Introduction

This article is intended to provide an overview of the most important information on the success of infertility treatment and factors influencing success.

When considering the probability of success, it should always be kept in mind that each case of an unfulfilled desire to have a child is different. The probabilities listed here reflect an average over many cases of unintended infertility. Depending on the specific causes of the unfulfilled desire to have a child, an individual case can very quickly lead to the fulfillment of the desire to have a child through the right treatment, or in the worst case it may not even be possible for a woman to bring a healthy baby into the world.

Basis: Pregnancy vs. live births

When considering the probability of success, a distinction must always be made between the probability of pregnancy and the probability of live birth, since not every pregnancy results in a live birth.

Since the actual goal of infertility treatment is not pregnancy per se, but live birth, only data on live births are considered below, as far as available.

In principle, it should also be warned in advance to directly compare data from different sources on the probability of success of a live birth. In addition to the difference just mentioned, large variations between different years, methods, countries and clinics can be observed in the probability of success – if only because it is often difficult to compare the group of women forming the respective data basis with another group (especially with regard to the age of the woman, but also with regard to the underlying causes of involuntary childlessness). 

Factors that affect the probability of success

1. age of the woman

Description: With age, fertility declines relatively early in all women, and the decline in fertility is particularly more pronounced after the age of 35. Generally, the older a woman is, the higher the risk that she will have to deal with impaired maturation of her eggs or that her egg reserve will be limited.

Data: According to data from the German IVF Registry over the years 2016-2020, the probability of success for live births remains relatively constant at 30-33% up to the age of about 34 and starts to decrease increasingly faster over the following years to below 20% at 39 and finally below 3% for women 45 and older.

Source: German IVF Registry Yearbook 2021

Special case of egg donation:  Eggdonation is a special case, because the egg usually comes from young and healthy women. In a 2017 study by the European IVF Monitoring Consortium, a probability of success for live births in egg donation was found to be approximately 31% across all European countries – regardless of the age of the gestating mother. In contrast, the probability of a successful live birth for women who underwent IVF treatment in Switzerland in 2017 was approximately 28% for women younger than 34, approximately 17% for women in the 35-39 age group, and approximately 8% for women 40 and older. 

Source: ART in Europe, 2017: results generated from European registries by ESHRE

2. method of artificial insemination

Description: The exact method of artificial insemination also has an impact on the likelihood of success, as some methods are better suited to address specific fertility limitations.  

IVF vs. ICSI: When comparing the IVF and ICSI methods, it is noticeable that the ICSI method results in a slightly lower level of live births in most age groups, for example. of 30-34 in IVF about 31% and in CSI about 30%. 

However, it should be noted here that the choice of the method of artificial insemination should always be made together with the doctor and should be based on the individual situation of the woman. The only slightly weaker performance of the ICSI method can even be interpreted as a positive result, since ICSI is a method for more severe cases of infertility – or in other words, the couples undergoing ICSI treatment are usually more difficult cases than the couples undergoing IVF treatment. 

Source: German IVF Register Yearbook 2021

Fresh cycle vs. thaw cycle: Sometimes in the context of IVF/ICSI there is no possibility to transfer the embryos directly fresh into the uterus and the transfer has to be postponed to a later time. For this purpose, the embryos are frozen and later transferred in a so-called thawing cycle. 

In a simple comparison of fresh cycle and thaw cycle in IVF and ICSI, it is noticeable that the proportion of live births is significantly higher in the context of a fresh cycle with about 26% than in the context of a thaw cycle with about 21%. 

