Irregular fetal heartbeat :/

Hello ladies! 19 and a half weeks today, baby has not been well. Today I got really worried about my baby as his movements were like non existant all day, so I went in my local maternity triage to get checked out. The midwife found that my son has really irregular heartbeat, it was a good rate but it would skip beats alot, she was very serious as this could be a sign of heart defect or it could probably ease out till birth. I have a anomaly scan tuesday so I'm so over the edge on weather it's alright or not. :( I've been very distraught, this is my third baby, my first experience that baby might be very unwell. For now they will wait till scan and I should be extra cautious about feeling baby move and ringing them if anything changes. Has anyone had this with their babies? How did it turn out? Feeling so helpless and hoping for good news on tuesday :( thanks for reading!