Women do not menstruate while pregnant. If you are certain you are pregnant, and begin bleeding, you should see a doctor immediately.
Yes, Menstruation can also occur while pregnant, unless if she has menstruation disabilities.
No, it's biologically impossible for a woman to menstruate while she is pregnant - a woman will only menstruate if she doesn't get pregnant during the last cycle. A woman can bleed during pregnancy for various reasons but this is fairly rare, chances are if you're menstruating you're not pregnant.
Menstruation is body getting rid of the egg. If the egg is fertilized, the woman is pregnant, the body will not get rid of it.
I assume that you mean menstrual cycles, and no a person cannot have menstrual cycles while pregnant. It is biologically impossible to ovulate and menstruate while pregnant, the body shuts down the menstrual cycles once you're pregnant. People can bleed while their pregnant for various reasons, for example hormonal imbalance or implantation bleeding, but not menstruate.
If a girl thinks she is pregnant that doesn't mean that she is pregnant. A woman cannot menstruate while she is pregnant, thus if she menstruates she obviously isn't pregnant even if she thinks otherwise - although women can bleed during pregnancy this is uncommon, and not menstruation.
Some women have bleeding while pregnant that they think is their period, but bleeding while pregnant is NOT normal and should be evaluated by an OBYN!
No women fail to menstruate. It comes naturally.
Some cases have shown that some women have had period like symptoms while pregnant
No, not every female gets her period. If talking exclusively of those who are biologically female there are those who don't have the anatomy to menstruate or their bodies don't produce the hormones needed to have a menstrual cycle. Pre-pubescent girls don't menstruate and women past menopause don't menstruate, also women who are pregnant won't menstruate during pregnancy (sometimes for longer if they breastfeed), and women who have a hysterectomy to remove the uterus.
Some women still experience monthly bleeding while using birth control.
In fact, a majority of women may miss one period or so, but can still have regular menstruation cycles while pregnant.