Worried About Ultrasound Results

Hey everyone! Just need some words of peace. I got an ultrasound at 8 weeks 4 days, baby was perfect! Measuring exactly on time etc. However, today I got a call and they want me to come back for another scan at 13 weeks. They said they saw some extra tissue near the bottom of uterus. What could this be?

I have one other child, 15 month old daughter, who was born vaginally (I was induced because she was too small and my body wasn’t giving anymore nutrients in the womb, and I did tear)

So could the extra tissue be scarring, a possible cyst, missed twin?? They obviously don’t think it’s extremely urgent because I’m waiting another month but I’m curious and a little worried since last prgancny had complications too