Home : Contents : IVF Program or Current Management of Infertility : The Mathematics of Multiple Cycles

# Thoughts on the

Mathematics of Multiple Cycles:

How to leave with a Baby

No fertility therapy will work 100% of the time for 100% of people.

In order to leave with a baby, one has to be prepared to undertake a therapy more than one time.

There are many publications that show that any therapy that doesn't work well in any patient after a certain number of tries is not likely to work at all. Depending on the therapy and the research study, a therapy is effective (the pregnancy rate/cycle is relatively linear) for the first three to six cycles of that therapy. People may continue to get pregnant with that therapy but at a rapidly dropping rate per cycle. At Infertility Solutions, P. C., we review our plan with the patient after every three or four failed cycles and either find a way to improve our approach to that therapy, evaluate the patient at a higher level, or move to a more advanced therapy (see philosophy).

Information on expected pregnancy rates per cycle can be found on another web page. However, calculating the expected pregnancy rate after multiple cycles is slightly more complicated than just multiplying the pregnancy rate per cycle by the number of cycles. This has to do with the fact that the population is changing with each attempt to get pregnant. Some people will always have some problems that are more severe than other people have and are less likely to respond to therapy. For example, if a given therapy has a 40% success rate per cycle, not everyone will be pregnant after three cycles even though 40% x 3 = 120%. If 100 people undertake a therapy with a 40% success rate, 40 people will be pregnant after one try and 60 won't. If those 60 undertake the therapy again and 40% get pregnant, then 24 more people will be pregnant, but 36 will not have gotten pregnant. If these 36 people undertake the therapy again and 40% get pregnant, then 14 (36 x 40% = 14.4) more people will be pregnant, but 22 will not have gotten pregnant. Thus after three cycle 78 (40 + 24 +14) out of the original 100 people will have achieved pregnancy. Thus a therapy that has a 40% pregnancy rate will be 78% effective after three cycles.

#### Pregnancy rate comparison

The following table shows the expected pregnancy rate after

three cycles for given pregnancy rates for a single cycle.

Pregnancy Rates |
Single Cycle |
Three Cycles |

Therapy A | 10% |
27% |

Therapy B | 15% |
39% |

Therapy C | 20% |
49% |

Therapy D | 25% |
58% |

Therapy E | 30% |
66% |

Therapy F | 35% |
73% |

Therapy G | 40% |
78% |

Therapy H | 45% |
82% |

Therapy I | 50% |
87% |