it is possible to carry a baby full term with this condition. as an l&d nurse, we see it a lot. the only thing is, you can not have a vaginal delivery. the baby must be delivered via c-section. you will probably end up on bed rest if it is a true previa. if you bleed more than what a panty liner can handle, you need to call your doctor immediately. also, anything in the vagina is not allowed! this includes sexual intercourse, sorry! hope this helps :)
I had the same thing and at about 28 weeks, mine also shifted when my baby had a big growth spurt. I never had any cramping or bleeding either. I did, however, have a friend with it that never shifted and she had a successful pregnancy with a c-section for delivery and her and the baby were completely fine. She even went over due!
I had a low lying placenta at 20 weeks also and baby was already head down didn't have any cramping or bleeding. Had another scan at 28 weeks and my placenta had already shifted. If your doctor didn't make a big deal out it I wouldn't worry because from what my dr told me the worst could be that I would have to have a c-section. As long as you are bleeding or cramping you should be fine.
I had a low lying placenta, but mine never covered the opening of the cervix. Did your doctor specify what yours is doing? There are different cases, and each require different answers. For example, marginal is where it is close but doesn't cover. Partial is where it's half covered and a complete fully covers the opening. If the uterus doesn't move or completely covers the opening, you will need to have a c-section done as baby can't be birthed vaginally. In many cases however, it does move. Mine was discovered at my 20 week scan, and by my 24 week scan it had moved up enough. I never had any form of bleeding or spotting. I cramped, but that's to be expected and is normal.