Understanding success rates for fertility treatments

Much is made of fertility treatment success rates and it can be easy to get drawn in by an attention-grabbing headline figure produced by a leading fertility clinic abroad or at home. With the chances of conceiving naturally only 20 % to 25 % per month, in vitro fertilisation (IVF) success rates of 40 % to 50 % can seem very impressive and highly tempting.

Unfortunately, success rates may not be as important as fertility clinics would have you believe, since there are so many factors that can affect your own chances of getting pregnant. They can give you an indication, but you need to know how they can be manipulated. Gaining a thorough knowledge of success rates and understanding how they are calculated for different fertility treatments is vital if you are to get any meaningful information from them.

What are success rates for fertility treatment?

Put simply, success rates are a record of the number of successful fertility treatments achieved, that is, what proportion of treatment cycles results in an established pregnancy. The most usual way of expressing this is the number of pregnancies achieved compared to the number of cycles of in vitro fertilisation treatments undertaken by the fertility clinic. Success rates are usually expressed as a percentage. However, even this simple definition is fraught with hidden complications when comparing success rates between different fertility clinics abroad.

It is important to find out what the fertility clinics count as a successful cycle. For some it is a successful live birth, while for others it is a viable pregnancy confirmed by a fetal heartbeat. This may not appear to be an important difference, but once you pass 38, your success rate for conception will be around 30 %, but for live birth this can be as low as 22 %. Beyond 40, as many as half of all confirmed pregnancies fail to produce a live birth. If you are in the older age group, understanding success rates for fertility treatments in terms of live births will be much more important for you.

How are success rates for fertility treatment calculated?

Understanding success rates involves understanding how they are calculated and the different influences that come into play. Success rates calculated by different fertility clinics will be altered by a range of factors, including:

  • The range and complexity of fertility treatments offered.

  • The age of women the clinic is prepared to treat: a fertility clinic only offering standard IVF to younger women will have a higher success rate than one willing to treat women well into their 40s.

  • Embryo transfer policies: transferring more embryos does lead to a higher rate of pregnancy, but the higher rate of multiple pregnancies and complications may lead to a lower live birth rate.

  • The number of treatments the fertility clinic performs each month or each year. Larger clinics with a higher throughput of cases tend to have higher success rates.

You should always ask for the success rate for your age group and your treatment, rather than accepting an overall success rate that may be enhanced by selection policies.

Success rates for fertility treatments and sample size

Statistically speaking, very few fertility clinics perform enough treatments to produce meaningful data, and the success rates should reflect this with a range that matches the sample size. However this is rarely the case since most clinics want to present the best possible data. Understanding success rates means understanding the sample size and therefore the likely accuracy of the figure being quoted.

The UK’s Human Fertilisation and Embryology Authority (HFEA) quotes the following example to illustrate this point. If a larger fertility clinic has a success rate of 200 out of 1,000 cycles of IVF, then their success rate is 20 %. However, a smaller clinic that has a success rate of 20/100 could also boast the same success rate. To compensate for this, the figures should be expressed as a range, with the larger sample producing a smaller range. In theory, the first clinic should quote a range of 18 % to 23 %, while the smaller clinic should quote a range of 3 % to 56 %.

How recent is the fertility clinic’s data?

As with many statistics, success rates are inevitably out of date before they are even released, and so they may no longer be relevant to the fertility clinic at all. Understanding success rates’ sample dates will tell you how relevant they still are. Live birth rates will always be at least a year out of date because they have to wait nine months for the event to happen, although confirmed pregnancy success rates may be more up to date.

You need to ask each fertility clinic when the data was collected and whether anything has changed since then. If a key specialist has left, or other changes have taken place, then the success rate calculated before these changes will be largely irrelevant.

What do the statistics mean for the success of your fertility treatment?

The main thing to remember about success rates is that they are statistics about previous patients. They are not about you and hold no guarantees for your treatment. For example, if a fertility clinic has an average success rate of 40 %, then on average, 4 out of every 10 clients will fall pregnant as a result of their treatment each cycle. Over three cycles, this rises to around a 90 % chance of conception. Add more cycles and the figure will get higher and higher, but it will never reach 100 %. Even with a high success rate and multiple cycles, there are still no guarantees, and you could be one of the unlucky 60 % who fail to conceive each and every cycle.

Success rates have a role to play in your choice of fertility clinic but understanding how they are derived should encourage you not to give them too high a priority in your decision-making process.

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