IUI statistics explained

Mike pointed out I had made some (embarassing) mistakes in my post on statistics. I went back and fixed the numbers below. After a 36 minute walk tonight, we arrived at this method to getting the “right” numbers. Apply with caution.

Assume your chance of getting pregnant with one follicle from IUI was p%. (This is the biggest unknown of the whole process, I don’t know what it is for me or anyone else. It is probably something between 0 (if you have completely blocked tubes or no sperm) or 20 which is the normal fertile person’s statistic.) Your chance of not gettign pregnant from one follicle would be (1-p)%. If you have n number of follicles, to calculate your probability of getting pregnant, complete the following (use the decimal numbers, i.e. 10% = .1):

Prob of not getting pregnant = (1-p)^n

Prob of getting pregnant with anything = 1-(1-p)^n

Prob of getting pregnant with a singleton = (p*(1-p)^(n-1))*n

Prob of getting pregnant with twins = (p^2*(1-p)^(n-2))*n!/[(2!)(n-2)!]

Prob of getting pregnant with trips = (p^3*(1-p)^(n-3))*n!/[(3!)(n-3)!]

Prob of getting pregnant with quads = (p^4*(1-p)^(n-4))*n!/[(4!)(n-4)!)

Prob of getting pregnant with "m" babies (for m<=n) = (p^m*(1-p)^(n-m))*n!/[m!(n-m)!]

If p=.05 (5%) and n=6 (my guess for my rate and the number of follicles I currently have):

Prob of not getting pregnant = 73.5%

Prob of getting pregnant with anything = 26.5%

Prob of getting pregnant with a single = 23.2%

Prob of getting pregnant with twins = 3.1%

Prob of getting pregnant with trips = 0.2%

I think these are the statistics my RE gave me when I asked for the probabilities of getting pregnant with twins and trips. He said “If pregnant, you have a 10% probably of twins (~3.1/26.5) and a 1% probability of getting pregnant with trips (~.2/26.5)” so I deduce he thinks I have a 5% chance of getting pregnant with a single follicle.

I promise not to bring this up again (until the next cycle…)