Amazing Cycle
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Our bodies are amazing things! The questions I hope this page answers are asked all the time, and just illustrates how much we are NOT taught about what happens each and every month in our own bodies. Most of the information was gleaned from the wonderful book Taking Charge of Your Fertility
by Toni Weschler. I have rewritten it all in (mostly) my own words but the book is an EXCELLENT source of information for any woman, and I can't recommend it highly enough. Any future daughters of mine will have plenty of exposure to this book well before they menstruate.

Hormones - not just for PMS anymore

Every month there is a remarkable dance of hormones in our bodies. A handy way to remember the hormones and the order they affect us during our cycle is:
Follicle Stimulating Hormone (FSH)
Luteinizing Hormone (LH Surge)
What does that mean? Well - every cycle your body (I'm assuming the reader is a woman - if not, deal with it *grins*) starts releasing Follicle Stimulating Hormone (FSH.) This causes BOTH ovaries to start maturing 15 to 20 eggs EACH. Each egg is encased in its own little follicle. These follicles produce estrogen, which is the hormone necessary for ovulation to occur. There is now a little race going on in your body - which follicle will become the largest.

The Myth - you ovulate on alternating sides

The Truth: You very well might - but you have a 50/50 chance EVERY month for ovulating on either side (unless there's some medical reason why you wouldn't.) The above mentioned race continues until the build up of estrogen in your body causes the most dominant egg-containing follicle, whichever side it happens to be on, to burst and release the egg. It is fairly arbitrary which ovary will do this - the myth of alternating sides is really just a reflection of the law of averages.
This means that you have completely redundant systems on both sides! Mother Nature was pretty clever! If you lose an ovary - you will STILL ovulate every month. This should be very good news to women who have lost an ovary - you're still basically as fertile (again, assuming no other related health problems.)
The race to ovulation is typically about 2 weeks, it can take anywhere from about 8 days to a month or longer to complete. The primary factor is how long it takes your body to reach an estrogen threshold. Stress can certainly affect this, by the way, so keep that in mind if you're trying to get pregnant (or avoid pregnancy, I suppose too!)

Another hormone - Lutenizing Hormone (LH)

All that estrogen, when it reaches that critical threshold, will trigger an abrupt surge of LH. It's the LH surge which causes the egg to actually burst through the ovarian wall - typically within a day of the actual surge. Many women feel slight twinges during ovulation, which has the bizarre name of mittleschmertz. This is a German or Yiddish (I'm not sure - anyone know? email me and let me know!) word meaning "pain in the middle." There are debates about what women are actually feeling at that point - if it's the egg bursting through, the follicles getting large ... you may or may not feel it - but it doesn't mean much as far as whether or not you are ovulating. Anyway, I'm digressing...

Fimbria - the quicker picker-upper

After the egg is released (ejected?) it is quickly swept up by the little fingers at the end of your fallopian tube, called the fimbria. This can take as little as 20 seconds to occur! It is most likely that that fimbria closest to the releasing ovary will pick up the egg, but again - you have completely redundant systems on both sides, and it is entirely possible that the opposite tub may grab it. If you only have one fimbria for some reason, it will do the work for either ovary. I personally know several women who are pregnant or who have delivered babies with an ovary on one side, and a tube on the other.

Corpus Luteum - a legal term, or a hormone producing lump

It's the lump thing - if you're ever served a corpus luteum by a process server, you're in big trouble (and gross!) No, seriously ... after the egg has been released from the ovary, the follicle that it was in collapses on itself (no egg inside to keep it firm and big) and becomes a little yellow body, or a "corpus luteum." It remains behind on the ovarian wall and starts releasing another hormone: progesterone. This does a bunch of things for you, which I'll get to in a moment. The corpus luteum is not long for this world - it has a definite finite life span of about 12 to 16 days. This rarely varies more than a day or two for any individual woman, but can vary between women a bit.

Progesterone - why do I need so many hormones anyway?

