In Vitro fertilization STAGES


1. Complete examination of the reproductive status of the man and the woman

When patients wish to be included in our In Vitro program, they receive a detailed plan for the necessary examinations. All of them can be done on the spot at Vita Hospital, which is very convenient and saves much time and travelling.

2. Controlled Ovarian Hyperstimulation (COH).

Controlled Ovarian Hyperstimulation aims stimulation of ovaries to produce several ova (ovocytes) but not only one as it happens in the normal cycle. More ova allow obtaining more embryos which significantly increases the conception chance.

The stimulation itself is carried out by specific medication and definite schemes of application, called stimulation protocols. The protocol for each woman is individual and is permanently made more precise during stimulation monitoring.

Several follicles (small cysts), containing the ova, grow up during the ovarian stimulation. They are monitored by vaginal ultrasound examinations as well as by several hormonal tests. The aim is to achieve maturity of ovocytes and to pass onto the next stage.

3. Follicular puncture and aspiration of ova

The aim of this manipulation is to puncture follicles and aspirate the fluid contained in them – expecting to find ova in it.

Puncture is carried out via vagina, under ultrasound control.

Procedures last approximately 10-20 minutes, depending on the follicle number and is done under suitable anesthesia, monitored by a team of anesthesiologists.

The obtained aspirates are delivered to the embryological laboratory for the next stage.

Embryological procedures

4. Obtaining and processing seminal fluid

The sample of seminal fluid is delivered by the partner on the day of follicular puncture. It is desirable that he had restrained sexually 3-5 days prior to it. In most cases the seminal fluid is obtained by masturbation, for which a premise with all facilities is provided.

In very rare cases, at complete absence of spermatozoa, testicle or epididymis puncture or microsurgical intervention is undertaken. These manipulations are carried out by urologist under general anesthesia.

The obtained sample is processed by different methods pursuant to its indices, in order to obtain sufficient concentration of qualitative spermatozoa for the further fertilization procedures.

5. Classic In Vitro Fertilization (IVF).

Aspirates obtained by follicular puncture (follicle fluid) are examined under microscope and the fit ova are separated from them. The latter are classified by quality and maturity and then placed in a special medium for cultivation.

Several hours thereafter – time depending on maturity of ovocytes, 50-200 thousand seprmatozoa are added to each one of them in the classic In Vitro. No extra procedures are applied for fertilization.


In many cases, the spermogram indications are not so good to apply the classic In Vitro fertilization – insufficient concentration, reduced to missing mobility, big percentage of spermatozoa with abnormal morphology, etc., as well as the unexplainable absence of fertilization in the preceding classic In Vitro. In such situations is used the method of ICSI – Intra Cytoplasmic Sperm Injection into the ovum.

The sole difference in this case is that by the complex micromanipulation system a spermatozoon i chosen, which is immobilized and injected into the ovum cytoplasm.

This method is giving chance to obtain fertilization at extreme low sperm concentration, at strongly reduced mobility, as well as in the cases of microsurgical taking of spermatozoa, which is without any alternative.

It is important to mention that the difference between ICSI and the classic In Vitro is only in the embryological procedure. Monitoring of stimulation and the manipulations, carried out on the patient, are similar.

7. Cultivation of ova and embryos

The ova and the embryos, obtained after fertilization,  “reside” several days outside the woman organism. This is the principle of In Vitro, from where comes its Latin name – “in glass”. In order to be successful, this residence should be at conditions, maximum close to the one in human organism.

It is achieved by:

- special incubators, maintaining the body temperature (37 degrees), 99% humidity and 5% concentration of СО2,

- cultivation media, which composition is close to the maximum to that of the uterine tubes and uterine environment.

If we accept the puncture day as day 0, from then on:

- day 1  fertilization symptoms are looked for – the ovum has two polar corps and two nuclei (pronuclei);

- day  2 the fertilized ova have already started their fission and embryos are obtained, consisting of 2-4 (4 in average ) cells, named blastomers;

- day 3 the embryos have 8 blastomers in average. Embryotransfer is done most often at this stage and the other embryos are frozen;

- day 4 development of embryos continues – 16 and more blastomers;

- day 5 the embryo reaches the stage of blastocyst. Embryotransfer at this stage is recently more and more often conducted

8. Embryotransfer

This term means placement of embryos into uterine cavity. Most often this procedure is done on day three – at the stage of 8 blastomers in average or on day five – at the stage of blastocyst.

Between 1 and 3 embryos are transferred. The aim is to increase the chance of onset of pregnancy to the maximum and in the meantime to reduce the probability for twins.

The decision of the day of transfer and the number of embryos is individual for each couple and is taken jointly by them, the attending physician and the embryologist.

Embryotransfer is performed by special thin catheter via the cervical canal (opening of uterine neck). This manipulation is painless and no anesthesia is necessary.

9. Cryoconservation (freezing) of spermatozoa, ova and embryos

The first successful pregnancy from frozen embryo was reported in 1983. And respectively the first delivered baby by this method – in the next year.

The first baby in Bulgaria from frozen embryo was born in 2001. And the first twins - in 2005.

Nowadays, by large percentage of in vitro procedures (between 30 and 50%) after transfer of 1 to 3 embryo, a freezing is necessary for other viable embryos. The method gives the patient an additional chance for pregnancy, without the need for costly and burdensome for the organism ovarian stimulation and follicular puncture.

In the world by about 26% success rate in transfer of fresh embryos, it is about 18% in the transfer of frozen embryos and the trend is these rates to get more and more close.

There are two main techniques for embryos freezing:

„slow freezing” older and hard procedure, but with great experience in implementing it The freezing process from room temperature to -196 degrees lasts between 2 and 3 hours.

Vitrification - more modern procedure in which the freezing process is almost instantaneous – it takes only a few seconds. According to global studies this method has already yielded a higher survival of embryos and consequently higher pregnancy rate.

Preparing the patient for transfer of embryos can be:

- a spontaneous cycle without any or with minimal drug therapy

- preparation combined with estrogen and progesterone


In both cases the drug load is much lighter than that of ovarian stimulation. The exact time to perform the transfers are determined by the hormonal status of women and the thickness of the uterine lining (endometrium). The aim is to fall into the so-called "implantation window" - the time when the organism of the woman is better prepared to adopt embryos.



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