Pregnancy starts with the fertilization of an egg with a sperm to form an embryo, which implants itself to the uterine lining. Therefore, it would not be wrong to say that the embryo is the building block of pregnancy, whether natural or assisted. In context of the commonly used artificial reproductive technique IVF, embryo culture implies the formation of zygote and its growth into a embryo.
IVF starts with egg retrieval from the ovaries of the patient and these eggs are fertilized with sperms to form a zygote. The zygote is then allowed to grow by placing it in an artificial medium and under favorable conditions. The growth of zygote into embryo, or embryo culture, takes 2 to 5 days to be completed. The embryo is then placed into the uterus for the pregnancy to continue in the normal manner.
The success of IVF greatly depends upon the conditions made available for embryo culture, because it is actually a healthy embryo which generates a healthy pregnancy. Therefore, IVF patients need to ensure that the procedure of embryo culture should be carried out to perfection and the embryos remain safe while they are in the lab, before being transferred to the uterus.
Understanding Embryo Culture- The Procedure
Embryo culture is one of the most vital and delicate steps involved in IVF as it requires a great degree of skill and expertise to be completed successfully. A process of 2 to 5 days, it is carried out in a series of steps.
Fertilization: The Formation of Zygote
The procedure begins as soon as the follicular fluid is aspirated from the ovaries of the patient. It is carried to the lab, where the embryologist makes its microscopic examination for identifying the eggs present in it. A special medium is used to wash away the toxins as well as impurities around the egg and the surrounding cells. From here, they are taken into carbon dioxide filled incubators, where they are placed in separate dishes. The eggs are then allowed to mature for fertilization, a process taking 2-6 hours in all.
Once the eggs are mature for fertilization, they are made to combine with the male sperms, which too have been washed. This process is carried out in a dish which contains a culture medium, a fluid comprising of salt, proteins and antibiotics. This medium, known as Human Tubal Fluid (HTF) medium, is specially formulated to facilitate the cell division and fulfill the metabolic needs of the growing embryo. Once set for fertilization, the dish makes it way back into the incubator.
Monitoring of the Embryos
Embryo culture is not just about synthesis of the embryos in the lab, but they also have to be monitored carefully to ensure their quality. The embryo requires a controlled environment to grow and flourish into a healthy one and has to be monitored carefully by a qualified embryologist. The next growth milestone is achieved by the embryo after a period of 18 hours. The stage reached is called the pronuclei stage and it is characterized by the formation of two clear bubbles in the embryo. This is the time where the embryologist discards the embryos without the pronunlei.
The embryos are given another 24 hours to develop and from here on, monitoring is done for cell division. This is the time when the embryos would divide into two to four cells (cleavage stage which comes after 2-4 days), a stage considered favorable for the implant by some clinics. On the other hand, some clinics transfer the embryos later, when they reach the blastocyst stage (after 5 days). The decision is based on factors like the health conditions of the patients and the protocol followed by the clinic.
What is the right time duration of embryo culture?
Another factor which is used to determine the success rate of embryo culture and the safety of the embryos in the lab is the time duration of the procedure. Basically, it can vary from patient to patient, depending upon the reproductive history of both the partners. Accordingly, there are three options made available to the patients to choose amongst.
A two day embryo culture is recommended for the couples which have low number of embryos for implantation or they are not showing reasonable development. At this stage of transfer, the cultured embryos are at a two or four cell stage.
In cases where increased monitoring is needed, three day embryo culture is the feasible option. This is the time when the embryo has reached a six to eight cell stage. The chances of viability of the embryo are better at this stage because they have been checked for cleavage and gene activation.
Patients with history of recurrent miscarriages or failed IVF cycles are suggested to opt for blastocyst stage embryo transfer, which is reached after five days of embryo culture. Here, the embryo (blastocyst) has divided into 12 to 16 cells, giving them better chances to implant and become a successful pregnancy.
Are the embryos being cultured getting the right environment in the lab?
The growth of embryos in the lab is determined by the environment being made available to them. Primarily, two parameters are to be considered in this regard.
- Culture medium refers to the medium in which the embryos are placed during the stage. This medium is specially designed stage-wise, the first one during the stage of initial embryo development/cleavage medium (up to day 3) and the second one in the later development stage/blastocyst medium (from day 3 to day 5). Embryos cultured with normal fertilization are placed in the former while those allowed to reach blastocyst stage or to be taken further for cryopreservation would have to be subjected to the latter.
- Temperature also has to be carefully maintained and monitored to ensure the success of embryo culture process. The temperature inside the incubator has to correspond with that available to the embryo inside the Fallopian tube, which is nearly 37 degree Celsius.
The patient can ensure the safety of their embryos in the IVF lab by checking out whether these factors are being looked after well enough. The success rate of embryo culture can be maximized this way, but the fact is that one should be realistic in their expectations as problems may still crop up despite best care and precautions.
Gaudium IVF is a leading IVF centre, providing world class facilities and lab conditions for its patients. To get these facilities along with the expert advice from the renowned fertility specialist Dr Manika Khanna, get in touch today.