Hi Claire , glad all was well with baby at scan
I had a slight placenta abruption they called it ,at 9 weeks with my second son, and apparently a tiny bit of placenta came away, quite common I think,but I did get quite oa bit of red blood which caused me to got to EPU in the first place, and it was fine, I had one bit of bleeding, and they said the remaniing pocket of blood would either get reabsorbed or come out naturally. Mine got reabosorbed, by the next scan time , so all was well, try not to worry. I did get some anti E antibodies because of this as blood from baby mixed with mine (somthing like that, and my body buiklt up antibodies to it, they just monitor these during pregnancy, no major issues.
What did the scan lady tell you about it ? will they see you again, or just look again at 20 week scan?