ембриолог на "Надежда" се подготвя да извърши ICSI/IMSI

reproductive medicine

In Vitro Fertilisation

Classic In Vitro Fertilization (IVF) is a method in which the mature eggs, collected by follicular aspiration, are brought together with the partner’s sperm in the lab, so they are fertilized.

ICSI (Intracytoplasmic Sperm Injection) is a method that is most often applied when dealing with the so-called male factor infertility, or more specifically, with poor sperm parameters. IMSI is a modification of the same method.



For IVF, the eggs retrieved by follicle aspiration are delicately cleaned of excess cells and are placed in a special medium in a lab dish (petri dish) labelled with your names. Spermatozoa that have been previously washed, processed and pre-activated in the Andrology lab are added to the eggs at a specific concentration. After this, the petri dish with the fertilisation medium is placed in the incubator. The aim is that one of the spermatozoa eventually fertilises the oocyte by fusing with it after penetrating the layer of cumulus cells surrounding it and its membrane. The next day, the embryologist will check the eggs for signs that fertilisation has occurred – there should be two pronuclei visible, a male and a female one. The fertilised egg is called the pre-embryo or the zygote. Zygotes are then closely monitored and assessed for regular cellular division in the next two to five days. You will be informed in detail about their development in phone calls by our embryologists.


NB! Various functional defects in the eggs or sperm can interfere with fertilisation. You can ask your fertility consultant about the different fertilisation techniques and the advanced procedures that can be applied to oocytes and sperm as part of the IVF cycle.  

ембриолог на "Надежда" се подготвя да извърши класическо инвитро оплождане
ембриолог на "Надежда" извършва ICSI оплождане на яйцеклетка

ICSI​ (Intracytoplasmic Sperm Injection)

An advanced type of in vitro fertilisation is the ICSI method (short for intracytoplasmic sperm injection). It is similar to classic IVF, but the key difference is that a single sperm is injected into the egg by a special technique. First, before fertilisation, the eggs are prepared by a delicate chemical and mechanical treatment removing the surrounding cumulus cells. Also, their maturity and suitability for fertilisation are evaluated under the microscope before the procedure. The technique is performed using micropipettes under microscopic control through a micro-manipulator. It allows the embryologist to make precise micro-scale movements and become a part of the microcosmos of the gametes.


After the micropipette cuts through the outer egg layer, the zona pellucida and the membrane, the single sperm picked up by the embryologist is injected into the oocyte. After the injection, eggs are placed in a special medium in the incubator. They are checked on the next day for fertilisation results in the form of pronuclei. Fertilised eggs are called the pre-embryos or the zygotes. They will be closely monitored and their cell division evaluated in the following two to five days. Our embryologists will regularly inform you about their development progress on the phone.

ICSI is applied most often when dealing with the so-called male factor infertility. More specifically, when the semen analysis of your partner shows low sperm counts, poor motility, poor morphology, as well as in cases when we have retrieved the sperm by a testicular biopsy.


NB! Both classic IVF and ICSI can be performed using donor sperm or eggs after the partners have completed all the relevant paperwork.

There is no simple answer to this question, and this is why you have to discuss each option with your fertility consultant.


The decision to use one or the other method depends on multiple factors, such as the female partner’s age, whether she has had previous pregnancies, the current cause for infertility, the sperm count, the number of eggs retrieved, their quality, etc.


When there are good semen analysis results and a high number of eggs retrieved, the fertility consultant may choose to apply both methods for in vitro fertilisation combined.

IMSI (Intracytoplasmic Morphologically Selected Sperm Injection)

IMSI is actually a modified ICSI procedure. A single sperm is selected under ultra-high microscopic magnification based on morphological criteria – normal form and size and no visible defects in its head, neck, or tail. The sperm is then injected into the egg’s cytoplasm.

ембриолог на "Надежда" се подготвя да извърши IMSI

Important Information

Preparing for IVF
Egg retrieval
Embryo culture
Embryo transfer and pregnancy test

How to become a patient of the IVF centre

If you still aren’t an IVF patient of ‘Nadezhda’, you first need to submit an online request form for an initial consultation with our fertility consultants. Requests are processed on a first-in-first-out basis. Once a month, they are presented to an expert medical committee that assigns cases to our fertility consultants according to their type and complexity. After your case has been assigned, you will receive a call from the clinic with a proposed date and time for your initial appointment. Please note that due to a large number of requests, the usual time for processing and assignment to our fertility consultants might take up to three months.

See also

Specialised procedures
Specialised tests
Embryology lab
Andrology lab