The release of progesterone is an important thing for your fertility! It does 3 things:
  1. Prevents the release of all other eggs for that cycle.
    Maybe twins sounds good - and within the first LH surge, you may well have released two or more eggs if they were all right at the edge of ready at the same time - but 15-20? I think I'll leave having litters to mammals that have the boobs to support them!
  2. Causes the uterine lining (endometrium) to thicken and sustain itself until the corpus luteum disintegrates 12 to 16 days later.
    You need that if you're going to be pregnant and sustain it. The fertilized egg will burrow into it, and at that point (see below) there are more hormone triggers to keep progesterone around - but before that, you need the progesterone from the corpus luteum to sustain any possible pregnancy!
  3. Causes the three primary fertility signs to change. That is, waking temperature, cervical fluid and cervical position.
    For more information about all that, I highly recommend the book mentioned above.

Why is my period a different length each month?

Maybe you're as regular as clockwork...but maybe you aren't always. So to point out what might not be initially obvious, the first part of your cycle, while estrogen is building up, can vary time-wise, and is possibly affected by all kinds of things in your life. The second, or luteal phase, is pretty much a set amount of time. Once you've ovulated, it's the corpus luteum that is going to determine when you get your period next - and it's sitting safely on the inside wall of your ovary, unaffected by the stresses of every day life.

Where's pregnancy fit into all this?

Gee, I'm so glad you asked! Well - after the egg is picked up by the fimbria, it has about a 24 hour life-span, unless it gets fertilized (woo hoo!) If that happens, there has to (obviously?) be sperm there for the egg - either waiting already, or on its way. With good cervical fluid, sperm can last and be waiting for up to 5 days! During your non-fertile times, sperm usually die within 12 hours or so. Amazing, huh?
Fertilization, if it occurs, will take place in the outer third of the fallopian tube, within a few hours of actual ovulation. It might be a few hours for a lucky sperm to get that far! The lucky fertilized egg will the continue to get pulled down to the uterus by vibrating cilia, little hairlike projections that line the fallopian tubes. This takes about a week or so and then the little egg can begin its burrowing process. It would of course be terrible for the endometrium to begin to disintegrate at this point because of a lack of progesterone (what usually happens to cause your period) so something amazing now happens. As soon as the fertilized egg burrows into the lining it starts releasing a pregnancy hormone, HCG (Human Chorionic Gonadotropin) which sends a message back to the corpus luteum left behind on the ovarian wall. HCG signals the corpus luteum to remain alive beyond it's usual maximum of about 16 days, which means it continues to release progesterone long enough to sustain the nourishing lining. After several months the placenta takes over this job as well as several other important jobs, of course.

HCG - hey - where else have I seen that?

Maybe on pregnancy tests? At home pregnancy tests look for this pregnancy hormone. Equate, the Wal-Mart brand is the most sensitive, able to detect and test positive at a level of 20. Others detect at 25, 50 or 100 ... so which test you get really matters on when you'll get a positive test from it. You build up HCG every day, so that's why waiting may change the results.

Myth breakers - in summary

So there are several things that don't seem to be common knowledge that I'd like to summarize.
You don't ovulate from alternating sides, necessarily.
It's a 50/50 shot each time.
You're half as fertile if you're missing the equipment on one side or another.
Because of the redundancy in our bodies, you probably aren't much if any less fertile. Three cheers for Mother Nature!
You have to time sex REALLY carefully if you want to get pregnant.
If you have pretty good cervical fluid, you could be romantic *ahem* Friday, and actually get pregnant while grocery shopping on Monday!
You learned everything you needed to know about your body in health class.
I doubt it - but hey, you never know! I sure didn't!

Supporting graphics

The Ferning of Fertile Cervical Fluid
When viewed under a microscope, the stretchy-type cervical fluid look like a beautiful ferning pattern conducive to sperm motility (left, above.) The drier, sticky types of cervical fluid do not have such a magical appearance (right, above.)



Copyright Kimberly Bobrow Jennery, 1997-2006

Contact Kimberly at: kimberly at bobrow dot net