IVF (in-vitro fertilisation) is a method that allows fertilisation to occur outside the human body by bringing together in the laboratory the female oocytes and the male spermatozoa. The fertilised oocytes thus obtained (embryos) are then replaced in the female uterus.
An IVF cycle comprises several stages :
Ovarian stimulation
The oocytes develop within the ovary, in the follicles. During the natural menstrual cycle, several follicles start to grow as soon as the period starts. Only one or two of these follicles reach maturity approximately 2 weeks later and will be released during follicle rupture (ovulation). Follicles that do not reach maturity stop growing and degenerate. Thus, very few oocytes reach the ultimate ovulation stage during a woman’s life.
The purpose of ovarian stimulation in IVF is to prevent the degeneration of these follicles by exposing them to an adequate dose of FSH. The injection of FSH produces higher circulating levels, which promote the development of numerous follicles and the maturation of several oocytes. This follicular multiplication, also known as controlled, ovarian hyperstimulation, improves the chances of success with IVF by increasing the number of embryos available (To find out more)
The onset of ovulation
When the follicles have reached the desired size and adequate oestrogen levels have been obtained, the final phase in oocyte maturation is induced by an injection of hCG (Choriomon®, Ovitrelle®, Pregnyl®). Follicular needle biopsy (collection of oocytes) is scheduled approximately 35 hours post-injection.
Follicular needle biopsy
Follicular needle biopsy for the collection of oocytes is carried out at the Clinique Générale-Beaulieu. Following the administration of a mild, general anaesthesia, an ultrasound probe fitted with a guide is introduced into the vagina and the follicles are identified. A fine needle is introduced through the guide into the vaginal wall and then the ovary, and the follicles are needle-biopsied individually. The follicular fluid containing the oocyte is aspirated and collected into a tube. The procedure is brief (15-20 minutes). During the procedure, the tubes containing the follicular fluid are maintained at body temperature in an incubator. They are then transported directly to the laboratory where the biologist determines the number of oocytes harvested. Between 8 and 10 oocytes are collected on average after ovarian stimulation. The patient is then taken to a room where the result of the needle biopsy will be announced within one hour. The patient can then return home after a 3 to 4-hour observation period.
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Follicles highlighted by endovaginal ultrasonography during needle biopsy. |
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Oocyte surrounded by cells as seen after needle biopsy. |
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Oocyte that has got rid of its cells. |
The collection and preparation of semen
On the day of oocyte needle biopsy, the partner collects a sample of semen to be used for fertilisation by masturbation.
The Centre for medically assisted procreation at the Clinique Générale-Beaulieu has appropriate, discrete and comfortable venues where this type of specimen can be collected. Although this is a straightforward procedure, it can understandably cause considerable stress.
If the procedure proves difficult, the semen to be used for fertilisation can be cryopreserved in advance.
In cases where the semen has been surgically removed from the testicle or excretory ducts prior to the treatment cycle, cryopreserved semen will generally be used.Regardless of origin, the semen is analysed and prepared in the same way. The seminal plasma that limits the fertilising capacity of the semen is eliminated and the most mobile spermatozoa, which are, in fact , the most fertile, are selected.
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Spermatozoa in the seminal plasma. |
The oocytes are then inseminated. Fertilisation is either left to chance (IVF) or controlled (ICSI – intracytoplasmic sperm injection) depending on the nature of the infertility.
Fertilisation
The ovules are fertilised in one of two ways : « conventional » (IVF) and intracytoplasmic sperm injection (ICSI).
IVF is used when the infertility is of female origin and the quality of the semen is normal or barely altered. A few hours after follicular needle biopsy, the oocytes are placed in contact with the spermatozoa in a culture medium conducive to their survival. They are kept at 37ºC for a period of 4 to 20 hours. Only one spermatozoon – the most active – will cross the Zona pellucida and the plasmic membrane of the ovule and fertilise the egg.
After 18-20 hours’ incubation, the biologist checks via the microscope whether fertilisation has actually taken place. The fertilised (or “impregnated”) oocyte appears in the form of a cell with two nuclei(pronuclei) – one originating from the father and one from the mother. This is known as the zygote stage.
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Zygote presenting 2 pronuclei in its cytoplasm (arrows) |
The zygote is still not an embryo because the paternal and maternal gene pools have not yet merged.At this stage, the biologist retains 2 or 3 zygotes for transfert. Surplus zygotes are frozen (cryopreserved) for transfer during another attempt.Fertilisation anomalies are sometimes observed, making it impossible to transfer or freeze these zygotes.
Embryo development and transfer
Two to three days after collecting the oocytes, the embryos are transferred into the uterus. On the 2nd day, the embryos divide into 2 to 4 cells, reaching the 6 to 8-cell stage on the 3rd day.
The transfer is a painless process. The embryos are placed in a fine, supple catheter. After having exposed the Cervix uteri using a speculum, the doctor gently introduces the catheter as far as the uterine cavity. In some cases, the transfer takes places under ultrasound scanning in order to guide the insertion of the catheter within the uterus and to ensure that the embryos are deposited in the right location.
Two or three embryos are generally transferred. The number of embryos to be transferred is decided after discussions with the doctor, depending on the woman’s age and the couple’s choice. According to Swiss law, no more than 3 embryos may be transferred at any one time.
Approximately 12 days after transfer, a pregnancy test carried out on a blood sample will confirm the treatment outcome. It the test proves positive, an ultrasound scan will be scheduled for approximately 4 weeks after transfer to confirm that pregnancy is proceeding well.
The cryopreservation of surplus zygotes
It is quite common to obtain more zygotes than are required for transfer. Surplus zygotes can be stored in liquid nitrogen, at a very low temperature (freezing or cryopreservation).
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Zygote freezing tray with its identification band |
The aim of zygote cryopreservation is to give couples the best chances of conceiving whilst limiting multiple pregnancies and associated complications. The zygotes can, in fact, be thawed and subsequently transferred if conception fails occurs during the first cycle. In this case, there is no need to repeat the ovarian stimulation and follicular needle biopsy stages.
