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Exercise in Early Pregnancy: Risk, Low Progesterone, and Miscarriage

Catherine McDiarmid-Watt | Monday, September 24, 2007 | 0 comments

QUESTION: I'm 7 weeks and I'm an avid runner. My doctor advised that I not run because of a low progesterone. I'm on "Prometrium." Why can't I run?

ANSWER: Strenuous exercise has long been associated with decreased amounts of progesterone. Marathon runners are famous for what is called "Exercise-related Amenorrhea" (no periods). No one quite knows why this is, but it seems related to ovarian production of progesterone.

Ovarian progesterone is made in the second half of the menstrual cycle, and it prepares the lining of the uterus for implantation. When pregnancy occurs, this "second half" of the cycle continues until term, when progesterone finally falls off. But there's a transition at the end of the first trimester, because at that point the placenta takes over the job of making the progesterone.

Progesterone will only be produced at appropriate levels after an adequate ovulation. If ovulation fails to occur, as in some cases of ovarian cysts, or if the egg ovulated is faulty, the residual ovarian tissue at the ovulation site (where the progesterone is made) will not make enough progesterone. This ovulation site, the "corpus luteum," is then labeled as inadequate. Women with an inadequate corpus luteal phase of their cycle never prime the lining of their wombs enough to have a legitimate period, and so periods are either late, scant, or unusual in color.

The faulty lining also poses risk for implantation, and miscarriage is a risk... theoretically. This is why doctors use progesterone to supplement those with "inadequate" progesterone. The level can be easily determined with a blood test. The Prometrium you have been prescribed is a natural progesterone -- identical to the very stuff your own body makes.

But is the baby in danger because the progesterone is low, or is the progesterone low because the baby is in danger? This is why giving progesterone is controversial, because some feel if it's low, it's always because miscarriage is inevitable. Others feel that giving the progesterone does no harm, except to perhaps delay an inevitable miscarriage by supporting a bad pregancy beyond the time it would have miscarried.

I myself give progesterone. I'd rather take a chance on delaying a miscarriage than writing off a baby that just might make it.

Back to your question:

Does exercise actually consume the progesterone made in some strange metabolic way? Or is there low progesterone because exercise affects the ovulation that is the necessary precursor of progesterone? In your case, I would say moderate exercise wouln't be harmful, especially since you're supplementing your progesterone anyway. But I'm not your doctor. Perhaps there are other concerns about your first trimester. Or perhaps your doctor has had a tough time getting your progesterone up even with supplementation.

When posed with questions about exercise in pregnancy, obstetricians feel one can resume any exercise regimen that she's already used to. But this answer is not polluted by a progesterone problem: When the progesterone's low, we're dealing with a phenomenon that's not completely understood. Certainly NOT running will do no harm. Your doctor doesn't want to worry about possible problems while worrying about known problems.

Note: The normal level of progesterone is usually "15-20." If the progesterone level is ~13 or so, this is seen as salvageable. If the progesterone is <5, I've not really seen progesterone do any good.

©2000 GERARD M. DiLEO, M.D., F.A.C.O.G.

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About Catherine: I am mom to three grown sons, two grandchildren and two rescue dogs. After years of raising my boys as a single mom, I remarried a wonderful man who had never had a child of his own. Unexpectedly, I found myself pregnant at 49!
Sadly we lost that precious baby at 8 weeks, and decided to try again. Five more losses, turned down for donor egg, foster care and adoption due to my age and losses - we have accepted that there will be no more babies in our house.

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