Fluid in Kidney and Hole in Heart

This week at our 19 week ultrasound the doctor found a small amount of fluid on his left kidney and a very small hole in the bottom of his heart. He assured us that these are both very common and over 90% of the time fix themselves by birth. What worries me is that he wanted to do an additional blood test for chromosomal issues as these can be soft markers. Has anyone else dealt with this and have encouraging outcomes to share? I'm really worried about it!