There doesn't seem to be a lot of scientific evidence for an accurate assessment to be made. 

like the issue...good sub-topic.

here is some evidence that is on the yes side, but barely.

Inversion Confusion

Is it safe to go upside down when you're having your period?

By Timothy McCall, M.D.

Most yoga students are accustomed to hearing their teachers ask whether anyone is menstruating before leading the class into inversions. In many styles of yoga, such as Iyengar, doing inversions during your period is considered strictly verboten. Yet not all teachers consider menstruation an absolute contraindication to going upside down.

From a yogic perspective, the reason for not inverting during menstruation has to do with apana, the hypothesized downward pranic force that is said to help facilitate things such as bowel function, urination, and menstrual flow. The concern is that reversing this normal energetic movement could interfere with the period, leading to a cessation of flow and possibly heavier bleeding later on.

It may be wise to avoid inversions while menstruating. But from a medical standpoint, the belief is based mostly on speculation. Women are often warned that if they invert during their period, "retrograde menstruation" could occur. That is, blood could flow in the opposite direction and lead to endometriosis, a painful condition in which small clusters of uterine cells grow in the abdominal cavity. One study, however, found that retrograde menstruation naturally occurs in 90 percent of women, most of whom never develop endometriosis. So we do not know for sure if inversions increase retrograde flow or whether the backward flow increases the risk of endometriosis.

Here's my take on the situation: During class, if your teacher doesn't think you should be inverting, you ought to comply with her wishes. What you do on your own time during your personal practice, however, is your business.

i think that this issue should stay in this sub topic area, and i vote to move the issue regarding whether it is safe for pregnant women to practice yoga to this sub topic area too.

it is a tough call, to be honest, but it seems to me that for both issues the questions are about the health of women doing a certain activity, the focus is on the health of a woman. the issues in the yoga sub topic area i think should be focused more centrally on the activity of yoga. hope i am being clear here.

do others agree?

Does everyone agree this belongs under here vs. topic-Yoga?

issue prior to revisions:

This issue moved from another topic. The original issue can be found here

Okay, here we go...

Sure. (But if this issue is moved under the proposed new subtopic "Sexual and Reproductive Health," then we'd want to reword it to " ...practice Yoga inversions..." since it will no longer be under "Yoga.")

ok

I think we should move this to Women's Health, but we are still in the process of developing subtopics in that topic. Why don't we hold off on this for the moment?

Good revision.

issue prior to revisions:

thanks for the catch, elyse.  here's the problem.  the affirmative:

Women should do inversions during menstruation.

these are the affirmatives that make esperanto's blood boil ....  (whoops ... no pun intended.)

anyway, that's why i went with avoid.  i'm fine with "avoid". it's where the issue lies.  some will say women should avoid and some will say they should not.

this issue seems okay to me, but i would modify the wording a bit, in two ways.
first, i would remove the word "avoid" so that the issue becomes less biased.

second, i would change "menstrual cycle" to "menstruation."
seems that the issue in yoga is about whether a woman should do inversions during their period.

can't believe i am doing research on this, but anyway...

"menstrual cycle" refers to the entire 28 (or so) days. see below from wikipedia.

Menstrual cycles are counted from the first day of menstrual bleeding, because the onset of menstruation corresponds closely with the hormonal cycle. The menstrual cycle may be divided into several phases, and the length of each phase varies from woman to woman and cycle to cycle. Average values are shown below:

Name of phase	Days
menstrual phase	1–4
follicular phase (also known as proliferative phase)	5–13
ovulation (not a phase, but an event dividing phases)	14
luteal phase (also known as secretory phase)	15–26
ischemic phase (some sources group this with secretory phase)	27–28