I’ve done some reading about this here IVF process and based on my sources (too many to recount here), I figure any given cycle, the number of embryos in decent enough condition for transfer =

(# Follicles > 15mm @ last ultrasound * R) * S * T * U * V;


R = growth factor after last stim shot = 1.14
S = maturity factor post-retrieval (not all will be mature enough for fertilization) = 0.8125
T = fertilization factor at Day 0 (not all mature eggs will fertilize) = 0.6154
U = decency factor of Day 3 embryos (not all fertilized will be quality at Day 3)= 0.50
V = possibility factor of Day 5 blastocyst (most Day 3s don’t make it to a Day 5) = 0.33

And then the embryo still has to implant.

And continue to grow.

Which really gets me to thinking about the absolute miracle of conception. I mean, it can take months upon months (upon months upon months upon months, et al) to conceive.  The stats above is for an IVF cycle, which can produce anywhere from a few months to a year or more’s worth of viable eggs.  So pare that back and consider you have less eggs to start with going at it naturally, or with Clomid, or even with injectible cycles.  

I guess my point is this: the time it takes to get pregnant is not necessarily an indication of our bodies failing us or that we are somehow failing our bodies, simply that so much has to line up just right.