White spot on heart?

At my 20 week anatomy survey, they found a small white spot on my little girl's heart. The doctor told us that it wasn't anything to worry about, that even he really isn't worried about it. He just wants us to come back in four week later for another scan just to check on it. I wasn't really worried about it until I ready that a lady had the same thing happen and her baby had downs. Neither my family or my boyfriend's family has ever had a baby born with any kind of genetic or chromosomal disorder. What is the likelihood of our daughter having downs? Has anyone else has this happen?