I am20 weeks pegnant and just had my ultrasound done. I received a call from my nurse saying there was a shadow present in my baby s heart and that they want me to come in for more blood work and another ultrasound in a month. They tell me it s a soft marker and could be a birth defect. I m totally freaking out. What type of defect r they talking about. My down syndrome test during my first trimester came out negative. However, I am worried bc I do have an uncle who has down syndrome. Please help and clarify!!