3. Success Rates Demystified - tricks to understanding the differences in reporting
It is important that patients understand there are many different ways results are being presented in the media and on clinic websites which calls for caution when interpreting them. To give you an idea of what this means, refer to the graph below which shows the progression of results that are reported based on the different stages of treatment.
The above graph shows, that of
- 100 women who start an IVF/ICSI cycle
- 8 will stop before the egg pick up usually due to poor response, leaving
- 92 to have an egg pick of which
- 23 will have no transfer for one of several reasons including, a freeze only cyle and failed fertilization leaving
- 69 to have an embryo transfer, of which
- 21 will have a clinical pregnancy of which
- 5 will have a miscarriage, leaving
- 16 to have a live birth
1. Live birth is the most meaningful outcome, because not all clinical pregnancies (heartbeat seen at 7 weeks) will result in the birth of a baby due to miscarriages (approx. 23%)
2. Pregnancy rate is interesting but not a recommended outcome as it can be easily misleading for patients who at the end of the day just want a live healthy baby. Clinical pregnancies are reported as a fetal sac or fetal heartbeat seen on ultrasound at 7 weeks of pregnancy.
3. Number of embryos transferred can influence the results, as the more embryos are transferred, the greater the chance of pregnancy and twins. The standard practice in most clinics in Australia and New Zealand is to transfer only one embryo to minimize a multiple pregnancy. This is because multiple pregnancies affect the health and safety of mum and baby.
4. Success rates can be reported for different starting points. Per cycle started includes the 8% of cycles that are cancelled after starting the hormone drugs but before the egg retrieval (OPU) due to complications. Per egg retrieval includes all the women who get to this stage and either have an embryo transfer (with or without freezing) or fail to have one due to either no eggs retrieved, failed fertilization, failed embryo development etc. So results that only report per embryo transfer do not include all the women who have failed to get to this point.
5. Freeze-only cycles are becoming increasingly common to protect both the woman and the embryos if the conditions are not optimal for the embryos to create a pregnancy (e.g. OHSS and abnormal hormone profiles). This means that the number of cycles having fresh embryo transfer in Australasia is declining, because they have been converted to a frozen embryo transfer cycle.
6. Frozen embryo transfer cycles have the same if not higher chance of pregnancy than in fresh transfer cycles. This is mainly because the woman has not taken the ovary stimulating hormones which are known to reduce how receptive the uterus is to implanting embryos.
7. Cumulative Live birth rates refer to the combined chance of getting pregnant from each IVF cycle that results in a fresh transfer plus the subsequent frozen embryo transfer cycles (one or more). Some clinics will present results that state your chance of getting pregnant is for e.g. 70% after two treatment cycles, which will include the frozen embryo transfer cycles that result from those two stimulated IVF treatment cycles.
Essentially, live birth is the most meaningful outcome, because not all clinical pregnancies (heartbeat seen at 7 weeks) will result in the birth of a baby.