IVF Success Rates Statistics

1. Embryologist Nikolova, in one of his videos Dr. Stamenov talks about IVF statistics and how to interpret them correctly. What does “success rate” mean when we talk about IVF procedures?

Success rate is the achievement of pregnancy and the birth of a child after an IVF procedure. It is an indicator of the effectiveness of IVF treatment and is usually expressed as a percentage. There is no common methodology for determining success rates so that data can be comparable. It can be calculated in different ways:

• success rate per initiated/financed cycle – percentage of pregnancies per initiated cycle (out of 100 initiated IVF procedures, how many result in pregnancy; this includes procedures that do not reach transfer, frozen eggs, embryos, or those that have stopped developing);
• success rate per embryo transfer – percentage of pregnancies from all performed transfers (if we perform transfer on 100 women, how many become pregnant from that transfer alone, without tracking the remaining embryos);
• cumulative success rate from one and/or several cycles (if we track 100 patients and their fresh and frozen transfers – how many of them reach pregnancy).

2. Patients search for and comment on information about overall success rates and choose a clinic this way. How is correct success rate statistics made?

The term “overall success rate” is not appropriate for comparison between clinics, because all patients are placed under one denominator – regardless of age, and the nature and severity of the problem. To draw correct conclusions, it is important how we group and analyze the data. When comparing success rates between different clinics, similar groups and volumes of patients should be compared. For example, they should be in the same age group. In general, if a clinic has more patients in an older age group, this is a prerequisite for more heterogeneous causes of infertility and more complex cases, which logically leads to a lower overall success rate.

Also, it is not sufficient to collect, for one calendar year, all patients who have undergone oocyte retrieval and report how many of them became pregnant and gave birth, because transfer, achieving pregnancy, and childbirth for some of them do not occur immediately within that same year (there are spontaneous cycles where eggs are collected over months, frozen transfers, etc.).

The question arises whether we should compete for success rates and avoid taking patients who have a lower chance of pregnancy. Where should these patients go, in whom the problem has not been identified, eggs are difficult to obtain, and a large percentage of embryos stop developing? The prospects are not good, they are aware of this, and yet they do not give up and want to try everything. Yes, we will not be able to help everyone, but when we do, it is great – we change human destinies. We want to give our best for every couple, to try to examine the case from all sides, to apply a different type of stimulation, to test the embryos, to perform a biopsy, and to try to achieve pregnancy.

In my opinion, the patient should choose a clinic with good laboratories, established doctors and specialists, where they trust their treating physician, receive the necessary information, and the team works together with them to realize their dream.

3. Patients often hesitate in choosing an IVF clinic and make a decision based on the success rate statistics of the Center for Assisted Reproduction. What should we know about it?

Patients usually inform themselves from the reports of the Center for Assisted Reproduction, but its statistics follow a different approach. In fact, it reports how many procedures were funded during the year for the clinics, and how many pregnancies and births were registered during the calendar year from procedures under the Center, which may have been funded up to 4 years earlier. If there are more funded patients during the year but fewer who reached transfer, the percentage will decrease, which does not reflect the quality of work. I believe that for comparability between clinics, success rates should be compared per transfer or per patient within similar patient groups.

A patient receives an order that is valid for one year from the date of issuance, and it often covers a period of 12 months across two calendar years (for example, from June 2024 to June 2025). Also, one order from the Center may be for 1 retrieval with stimulation or 4 retrievals in a spontaneous cycle. With stimulation, one patient may receive 2, 3, or the maximum of 4 orders within 12 months. In a spontaneous cycle, the patient often undergoes 4 retrievals within 12 months. Very few clinics work with patients on a spontaneous cycle. The total number of funded procedures also includes oncology patients for egg freezing, with whom Nadezhda Hospital works actively.

4. Does the number of patients undergoing IVF in one calendar year matter for success rates?

Definitely yes. Small clinics with a small number of cycles per year can easily report 50–100% success rates, which is not statistically representative. If a clinic has 2 patients in one year and both become pregnant and give birth, that clinic has a 100% success rate. If only one gives birth – it is still 50%, which is a very high percentage.

With 300–1000 patients, the situation changes fundamentally – patients are much more heterogeneous, with different ages, diagnoses, and case complexity. Then the success rate reflects the real clinical work and approaches the average.

