What is Fertilization?
Fertilization is the process where a sperm cell meets and fuses with an egg, resulting in the creation of a zygote. This initial cell contains the genetic material of both parents and marks the beginning of a new life. In assisted reproduction, such as in vitro fertilization (IVF), fertilization takes place in the laboratory.
After egg retrieval, the eggs are placed together with sperm in a special culture medium, allowing natural fertilization to occur. In some cases, intracytoplasmic sperm injection (ICSI) is used, where a single sperm is directly injected into the egg to ensure fertilization.
Success Rates
The success of fertilization is influenced by various factors, such as the woman’s age, the quality of the eggs and sperm, and the expertise of the medical team. In general, fertilization success rates in IVF are approximately 70–80%.
This means that the majority of eggs retrieved and attempted to be fertilized will successfully develop into zygotes. However, it is important to note that successful fertilization does not guarantee pregnancy, as the development of embryos and the success of embryo transfer must also be considered.
Can Fertilization Fail? (And What Happens If It Does?)
While the chances of successful fertilization are high, fertilization failure is still a possibility. Common reasons for fertilization failure include:
Poor Egg Quality
Eggs that are not mature enough or have genetic abnormalities may fail to fertilize.
Sperm Issues
Low motility or abnormalities in sperm can hinder successful fertilization.
Challenges with ICSI
In some cases, the ICSI procedure itself may not succeed.
Reevaluation of the Process
The doctor may analyze the reasons for the failure and suggest changes to the method or medications used.
Use of Donors
If egg or sperm quality is the issue, using donor eggs or sperm may be considered.
Repeated Attempts
A new cycle of IVF can be successful, particularly with necessary adjustments and improvements.
Fertilization process
Ovarian Stimulation
Ovarian stimulation is the first stage of IVF, where hormonal medications are used to produce multiple eggs. This is necessary because not all the eggs collected will be healthy or successfully fertilized. Patients are closely monitored with ultrasounds and blood tests to ensure the appropriate development of the eggs.
Egg Retrieval – Fertilization
Egg retrieval is performed through a procedure known as oocyte aspiration, which is done using an ultrasound and a thin needle that is inserted into the ovaries transvaginally. The eggs are collected and then fertilized with the partner’s or donor’s sperm in the laboratory. Fertilization can be done through traditional IVF or with ICSI (intracytoplasmic sperm injection), where the sperm is directly injected into the egg when necessary.
Embryo Transfer
After fertilization, the embryos are cultured in the laboratory for a few days (usually 3-5 days), and then the most suitable embryos are selected for transfer into the woman’s uterus. Embryo transfer is a simple and painless procedure that rarely requires anesthesia. The embryos are placed into the uterus using a thin catheter.
Treatment Protocols
The treatment protocols in IVF can vary based on individual patient needs. Gynecologist M. Tsirigotis will select the appropriate protocol based on factors such as age, AMH levels, the number of follicles on the ultrasound (AFC), health history, and previous response to treatments. The main protocols include:
Short Protocol: Used mainly for women with a normal or high response to hormones.
Long Protocol: Your period starts. Count 21 days, and on the 21st day, you come to our center for an ultrasound to confirm ovulation.
If ovulation is confirmed, on the same day, you start the agonist (Daronda) at a dose of 0.2 ml. It is administered daily at the same time, preferably in the morning with very small deviations (± ½ hour). You will receive more instructions on how to use it and a demonstration from us.
About a week after starting Daronda, your period arrives. On the 4th-5th day, you come for an ultrasound and hormone testing. Don’t forget to confirm your appointment the day before by calling the Center.
If the ultrasound imaging of your ovaries is good and the hormone test (E2, LH, P4) is equally good, from that evening, you start ovarian stimulation treatment with FSH or FSH+LH*. The dose is determined by us, following medical guidance. FSH is administered as an injectable subcutaneously. It is given daily at a fixed time between 6-10 pm. More instructions on how to use it and demonstration of its use will be provided by us.
While continuing the treatment with the above medications, you will come to our center every 2-3 days for a repeat hormone test and ultrasound, according to the instructions given by us over the phone after each visit.
Antiestrogenic Protocols: Used to reduce the production of natural hormones before ovarian stimulation.”
The Psychological Dimension of In Vitro Fertilization
In vitro fertilization is an emotionally charged process that can cause stress, anxiety, and disappointment. It is important for couples to have support from specialized psychologists or support groups to cope with the emotional and psychological challenges that may arise.
Success Rates
The success rates of IVF depend on many factors, but mainly on the woman’s age, the number of eggs and embryos, the cause of infertility, and the clinic’s experience. Success rates are generally higher for younger women and decrease with age. It is important to have an informed discussion based on an assessment of your personal chances of success.
2023 Success Rates
Reproduction after 40
Reproduction after the age of 40 is a common topic of discussion for women who wish to have children at a more mature age. Despite the challenges, advancements in reproductive medicine have significantly improved the chances of success. Surgeon-gynecologist Dr. Marinos Tsirigotis, specializing in reproductive medicine, approaches each case individually, employing the most advanced treatment methods.
Success rates for women over 40 are encouraging, particularly thanks to egg donation and other innovative techniques that are now available. Dr. Tsirigotis and his team design tailored therapeutic plans for every woman, focusing on optimizing pregnancy chances. The personalized protocols, combined with the team’s expertise, result in high success rates.
The support and scientific knowledge provided by Dr. Marinos Tsirigotis are also crucial factors contributing to achieving motherhood, even after the age of 40.
If you’re seeking specialized solutions, don’t hesitate to contact the gynecologist to receive the best possible services!
Under 35 years old
35 – 37 years old
38 – 39 years old
40 – 42 years old
Ask the expert
Ask for a second opinion from Dr Marinos Tsirigotis!

Frequently Asked Questions About Fertilization
Fertilization is usually completed within 12-24 hours of the sperm and egg joining in the laboratory.
In cases of fertilization failure, another attempt can be made with a different approach, such as using different sperm or different assisted reproduction protocols.