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Success rates explained

There are many ways to measure the success rates achieved by a centre for medically assisted procreation and it is normal to feel overwhelmed by all these figures. For example, the success rates for IVF or ICSI are typically presented in one of the following ways:

  1. They can be expressed as the percentage of pregnancies achieved in relation to the number of treatment cycles started during a given period. This data is called the pregnancy rate per cycle.
  2. They can also be expressed as the percentage of pregnancies achieved in relation to the number of follicular puncture cycles performed during a given period. This is called the pregnancy rate per puncture.
  3. They can also be expressed as the percentage of pregnancies achieved in relation to the number of embryo transfer cycles performed during a given period. These data are called the pregnancy rate per transfer. The pregnancy rate per cycle is always lower than the pregnancy rate per transfer since some cycles have to be cancelled after they have been started and do not lead to embryo transfer.
  4. The implantation rate differs from the pregnancy rate. It gives the percentage of embryos which are implanted compared to the number of embryos transferred in a given period. It thus represents the capacity of each embryo transferred during this period to implant in the uterus and to result in pregnancy.
  5. The live birth rate is different from the pregnancy rate because about 15 % of pregnancies achieved by MAP end in miscarriage. It givens the number of live births either per cycles started or per embryo transfer cycle performed.

Here is a simple example to make things clearer.
In one year, 100 cycles were started, 90 cycles resulted in follicular puncture and 80 in embryo transfer, 40 resulted in pregnancy, 6 of which ended in miscarriage. In the same year, a total of 180 embryos was transferred resulting in 26 single-baby pregnancies and 6 twin pregnancies. The 34 babies were born alive.

  1. Pregnancy rate per cycle is 40 % therefore (40 pregnancies for 100 cycles).
  2. Pregnancy rate per puncture is 44% (40 pregnancies for 90 punctures).
  3. Pregnancy rate per transfer is 50 % (40 pregnancies for 80 embryo transfers).
  4. Implantation rate is 21% (38 embryos implanted out of 180 transferred embryos)
  5. Live birth rate per cycle is 34 % (34 live births for 100 cycles).
  6. Live birth rate per transfer is 43 % (34 live births for 80 embryo transfer cycles).

Success rates can also be assessed on the basis of the zygotes or embryos which have been frozen during a previous attempt. In this case, the results can be presented as follows:

  1. They can be expressed as the percentage of pregnancies achieved in relation to the number of frozen embryo transfer (FET) cycles started during a given period. These data are called the pregnancy rate per FET cycle.
  2. They can also be expressed as the percentage of pregnancies achieved in relation to the number of zygote or embryo thawing cycles performed during a given period. These data are called the pregnancy rate per thawing.
  3. They can also be expressed as the percentage of pregnancies achieved in relation to the number of frozen embryo transfer cycles performed during a given period. These data are called the pregnancy rate per transfer. The pregnancy rate per thawing is always lower than the pregnancy rate per transfer since some zygotes or embryos do not survive thawing and thus do not result in a transfer.

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