5. Which factors influence success rates?

The success rate depends on many factors and is different for each group of patients. I can divide them into two main groups – factors related to the patients and factors related to the clinic.

For patients, in general, success is influenced by the age of each partner, the causes of infertility, the quality of the genetic material, the condition of the uterus and endometrium, and genetic and immunological causes.

For IVF clinics, the influencing factors are the experience of reproductive specialists and embryologists, as well as the quality of the laboratories – embryological, andrological, genetic, and immunological, and in some cases also microbiological, clinical, virological, and pathohistological.

6. Please explain them one by one.

Age is the most critical factor for women. Global data show the best success rates in patients up to 35 years of age. Then the ovaries function best, the probability of obtaining high-quality eggs is highest, and achieving good embryo development is more likely. When we have enough eggs, we can achieve pregnancy with just one stimulation. We can achieve a second and even a third pregnancy from that one stimulation. In men, age also has a negative impact, although sperm parameters do not deteriorate drastically, and this is proven by more and more studies.

Cause of infertility – when we have a specific problem diagnosed in time, it is manageable in most cases. For example, in blocked tubes, the egg and sperm cannot meet, or the embryo cannot reach the uterus. IVF overcomes this problem by transferring a developed embryo directly into the uterus. In male factor infertility with impaired semen parameters, sperm are few in number, poorly motile, and spontaneous pregnancy is difficult. We apply ICSI fertilization and transfer a developed embryo directly into the uterus to achieve pregnancy. But in unexplained factor – when everything appears normal but pregnancy does not occur – finding the problem and the path to success is longer. I dare say that unfortunately, the proportion of patients at Nadezhda Hospital with a combination of several factors, a series of implantation failures, and recurrent miscarriages is increasing, where each pregnancy and reaching childbirth is a serious success.

Quality of eggs, sperm, and embryos – diminished ovarian reserve, poor hormones, embryos that stop developing, lack of normal sperm. Unfortunately, science has not given us tools to improve the quality of reproductive cells, only to observe and assess them. The most difficult cases are when, despite young age, we have poor gamete quality. In women, various stimulation protocols and medications are applied in an effort to obtain quality eggs. In men, we apply special methods for selecting high-quality sperm. In certain cases, nutritional supplements are also prescribed to improve sperm quality, but since spermatogenesis lasts 3 months, they must be taken for at least that period to observe improvement.

Uterus and endometrium – there are different types of uterine abnormalities that hinder pregnancy – thin or excessively thick endometrium, presence of endometriosis, adenomyosis, polyps, fibroids. Therefore, before starting an IVF procedure, precise and accurate diagnostics must be performed.

Genetic causes – about half of embryos have an abnormal chromosomal set. In younger women, the percentage is lower, but with age it reaches 95%. There are also genetic predispositions for forming abnormal gametes, such as chromosomal translocations or monogenic mutations, which are still being studied.

Immunological causes – every embryo is a foreign body for the mother’s organism, and implantation occurs through very complex, regulated, and coordinated mechanisms of the immune system in the uterus.

Laboratory quality – yes, it definitely affects success rates. Strict control of critical parameters is required. The number and type of incubators are of great importance, as well as regular servicing and calibration of all equipment. If culture conditions are not optimal, embryos will not develop normally, which will inevitably negatively affect success rates.

Experience of reproductive specialists and embryologists – experience provides confidence, in-depth expertise, and the ability to view each situation comprehensively and take appropriate actions quickly. Every day is different, every patient is a unique universe, every transfer and every ICSI is different and has its own challenges, and the embryologist must be ready to respond calmly and according to the situation. The number of embryologists is also crucial – there must be a larger number of highly qualified embryologists to ensure interchangeability and smooth laboratory workflow without any compromise in quality.

7. You have long-term experience as Head of the Embryology Laboratory at Nadezhda. What do the data say about success rates at Nadezhda?

As a large hospital, we have a lot of data. The age distribution of the retrievals we performed in 2024 shows that the majority were in women over 41 years of age. Due to the fact that in this age group more IVF procedures are performed in spontaneous cycles and with mild stimulation, we monitor 2–3 follicles. These patients undergo more retrievals until we collect a sufficient number of eggs and manage to reach a high-quality and balanced embryo for transfer. A total of 77% of retrievals are in patients over 36 years of age.

In patients under 35 years of age, stimulation is applied, and with a good ovarian response, we have enough embryos for transfer.