Controlled ovarian stimulation during in vitro fertilization treatment involves daily subcutaneous injections containing hormones that stimulate the ovaries. Unlike the natural cycle, where usually one follicle is formed, during such stimulation, several or a dozen of them are created. Obtaining a larger number of follicles increases the number of available eggs, significantly increasing the chances of obtaining healthy embryos and the likelihood of pregnancy. Ovarian stimulation lasts from 10 to 20 days and about 3-5 clinic visits are required, during which ultrasound scans are conducted, and sometimes blood samples are taken to evaluate hormones.

After confirming that most ovarian follicles may contain mature eggs, an egg retrieval procedure is scheduled. The procedure takes place in an operating room, and an anaesthesiologist, gynaecologist, embryologist, and nurse are present. The procedure, lasting about 15 minutes, is performed under intravenous anaesthesia and involves puncturing the ovarian follicles to extract the follicular fluid containing eggs. This is done through the vagina, under the control of a vaginal ultrasound probe. The embryologist evaluates the collected fluid under a special microscope and selects the retrieved eggs (oocytes), which are placed in an incubator.

On the day of egg collection, the male also provides a semen sample for fertilization. Alternatively, the previously frozen sperm collected from your partner/husband or anonymous donor sperm may be used.

The retrieved eggs are fertilized with the partner’s/husband’s sperm (or donor sperm, depending on the situation) on the day they are retrieved. There are two primary types of in vitro fertilization: “conventional” fertilization and ICSI fertilization. “Conventional” fertilization leverages natural mechanisms and occurs when the egg is placed in a laboratory vessel containing sperm. ICSI involves injecting a single sperm cell selected by the embryologist, directly into the egg. ICSI is used when there are too few sperm for conventional in vitro, or when previous in vitro treatment cycles were unsuccessful.

Embryos obtained after fertilizing the eggs are placed in so-called incubators, providing constant, optimal developmental conditions. Observation of embryo development lasts up to 5 days and serves to select the best embryo for transfer to the uterus.

On the day following egg retrieval, we can confirm the number of properly fertilized eggs. This is confirmed by the presence of so-called pronuclei – two structures made of egg cell DNA and sperm DNA. The fertilized egg cell begins to divide.

On the second day of fertilization, the embryo usually consists of 2 to 4 cells (called blastomeres). Every day, the embryologist evaluates each embryo under a microscope and notes down its division progress. Embryo transfer to the uterus can be performed as early as on day 2.

On day 3 of embryonic development embryos usually consist of 6-8 cells. At this stage, much more is known about their pace of development and quality.

On the fourth day, the embryos undergo a major change – the small cells from which they are composed of merge and then smaller cells are separated from them. During this dynamic process, embryo evaluation is challenging, and decisions about embryo transfer are usually postponed to the next day.

On the 5th and 6th day of embryonic development, the embryo should reach the ca called blastocyst stage, consisting of approximately 150 cells. A proper blastocyst forms an embryonic node (from which the embryo develops), a cavity filled with fluid, and trophoblast, which develops into the placenta. Due to the length of observation so far, the blastocyst is the embryo we know the most about. Blastocyst transfer offers the highest chance of pregnancy.

Embryo transfer involves placing an embryo in a droplet of fluid into the uterine cavity. This is achieved by inserting a special, soft catheter through the cervix. The procedure is painless and anaesthesia is not required. Transfer can be performed on the day 2, 3 or 5 following egg retrieval and fertilization. The procedure requires staying in the clinic for about 2 hours.

Properly developing embryos which were not transferred to the uterus, are preserved through cryopreservation. They are placed in “straws” in a special protective solution and frozen in liquid nitrogen. For such embryos, time stops, and they can be stored in this state for years, waiting for thawing and transfer. The latest cryopreservation methods, such as vitrification, are not detrimental to embryos and do not reduce their implantation chances.

* Procedures performed by ANGELIUS Infertility Treatment in Warsaw.