yes it is very common. a friend of mine had ultra sounds all during her pregnancy and no one knew she was having twins until she gave birth to 2 kids... so it is very possible. Also my mother is a twin and no one saw her or herd her heart beat until 7 months into the pregnancy so the answer to this question for me is yes a twin can hide during pregnancy.
A gemellar pregnancy is a twin pregnancy.
Depo Provera shots do not effect the results of home pregnancy tests, nor do they "hide" a pregnancy.
Yes, there is a condition called 'Vanishing twin syndrome'. This occurs when a twin disappears in the uterus during pregnancy as a result of a miscarriage of one twin. The fetal tissue is absorbed by the other twin, multiple, placenta or the mother.
The dead twin will be still-born and will have not effect on the remaining twin. You do need to speak to your OBY/GYN for more detailed advice.
Twins are by definition TWO. Any other number and it isn't a Twin birth. There's a considerable random element to Twin pregnancies, so there's no actual limit to how many Twin pregnancies a woman can have during her fertile years. Any pregnancy can be a Twin pregnancy.
Anxiety related to twin pregnancy
TWin to twin tranfusion syndrome.
A singleton pregnancy has only one embryo; in contrast, a twin pregnancy has two.
He's probably having a Sympathetic Pregnancy. He feels bad about his sister suffering during her pregnancy, so he's subconsciously displaying pregnancy symptoms in hopes of making her feel better. It's all in his head, he's NOT actually pregnant.
Unfortunately there are several reasons contributing to cramping during pregnancy. They can be due to gas, constipation, implantation bleeding, ectopic pregnancy, miscarriage,vanishing twin syndrome, or pre-term labor.
To hide that you are pregnant.
Vanishing twin syndrome was first recognized in 1945. Vanishing twin syndrome is when one of a set of twin/multiple fetuses disappears in the uterus during pregnancy. This is the result of a miscarriage of one twin/multiple. The fetal tissue is absorbed by the other twin/multiple, placenta or the mother. This gives the appearance of a "vanishing twin." http://www.americanpregnancy.org/multiples/vanishingtwin.html