Hi I Had An Ultrasound Done At 20 Weeks Pregnant

Hi I had an ultrasound done at 20 weeks pregnant and they found a little white spot on baby's liver. I had another ultrasound done at 29 weeks and the spot was still there. But they said my baby is growing like he should be and they see nothing else wrong. And heart beat has always been strong. There was only one spot on the liver and nothing no where else. But I haven't heard anything from my actual doctor yet as I don't have an appointment for 3 more days. What is/or could this be?