Webster's New World Medical Dictionary

menstrual irregularity
Abnormality in the nor-
mal menstrual cycle, which is about 28 days long.
Girls and teenagers may have menstrual irregularity
for a time following the onset of menstrual periods.
Some adult women also have irregular cycles. This
can be a benign condition, but it can also be due to
problems in the uterus or ovaries, including cancer.
Adults with menstrual irregularity should see a
physician to rule out disease or other problems. In
some cases, medication, such as birth control pills,
can be used to regulate a chronically irregular
cycle.
menstrual spotting
The presence of apparent
menstrual blood during the times of the menstrual
cycle when bleeding is not expected. Some women
have a tendency to bleed around the time of ovula-
tion, which occurs at about the 14th day after the
first day of menstrual bleeding. In other women,
spotting can be a sign of internal problems, includ-
ing fibroid tumors of the uterus. Although spotting is
usually benign, its onset is always a reason to see a
physician to rule out serious causes of the bleeding.
menstrual synchronization
A phenomenon
that occurs when two or more menstruating women
live or otherwise spend a lot of time together, in
which the menstrual cycles of the women gradually
become synchronized. The mechanism and reason
for this effect is unknown, although research sug-
gests that it may be due to the effects of female
pheromones on other women’s ovulation cycles.
menstruation
Bleeding that occurs each month
if pregnancy does not occur. Also known as menor-
rhea and menses. See also 
menstrual cycle.
menstruation, anovular
Menstruation that
occurs without ovulation. Usually in anovular men-
struation the egg that remains in the ovary simply
disintegrates, but in some circumstances it is fertil-
ized and a life-threatening ovarian pregnancy
results.