We are still working towards the timing of the hCG shot, but we first need a little more background. We need to go over difference between the natural LH surge and the hCG injection.
After LH leaves the pituitary during the surge, it causes the ovulation by landing on specialized spots on the ovarian cells, the LH receptors. All hormones act by landing on (binding to) their specific receptor, and usually one hormone does nothing if it lands on the receptor of a different hormone. There has to be a match.
This is usually dictated by shape. It’s like a lock that recognizes the shape of the key. FSH and LH are similar hormones, but their shapes are a little different. So if LH comes across a FSH receptor, it would not bind.
There is a notable exception. Because hCG and LH are chemically very similar, with very similar shapes, hCG can bind to the LH receptor, and can do it well. Since hCG can land on the LH receptor, hCG can do the same job as LH.
This is actually very important to pregnancy. Pregnancy needs progesterone, which comes from ovarian cells with LH receptors. So LH causes the ovary to make progesterone after ovulation. Good: the progesterone allows the embryo to implant. Then the embryo makes hCG. Better: this causes the ovary to make even more and more progesterone which keeps the implantation going strong. Both occur via the LH receptor.
That hCG can behave like LH is good for treating fertility patients because we can cause ovulation with an injection of hCG instead of an injection of LH. This is good because hCG is easier to get than LH.
So why not just give LH? Up until very recently, LH was not available. Years ago the only way to get FSH for our fertility drugs was to extract it from the urine of menopausal women.
(This is a whole story by itself. Initially, starting in the 1970’s, the urine was obtained from menopausal Italian nuns who would leave jugs of pee for the drug company Serono to pick up in the mornings. Menopausal women have really high amounts of FSH in their blood, and most of it comes out in the urine. The pee would be taken to a factory with a swimming pool-sized pee vat, and they would somehow get the FSH from the pee. Serono went on to be the most profitable company in the world. The Catholic Church was rewarded for its cooperation. Even today, pee swimming pools exist for companies who make fertility drugs from urine.)
Because FSH and LH are similar molecules, the methods used to pull out the FSH grabbed LH too. Once we got the FSH/LH mix, we didn’t have the science to separate the two. So we could not get enough pure LH to cause ovulation. Today we can get pure LH made in a lab, but still in small amounts, not enough to get a good ovulation going.
How do we get the hCG? That is piece of cake, we get it from placentas. There are tons hCG in placentas and it’s easy to extract. Today hCG is also made in a lab, that’s the Ovidrel. It’s pure stuff, and that’s why it can be given in the skin. The placental hCG is given IM because it’s contaminated. hCG is also a protein, and the system for extracting the hCG protein from placentas is pretty crude, so tons of other placental proteins get caught in the net too. These extra proteins can cause a local allergic reaction when given in the skin, but not when given in the muscle.
When we used to get fertility drugs from urine, same thing, they had protein contaminants and needed to be given into the muscle. Recent exceptions are Menopur and Bravelle. These are from urine but using new systems that are better at cleaning out most of the unwanted contaminating proteins. Gonal-F and Follistim are both made in the lab and do not have the contaminants. They are given into the skin.
Today there are 2 products, placental hCG given in the muscle, and the lab-made hCG given in the skin. The placental is still cheaper and words great.
In a cycle stimulated with injected FSH (for IUI or IVF), most of the time the natural LH surge does not occur at all, so we need to give the hCG. In some cases the LH surge does occur, but it happens too soon, before the eggs are mature. This is probably due to the fact that estrogen levels are higher earlier in a medicated cycle, so the LH rises earlier. We don’t know why a premature LH surge only happens in about 20% of cases.
The bottom line is that we cannot count on the natural surge to occur at all, or at the right time, when we are using FSH injections. We need to use the hCG injection for proper timing of ovulation and proper timing of the egg retrieval.
That’s it for now. Next time we finish up by talking about the right time to give the hCG shot.
"In a cycle stimulated with injected FSH (for IUI or IVF), most of the time the natural LH surge does not occur at all, so we need to give the hCG. In some cases the LH surge does occur, but it happens too soon, before the eggs are mature. This is probably due to the fact that estrogen levels are higher earlier in a medicated cycle, so the LH rises earlier. We don’t know why a premature LH surge only happens in about 20% of cases. "
I'm trying to understand what this implies. Let's say a woman gets an LH surge on her own (on a cycle medicated by clomiphene) and takes the HCG injection the following evening. Will the injection override the natural LH surge and cause the woman to ovulate 36-40 hours after the injection- regardless of when the natural surge began?
I am wondering because this is my current situation. Thanks!