IVF success rates – what do the numbers really mean?

If you are considering IVF, it’s only natural that you want to understand your chance of success. The good news is that as the scientific processes and technology used in IVF have improved, so too have IVF success rates.

In 2017, the number of IVF births in Australia and New Zealand was the highest in IVF’s 40-year history – for every 100 treatment cycles started, 18 babies were born.1

However, the likelihood of success is different for everyone and is particularly influenced by the age of the woman. This means that when you are reviewing IVF success rates – at either a clinic or population level – you should look at data specific to your age group. For example, for women aged younger than 30 years, the live birth rate per fresh embryo transfer (using the woman’s own embryos) was 38.5% in 2017 but this figure dropped to 23.7% for women aged 35–39 and 8.9% for women aged 40–44.In 2017, the average age of women undergoing IVF and using their own eggs was 35.7 years while the average age of women undergoing IVF using donor eggs or embryos was 40.3 years.1

IVF success rates are not represented as a single percentage probability. Instead, there are several different figures that clinics may use to report their success rates and the different terms can be confusing. For example, you might wonder what the difference is between a ‘clinical pregnancy rate’ and a ‘cumulative pregnancy rate’, or why there are generally more births per ‘egg collection’ than there are per ‘embryo transfer’.

This article provides an overview of the different figures you might see and what they mean. Before reading the rest of this article, you may find it helpful to refamiliarise yourself with the different steps that make up an IVF treatment cycle.

Live births/pregnancies per treatment cycles commenced

An IVF treatment cycle starts with hormonal stimulation – when you start taking medicine after your period to encourage your ovaries to produce lots of eggs. The IVF treatment cycle ends when a fertilised egg (now called an embryo) is transferred back into your womb in the hope that it will successfully implant in the wall of the uterus, thereby establishing a pregnancy.

The number of live births/pregnancies per treatment cycles commenced describes the number of pregnancies and live births achieved for women that started an IVF cycle (with the intention of a pregnancy, not just to freeze eggs), regardless of whether or not they progressed to subsequent steps of the cycle. So this figure includes cycles that were started, but were subsequently cancelled, or where there were no eggs to collect or no suitable embryo to transfer.

In 2017, 22.9% of initiated cycles resulted in a clinical pregnancy* and 18.1% in a live birth.The disparity between the two figures is due to miscarriage or stillbirth.

*A clinical pregnancy is where baby’s heart was heard on ultrasound, usually at around 7 weeks, i.e. not just a positive blood (hCG) test.

Live births/pregnancies per egg retrieval

Measuring the number of live births or pregnancies per egg collection, indicates how successful IVF is in woman who proceeded as far as egg collection.

In 2017, the overall clinical pregnancy rate was 43% per egg retrieval cycle, with a live birth rate of 34%. These figures include cycles where no eggs could be collected (e.g. due to a lack of eggs), as well as cycles where eggs were retrieved but they did not result in embryos for transfer.

*You may also see egg collection referred to as egg retrieval, oocyte pick-up or OPU.

Live births/pregnancies per embryo transfer

Embryo transfer is a critical step in the IVF process, where the developing embryo (fertilised egg) is transferred back into the woman’s womb (uterus). Unfortunately, success rates per embryo transfer can be misleading, because the success of this step is highly dependent on the quality of the embryo, and whether the embryo is transferred fresh or frozen first, then thawed.

These days, embryos may also be genetically screened before transfer, in order to select the highest-quality embryo available for transfer, thereby increasing the likelihood of a successful pregnancy. This type of screening is not recommended for everyone; moreso for older women and/or women who have experienced recurrent miscarriage or multiple, failed IVF cycles. Where genetic screening has been employed, the pregnancy rate per embryo transfer is likely to be higher – and is one of the key reasons why IVF success rates have improved over recent years. However, this means that this figure may not be a good reflection of your own chances of success.

In 2017, the overall rate of pregnancy for cycles reaching embryo transfer was 33.9%, with a live birth rate of 26.8%.1

Implantation rate

The implantation rate describes the number of pregnancy sacs seen given the number of embryos transferred in an IVF treatment cycle. An embryo transfer is considered successful when the embryo implants, i.e. physically attaches itself to the wall of the womb. However, the implantation rate does not tell us how likely these embryos are to go on and result in a clinical pregnancy or live birth.

Live births/pregnancies per implantation

The live births or pregnancies per implantation indicates the percentage of women that went on to achieve a clinical pregnancy or live birth after an embryo had successfully implanted following its transfer into the womb.

The cumulative live birth or clinical pregnancy rate

The cumulative rate for live births or clinical pregnancies is likely to be higher than all the other figures we have described so far. This is because it measures results over multiple IVF attempts, meaning that compared to a single cycle, there are more opportunities for success. The cumulative rate can be measured against either a predefined number of IVF cycles, or it can be measured against the total number of cycles that were attempted by each person.

Which measure of IVF success is most important?

The IVF success rate that is most relevant to you will depend on your individual circumstances, including your age and whether you have had IVF before – and if you are in a cycle right now, what stage of the IVF cycle you have progressed to.

If you are just starting to think about IVF and have not begun treatment yet, then the cumulative live birth rate can help you understand the average success rates for people after their IVF journey is complete.

If you have had one unsuccessful cycle of IVF so far, the cumulative live birth rate can give you an idea of your chance of success if you go on and have additional cycles.

However, the cumulative rate (and other success rates mentioned here) do need to be interpreted with a high degree of caution, because numerous factors influence a couple’s chance of success with IVF.

What else do you need to take into account when interpreting success rates?

Not all IVF cycles are the same. When interpreting data, you should check whether advanced scientific techniques such as ICSI, IMSI or pre-implantation genetic screening were used, and whether the data pertains to fresh versus frozen embryo transfers. This will enable you to review success rates for IVF treatment cycles that most closely resemble your own.

If you are looking at overseas data, keep in mind that single embryo transfer is considered best practice in Australia (in an effort to avoid the risks associated with multiple pregnancies). However, international clinics may offer multiple embryo transfers (transferring more than one embryo into the womb at a time), in which case their IVF success rates per embryo transfer may appear higher.

To gain an understanding of how successful IVF is in Australia, you may like to review this national data collated by The University of NSW.

Weighing up your chance of success?

To get a realistic understanding of your chance of success, it’s best to consult a fertility specialist, so you can receive advice specific to your personal circumstances. If you are looking for a way forward but are not sure where to start or what to try next, you can book an appointment with Nicole, Martin, Chris, Sameer or Hugo by calling (03) 8080 8933 or by booking online. We welcome women and couples who are just starting to consider their fertility treatment options, as well as those who may be seeking a second opinion after treatment elsewhere.

Further reading

References


  1. Australian & New Zealand Assisted Reproduction Database (ANZARD). Assisted Reproductive Technology in Australia & New Zealand 2017 (report). Available at https://npesu.unsw.edu.au. Last accessed 29 October 2019.