Couples must ask about numerators and denominators and certainly the maternal age when they evaluate programs and methods and prepare to manage their sentiments, plans and expectations.
Going through infertility and IVF literature we come across a lot of statistical data with attention to success rates. We must take into consideration that IVF, from initiation of ovarian stimulation to a live birth, is a series of steps that is either continued or stopped at some point. In addition, couples going through IVF have very different problems and causes of infertility at different ages. How can we find compass to navigate us through this ocean of parameters? These success rates are necessary to evaluate our work, compare methods and IVF clinics and offer some kind of prediction, so that couples can shape their expectation and planning.
Information is very helpful to offer clarification. Many descriptive studies and large IVF database results show that the causes of infertility are not major factors and may contribute little in success rates variations. Yet, the single major factor is maternal age. So the best way to report IVF rates is to group cases according to woman’s age. Any IVF events and rates must be referred for similar maternal age groups and disregard other details about underlying causes of infertility.
Other data commonly overlooked are statistical rates, which have a numerator (incidence of the event) and a denominator (the specific group that the numerator referred). We must primarily pay detailed attention specifically to the denominator because it defines the value of the rates. Using steps in an IVF procedure I will attempt to show a paradigm of how easily a single number can misguide an IVF event.
Any IVF events and rates must be referred for similar maternal age groups
Lets start schematically with 100 couples, of a certain maternal age, that finally decide and start ovarian stimulation. Most, but not all of them, lets say 95, will reach the stage of egg retrieval. Lets assume that we get mature eggs from 92, and after the fertilization stage, 85 of them having divided embryos and finally undergo an embryo transfer. Later, 50 have positive and rising hCG serum levels, 45 have positive heart beats and in the end 35 couples return back home with a baby. The most frequent question asked among the community with infertility problems is; what is the pregnancy rate?
According to our example pregnancy rate can be any combination with numerator positive hCG or heart beats or live births and denominator number of women: initiated ovarian stimulation or successful egg retrieval or those that underwent embryo transfer. And the rates in our paradigm can span from 35% live births per women that initiated cycle to 59% positive hCG per embryo transfer. Remember, those numbers must be obligatory referred to a certain maternal age group. So numbers from 35 to 59 can describe the same event. All are legal, but give very different impressions and can easily misguide patients and drive to inaccurate decisions and expectations.
I hope that this paradigm will help couples ask about numerators an denominators and certainly the maternal age group when they evaluate programs and methods and prepare to manage their sentiments, plans and expectations.