Sperm cells are frozen in a container called a ‘straw’.
The concentration, motility and shape of the sperm cells (morphology) are checked in the lab, after which the sample is frozen. Exactly how many sperm cells are stored in one straw depends on the quality of the sperm sample.
A patient’s sperm sample is often banked as is. This means we do not treat or process the sample first.
To freeze the sperm cells, a specific medium that prevents crystal formation is first added. The sperm cells are frozen in a controlled manner. The temperature drops from +24°C to -80°C for 20 minutes in a controlled rate freezer. The straw is then immersed in liquid nitrogen (-196°C).
When there is no sperm in the ejaculate, sperm can often be obtained surgically during a procedure (see fertility procedures) by removing a piece of tissue from the epididymis, for example. The tissue is examined in our lab and any sperm found is frozen or used immediately.
The straws of one patient are always combined in one protective sleeve. Material from different patients is never stored together. Each straw is labelled with the patient’s name and unique file number. The straw also lists the nature of the tissue (e.g., TESE or ejaculate) and the date of freezing. It is also labelled with a barcode for electronic monitoring through the RI Witness™ system. The sleeve also lists the patient’s details.
Straws containing donor material feature an anonymised donor number and information on how the sample was banked. They are also labelled with a barcode for electronic monitoring through the RI Witness™ system. The sleeve also lists the woman’s unique file number to which these donor straws are linked.
The straws of a known donor list the donor’s unique file number and the barcode for electronic verification through the RI Witness™ system.
When frozen sperm cells are needed for your ART treatment, they are thawed. Two lab technicians collect the necessary straws together from the sperm bank. That way, a double human check is always performed first, followed by the electronic check with RI Witness™, before the sample is effectively thawed and used.
When the straw is thawed, it will be ‘processed’ for use in our Andrology Laboratory. The lab technician washes the sperm and concentrates the sample. The best, most motile sperm cells are selected using light centrifugation through a specific medium (the capacitation gradient). This process is called ‘capacitation’. That way, only the strongest swimmers are retained and we obtain a higher-performing sample for insemination or for further selection for IVF or ICSI.
Typically we need 1 straw for 1 ICSI cycle. Depending on the quality of the sample, several straws may be needed to obtain a reprocessed sample that meets the requirements to perform your treatment.
On average, 50% of sperm cells do not survive the thawing process. The survival rate is related to the sample’s quality. That is why we always prefer a fresh sample in treatments with your own human bodily material.
If someone wants to become a sperm donor, we conduct the legally required health check and also perform a freezing test. We do this to determine how well sperm survive the cryopreservation process. If the survival rate of the sperm sample is not high enough, the donor will not be retained.
If you want to suggest a known donor, this person must meet the same medical conditions and undergo the same tests as anonymous donors. The doctor will advise which pathway is recommended based on the sample’s performance and the freezing test.
Donor straws that were purchased from a foreign bank have usually been processed before being frozen. This means the straw is only thawed and can be used directly for your ART treatment.
The maximum legal storage period for sperm is 10 years. This can be extended for medical reasons. The expense for the cryopreservation of sperm (own material or donor material) is always borne by the prospective parents.
Currently, sperm banking is only reimbursed in case of a cancer diagnosis.
The oocyte is the largest cell in the human body. Unlike a sperm cell, an oocyte contains a lot of fluid (cytoplasm) and is therefore more susceptible to crystal formation when frozen. That is why we use vitrification in our lab for oocyte cryopreservation. This technique minimises the risk of crystal formation. Vitrifying literally means ‘turning into glass’. Using this technique, the material is flash-frozen in liquid nitrogen (-196 °C).
We usually freeze two oocytes per straw.
The straw containing the oocytes always bears the patient’s name, the unique cycle number of the treatment, and the date of freezing. Each straw has its own number and features a barcode for electronic monitoring through the RI Witness™ system.
The straws of one patient are always combined in one protective sleeve (visotube). Material from different patients is never stored together.
Oocytes are more delicate than embryos and usually less numerous than sperm cells for freezing. On average, the survival rate in our lab of thawed vitrified oocytes is about 75%. We have observed significant individual differences, which may also be linked to oocyte quality. When banking oocytes for later use, you may sometimes be advised to have more than one treatment performed for realistic chances of success during subsequent treatments.
When frozen oocytes are thawed for use, two lab technicians collect the necessary straws together from the oocyte bank. A double human check is thus always performed first, followed by the electronic check with RI Witness™, before the straw is effectively used.
Oocyte thawing is done one straw at a time. In practice, when thawing oocytes, we always take your specific situation and available sperm cells into account. After the thawing process, we assess the oocytes in our lab.
The maximum legal storage period for oocytes is 10 years or until the day before your 48th birthday. If you are under 48, the storage period may be extended for medical reasons. The cost for storage is borne entirely by the patient.
Currently, oocyte banking is only reimbursed in case of a cancer diagnosis, for women with borderline ovarian tumours, and people with rare blood diseases.
We can also successfully freeze and store embryos using the vitrification technique. Each embryo is frozen separately in a straw.
The straw always bears the prospective mother’s name, the unique cycle number of the treatment, the embryo number, and the date of freezing. Each straw has its own number and a barcode for electronic monitoring with the RI Witness™ system.
Our database also records the embryo’s quality score. Based on this, the embryologist decides which embryo will be considered for transfer first.
Embryos are frozen by default if IVF or ICSI treatment produces multiple embryos. We usually aim for a fresh transfer following oocyte retrieval. Any good-quality supernumerary embryos are frozen in that case. If your treatment did not result in pregnancy or if you want another child later, the banked embryos are used first before starting a new stimulation cycle.
If your body reacts (too) strongly to stimulation hormones and there is a risk of overstimulation (OHSS), all embryos will be banked. This gives your body time to recover and we can transfer the embryo back into the womb during a next cycle.
Embryos can be frozen at different days of development. Generally speaking, embryos cope well with the freezing procedure. For embryos on day 3 of development, we offer a survival rate of around 95%. Embryos that grow to day 5 of development (blastocyst) have a survival rate of around 98% in our laboratory.
When frozen embryos are thawed for use, two lab technicians collect the straw together from the embryo bank. A double human check is thus always performed first, followed by the electronic check with RI Witness™, before the straw is effectively used. After thawing, the embryo is assessed.
The number of embryos that will be transferred into the womb is determined in consultation with your attending physician. Moreover, this is also legally capped. Given the high success rates with frozen embryos, we usually opt to transfer only one embryo per attempt.
After IVF/ICSI treatment, supernumerary embryos are stored for 5 years. The storage cost is included in the lump sum for reimbursement of Belgian mutual health insurance funds if you meet the criteria for reimbursement. This deadline may be extended for medical reasons, subject to a doctor’s recommendation. The cost for extension of the storage period is always borne by the prospective parent.
Did you know?
What happens after the storage period?
When you start treatment, you and your partner will establish what happens to the sperm cells, oocytes, and/or embryos after this legal storage period expires. You decide independently what happens to gametes. The decision for embryos must be taken together. You lay down in a contract what we have to do when the cryopreservation expires. You can donate your gametes or embryos for scientific research or request that they are destroyed immediately. You can also opt to donate the frozen human bodily material anonymously for the treatment of other prospective parents.
Five frequently asked questions about cryopreservation:
Is cryopreservation of human bodily material and embryos safe?
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