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Discussion Starter · #1 ·
I'm curious why there is only a 20% chance of conceiving each month in healthy adults with no fertility problems. I learned about that a few months ago--before that I thought if the woman is ovulating and the man's sperm is fine then if they bd anytime within 3 days of O they should get pg. What causes that not to be true? We've had 2 months this year of unproteced bding around O where we didn't get pg. Last month it was 3 days before O, 2 days before O and the day of O. I've never had any trouble with my other 2. I didn't chart my temps this cycle but I did chart my cm and by when I had AF, I was right on with my cm. I just don't understand why we wouldn't conceive...
 

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Well, eggs are only good for about 12 hours after they come out, first off. So all those spermies that are hanging out waiting for the egg only have that long to breech the outer defenses. Now, while (typically) only one sperm can fertilize one egg, it takes several hundred sperm trying to penetrate the egg for that one sperm to get through. Also, it's not like eggs have a sperm magnet, the sperm are pretty much just swimming blindly upstream. Some end up going up the wrong fallopian tube, others try to fertilize random bits of your uterus, some just die off out of weakness, it's rather like salmon only with far less spawning at the end.

Okay, so odds are already below 100% just getting enough sperm to the egg during the right timeframe.

Then we add in implantation which, as all sufferers of short luteal phases know, can be a problem. Even with all the right hormones going and a nice cushy uterine lining the fertilized egg could just not implant. Or it could implant some place where there isn't enough lining to support it. (That's right, with most of the uterus putting out fresh flowers and "ZYGOTE WELCOME HERE!" signs, sometimes the silly thing decides to just set up camp on a barren field.) I'm not sure if ectopic pregnancies are counted in the 20%, I'd guess not, and they'd be another example of implantation just plain not happening correctly.

Meanwhile, there's still the whole division of cells to consider. Sometimes the ovum simply doesn't. Sometimes it starts to and the little self-checks go "whoops that's the wrong shape for that chromosome!" and the whole project spontaneously aborts.

Interestingly, your chances of conceiving on any given month also decrease steadily as you age. I, at 25 nearly 26, have a lower chance of conceiving than an 18 year old. A 30 year old has less chance than I do, and so on and so forth. Fortunately, it's a gradual drop, however, it does explain why many women have no problems conceiving that first baby, but have a great deal of trouble TTC#2.

Anyway, that all adds up to "yeah, but why aren't *I* part of the 20%?" and the answer to that would make me rich.
 

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Discussion Starter · #3 ·
Wow! Thank you so much your reply! That helps so much. I'm 26 and starting to feel like I was a lot more fertile at 22 when I got pg on the first try with DS1! DS2 technically took 2 cycles (first was a chem. pg) and now here we are.
 

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There can be the occasional cycle when the egg doesn't make it into the fallopian tube. Those swimmers might be hanging around and waiting to no avail. Women occasionally have a cycle when they just don't ovulate.
 

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This may not be that helpful, but there's a great PBS special on the whole process that makes you realize just what a miracle any conception is... and naturally, I can't find the link or remember what it's called. Can anyone help?
 

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Ditto the above, said so much better than I could have put it. There's just more to this whole process then sperm meeting egg.
 

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Quote:

Originally Posted by Jenn_wants_3
I just wanted to say that was beautifully explained. I never saw anyone put it so ..... clearly.
:

Exactly what I was thinking when reading. I always need a refresher on certain things ... and your passage was so informative and nicely put!

Thanks
 
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