[quote=icanhazbabies]Ghost, thanks, this is the best explanation I have read anywhere!
I can sleep easy tonight then!
I have one more question - my RE has asked me to stop Menopur immediately, while continuing Follistim.
Do you think this is because the LH in Menopur could possibly induce ovulation? Can the body be tricked into thinking there is an LH surge?[/quote]
The “LH activity” in menopur is actually a tiny amount of hCG. I think it’s around 20 IU, but I don’t recall for sure. Whatever it is, it’s way too small to mature the oocytes.
hCG and LH activate the same receptors in the ovaries. This has two main effects. One is to mature the oocytes. The other is after ovulation, to keep the follicle (now called a corpus luteum) making hormones, most importantly progesterone and estradiol to prepare the endometrium and sustain the pregnancy. However, there is some debate as to whether a little “LH activity” is needed, beneficial, or harmful in the follicular phase.
In the natural cycle, GnRH from the hypothalamus causes the release of both LH and FSH simultaneously from the pituitary, all through the stimulatory (follicular) phase and during the LH surge, so in the natural case, LH is always present while the follicles develop.
hCG and LH are almost identical molecules with the same biological effect, but the small differences cause LH to have a much shorter half-life than hCG. LH disappears quickly, while hCG lasts and lasts. Biologically, that makes sense.