Re: Why does Menstrual blood not clot?

The answer to your question of "what's the reason behind  menstrual blood 
not clotting" is put very simply. Normal menstrual blood does clot, 
menstrual blood contains not only blood but also tissue from the lining of 
the uterus.
The hormones estrogen and progesterone  make the eggs in the ovaries 
"mature" and prepares the uterus for pregnancy. Once a month, one egg 
matures and leaves one of the ovaries, heading down one of the fallopian 
tubes toward the uterus. During this time, while the egg is traveling, the 
uterus begins to build up its lining with extra blood and tissue, making 
the walls of the uterus thick and cushioned. If the egg reaches the uterus 
and is 
fertilized by sperm, it attaches to the cushiony wall of the uterus, where 
it uses the extra blood and tissue to nourish and protect itself as it 
slowly develops into a baby. 
In most cases, though, the egg isn't fertilized by sperm, and is just 
passing through instead. When this happens, the egg dissolves and the 
uterus, no longer needing the cushioning for the egg, sheds the extra 
tissue lining. The blood and tissue leave the uterus, going through the 
vagina on its way out of the body. This is a menstrual period. This cycle 
(an egg being  released once a month and the uterus building itself up and 
then shedding its lining when it's 
not needed) will happen almost every month for several more decades - until 
a woman no longer releases eggs from her ovaries. http://www.gynalternatives.com/causes.htm 
To answer the second part of your question ,"Are there any blood coltting 
factors missing in menstrual blood?"
There are several conditions where blood clotting factors may be missing 
but I am only going to refer to one of them which is the most common 
bleeding disorder in women and girls.  It is called von Willebrand disease, 
an inherited disorder that affects up to 3% of the population, or  
approximately 2.6 million people. Half of these people are women.
Von Willebrand disease is caused by a defect in or a deficiency of a blood 
clotting protein called von Willebrand factor. von Willebrand disease 
causes bleeding into the skin and from mucous membranes, which line the 
nose, gums and the gastrointestinal and genitourinary tracts.
Symptoms of von Willebrand disease include frequent or prolonged 
nosebleeds,easy bruising, bleeding gums, bleeding following dental work, 
and heavy menstrual periods.
There is no cure for von Willebrand disease, but it can be treated. Minor 
bleeds may not need treatment, but more serious bleeding problems (such as 
very heavy menstrual periods) can be regulated by taking birth control 
pills or other hormones. http://womenshealth.miningco.com/msub31.htm?TMog=62829403091525 http://biomed.redcross.org/home/cmponent.htm
Check out the internet sites I have included I am sure you will enjoy the 
references. I want to thank you for taking the time to send in a question 
to the MadSci Network and I hope I have given you enough information 
concerning your question.

June Wingert RM(NRM) ASM
Center of Comparative Medicine
Baylor College of Medicine
One Baylor Plaza
Houston, Texas