sonographer asking about bleeding

Hi all,
I went for my 20 week scan today which was all good.
Whilst having the scan she told me the placenta was high anterior. She also asked me if I had had any bleeding which, at the time, I told her I had not since my last period and that was that.
After I came out I began to wonder why she had asked and whether she had seen something bad. She didn't say anything at the end about it but it's now got my mind working overtime.
Anyone know why she may have asked something like that?
TYIA x