White spot (calcium spot) on heart!

I had to see a high risk doc yesterday. She said the normal weight for baby at 18wks is about 8oz and says my baby boy is 9oz!  Also, I didn't do any of the genetic testing in the first trimester, but the HR Dr yesterday said she saw a white dot on his heart which is a calcium spot and is a marker for Down syndrome. She said not to worry, she sees it everyday and it almost always goes away. Anyone else have this happen?  I did a blood test to see if he's okay and will get results of that next week.