You can look at one IVF success rate and see a low percentage per egg collected, then look at another and see a much higher percentage per embryo transfer. It can feel as though one of them must be wrong.
Usually, neither is.
Each percentage starts counting at a different point. A live birth rate per egg retrieved begins with every egg collected. A live birth rate per egg collection looks at the whole collection procedure. A live birth rate per embryo transfer begins later, once an embryo has already reached transfer.
That difference matters because an egg still has to fertilise, develop and become suitable for transfer before pregnancy can begin. A percentage measured from embryo transfer leaves those earlier stages outside the calculation.
Once you can see where each percentage begins, the figures stop contradicting each other. They start answering different questions.
The three IVF success rates are measuring different things
A live birth rate per egg retrieved starts with each individual egg collected. It follows that egg through fertilisation, embryo development, transfer, implantation and pregnancy.
A live birth rate per egg collection starts with the retrieval procedure as a whole. It looks at whether that collection eventually led to a live birth, sometimes including more than one embryo transfer from the same group of eggs.
A live birth rate per embryo transfer starts much later. It includes only embryos that developed far enough to be transferred.
This is why the percentage per embryo transfer is usually higher. It begins after several earlier stages have already been completed. The percentage per egg retrieved begins before any of them have happened.
What live birth rate per egg retrieved means
A live birth rate per egg retrieved starts with every egg collected during retrieval.
It then follows each egg through every stage that comes after: fertilisation, embryo development, transfer, implantation and pregnancy.
That is why this percentage is much lower than the live birth rate per embryo transfer. It includes eggs that do not fertilise, embryos that stop developing and embryos that never reach transfer.
The figure also changes with age. A percentage that may be reasonable for one age group can be far too high for another.
So an average of around 8% per egg retrieved may be useful in a worked example, but it should not be read as your personal chance from each egg.
What live birth rate per egg collection means
A live birth rate per egg collection starts with the retrieval procedure, rather than with each individual egg.
It asks whether that collection led to a live birth.
The important detail is whether the figure includes only the first embryo transfer or all fresh and frozen transfers created from that collection.
When all transfers are included, the result is a cumulative live birth rate per egg collection. This gives a fuller picture of what one retrieval produced overall.
So before comparing clinic figures, check whether the percentage is based on the first transfer only or on every transfer from the same collection. They are not measuring the same thing.
What live birth rate per embryo transfer means
A live birth rate per embryo transfer starts with the embryo placed in the uterus.
It does not include the eggs that did not fertilise or the embryos that did not develop far enough to be transferred.
That is why this percentage is higher than the live birth rate per egg retrieved. It begins later, after several earlier stages have already been completed.
It can be useful when you want to know what happened once an embryo reached transfer. It cannot tell you what one egg collection produced overall.
One egg collection can produce three different success rates
Take one simplified example:
- 8% live birth rate per egg retrieved
- 40% cumulative live birth rate per egg collection
- 30% live birth rate per embryo transfer
These percentages are describing the same IVF pathway from different starting points.
The 8% begins with every egg retrieved.
The 30% begins only when an embryo reaches transfer.
The 40% looks at the egg collection as a whole and includes the chance of a live birth across all the embryos transferred from it.
That percentage can be higher than the rate per embryo transfer because one egg collection may produce more than one opportunity for transfer.
The figures have not changed because the treatment became more or less successful. The percentage changes because the starting point changes.
Which live birth rate answers your question?
If you want to know what happened from each egg collected, look at the live birth rate per egg retrieved.
If you want to know what one retrieval produced overall, look for the cumulative live birth rate per egg collection. Check that it includes all fresh and frozen transfers from that collection.
If you want to know what happened once an embryo reached transfer, look at the live birth rate per embryo transfer.
None of these is the single “best” success rate. Each answers a different question. The useful figure is the one that starts counting from the stage you are trying to understand.
Why none of these percentages predicts your result exactly
Any success rate is an average drawn from a group of treatment cycles. Your result will also be shaped by details that may be hidden inside that percentage.
These include age when the eggs were collected, sperm factors, fertilisation, embryo development, whether donor eggs or sperm were used, whether embryos were tested, the quality of the laboratory, the transfer itself and the conditions needed for implantation.
The way the result is reported also matters. A pregnancy rate is not the same as a live birth rate, and one transfer is not the same as every transfer from the same egg collection.
The percentage tells you what happened across a group. It cannot tell you exactly what will happen in your cycle.
2 out of 3 embryo transfers do not result in a live birth
Clearly, your goal is to be one of the lucky one in three who succeeds.
The two week wait is not a phase to wait and see. It is biologically active.
Implantation has 5 distinct phases and each has to complete successfully for pregnancy to continue.
During the days between embryo transfer and the beta hCG result, biological activity increases rapidly. The embryo continues dividing while its cells begin taking on different roles in the developing embryo and the structures that will support the pregnancy.
Each new cell must produce energy, copy DNA, build proteins and cell membranes and respond to signals from surrounding cells. As cell division and differentiation accelerate, the demand for energy and nutrients rises with them.
Amino acids are used to build proteins and new tissue. Fatty acids contribute to cell membranes and cellular signalling. Vitamins and minerals are involved in DNA synthesis, methylation, antioxidant defence, immune adaptation and early vascular development.
Metabolic stability influences how energy is supplied and used during this period. The nutritional demand created by this level of cellular activity extends beyond a supplement routine.
The days between transfer and beta are a period of increased nutritional demand while implantation and early development are underway.
Your clinic is not leaving anything to chance, and you shouldn’t either. The role of specific nutrients is critical to your success, and you have an opportunity to support this intentionally.
The Now Baby FET Implantation Meal Plan was built around every one of them.
