Why do some pregnant women think they get a period?

Question

Especially when it's medically impossible to get a real period while pregnant since it's the shedding of the endometrium (uterine lining) necessary for pregnancy? I just keep hearing women say they had their period during their pregnancy and I have to wonder if they no idea what a period really is and what causes it. (Keep in mind that I do know that spotting due to other reasons is possible during pregnancy. It happened to me during my pregnancy.)

Here's the literal definition of menstruation (from http://www.m-w.com/dictionary/menstruation):

Main Entry: men·stru·a·tion
Pronunciation: "men(t)-strü-'wA-sh&n, men-'strA-
Function: noun
: a discharging of blood, secretions, and tissue debris from the uterus that recurs in nonpregnant breeding-age primate females at approximately monthly intervals and that is considered to represent a readjustment of the uterus to the nonpregnant state following proliferative changes accompanying the preceding ovulation.

Also, a medical article about menstruation:
http://www.healthline.com/galecontent/menstruation-1

Answer 1

Some women spot during the first month of pregnancy, as you noted. A small amount of blood is shed, and if they don't normally have a heavy flow, they think they had a small period. This is most common in women who are very slender, or who have been on birth control pills that were too strong.

Some pregnant women have a lower progesterone level, and that can lead to some menstrual flow during pregnancy. If the level is low enough, the body may not retain the pregnancy. (My mother had this happen 3 times back in the 60's, losing 3 babies between 3-6 months.)

Answer 2

Its obvious that these women only have a light period,a friend of mine started putting weight on and struggled to shift it where she eventually went to the doctors and found out she was 7months pregnant, needless to say she went into shock as she was having a period every month.

Answer 3

Perhaps it is not menstruation, per se, but women do bleed aside from implantation and miscarriage. I'll see if I can find a medical article about it.

Answer 4

its true that you can;t have a "real" period while your pregnant, but some bleed on the same schedule as they did before they got pregnant, so they just call it a period....pretty much semantics the way I look at it.

Answer 5

well i dunno about everyone else but my step sister gets 2 periods every month very few women get this i forget what its called and the statistics but it is possible she got her period every month during her first pregnancy and she didn't even know she was pregnant till she felt the baby kick