Anomaly 20 week baby scan?

My sister in law went for this scan today where they said the couldn't see the babys bowel, so she has to go back and have another scan Tues. To start with they couldn't see the spine, so she had to have a second scan again they couldn't see it so the doctor was called in who said, it was just the umbilical cord covering it, so again she had to wait abit and have another one, this time the spine was visable but no bowel, what could this mean? After 3 scans in one day, but not to be able to see the bowel on them?