Pregnyl® or Ovitrelle® and this should be repeated 4 days later. These injections will make the ovary produce more progesterone, which in turn will stimulate the endometrium.
Transfer of thawed embryos in an estradiol-’stimulated’ cycle
On day 2-3 of your menstrual bleeding, you start taking estradiol tablets.
After 10-12 days, we will perform an ultrasound scan. When the endometrium has reached an appropriate thickness (over 7 mm) you start taking progesteron (Cyclogest®, Lutinus® or Crinone®) vaginal pessaries or gel in addition to the estradiol.
Six days later, we thaw a frozen blastocyst and transfer it to the womb on the same day. You must continue taking estradiol tablets and progesterone vaginal pessaries until the day of the pregnancy test. If you become pregnant, you must continue the treatment with estradiol and progesterone until you are approximately 10 weeks pregnant.