However, as with all of the comparisons listed here, this pattern should not be a reason to choose a different method of embryo transfer – several things should be considered with regard to comparing the probability of success with IVF and ICSI:

• Fresh cycle and defrost cycle are not the same cases. The cases where a defrosting cycle is applied are often more complex
• There are usually good medical reasons why embryo transfer does not occur directly, for example, transfer of previously frozen embryos may be beneficial for women with polycystic ovary syndrome (PCOS) or women who show signs of hyperstimulation
• Furthermore, there are scientific studies that show experimentally (i.e., without the problem of cases differing between the two methods) that there is no significant difference in the probability of success between fresh cycle and thaw cycle (see Lan et al., 2018; Shi et al., 2018)

Based on these limitations, the decision between fresh cycle and thaw cycle should always be made together with the treating physician, taking into account, of course, the additional costs and the possible additional burden of a thaw cycle.

Source: German IVF Registry Yearbook 2021

3. number of embryos transferred

Description: By transferring two embryos instead of one, the probability of success of an IVF or ICSI cycle can be increased, as there is a higher chance that one of two embryos will successfully complete the transfer and pregnancy than just one embryo.

Data situation:

In Germany, the probability of a live birth in an IVF/ICSI fresh cycle is about 26% for the transfer of one embryo and about 30% for the transfer of two embryos. 

However, this higher probability of success comes with two interrelated side effects:

• The probability of multiple birth is very much increased in case of transfer of two embryos from about 2% in case of transfer of one embryo to about 28% in case of transfer of two embryos
• Carrying multiples may also result in more frequent preterm births and lower birth weights with associated health risks

Furthermore, as with all comparisons listed here, the cases where one embryo vs two embryos are transferred are not necessarily the same. For example, the transfer of two embryos occurs more frequently in older women than in younger women.

Source: German IVF Register Yearbook 2021

4. number of attempts 

Description: With repeated attempts the probability is higher that sooner or later it will work out with the desire to have children.

Data: According to data from Germany, the cumulative probability of success in terms of pregnancy doubles from about 34% at the first attempt to about 66% by the 4th attempt. In other words, 2 out of 3 women who have perceived up to 4 attempts with IVF or ICSI become pregnant, with only 1 out of 3 becoming pregnant on the first attempt. If all of a woman’s attempts are included, as many as 7 out of 10 women become pregnant.

Note: in this analysis, data on pregnancy success in terms of live births are not available.

Source: German IVF Registry Yearbook 2021

5. country differences

Description: Due to various differences between individual countries (e.g. equipment of fertility clinics, training and experience of the treating health personnel), there may also be differences in the probability of success in terms of live births  in different countries. 

The situation is similar for individual clinics, whose equipment and staff also normally differ.

Data situation: According to a survey by the European Society of Human Reproduction and Embryology (ESHRE), there were significant differences in the likelihood of success of IVF treatment in a number of countries in 2017. In this context, countries with a notoriously well-equipped health care system, such as Switzerland and Germany, showed a relatively high probability of success of about 18%. The same was true for countries that are relatively popular for medical tourism for infertility treatment, such as Spain and Greece (about 18-19% probability of success), although there were also European countries with a relatively low success rate despite a good reputation of the health system, such as Italy with about 15% and Denmark with about 13%.

It should be noted here, of course, that in addition to the equipment and training of the personnel, the cases also vary greatly from country to country (and also from year to year). 

At the end of the day, the quality of the specific fertility clinic and, of course, the price of the fertility treatment should be the deciding factors for the individual patient. The choice of a suitable country may become relevant if certain treatment methods are desired that are not available in all European countries (e.g. egg donation). 

Source: ART in Europe, 2017: results generated from European registries by ESHRE

Conclusion

It turns out that a variety of factors have an impact on the likelihood of success of infertility treatment. 

Overall, there are three important messages that emerge from or despite the above considerations: 

1. The choice of a treatment method and the success of infertility treatment always depends on the individual factors for the unfulfilled desire to have a child – a woman’s age is one of the most important here
2. Patients should always make the choice between transfer of one or two embryos and between fresh cycle and thaw cycle in close consultation with their physician
3. Many European countries have similar success rates in fertility treatment – relevant decision factors here should be, in particular, the quality of the individual hospital, the costs, and, if applicable, the regulatory framework (keyword: egg donation).

Last update: November 10, 2022