I continued working out until it made me uncomfortable, which was 7 months. Everyone is different. Some women go the entire preg. Cardio should be fine the whole time (in fact, it's recommended), but I'm not sure about the ab workout...
Pregnancy brain wrong work lol .. depends on your workout I know some that worked our until their due date also. She ran the morning she went in labor even.
Not sure about working out but I know a lot that worked up until they went into labor so that they could have more maternity leave with baby. If they didn't go until they went into labor they usually went up until a week or 2 before their due date.