What Do This Ultrasound Test Result Of Fetus For Trisomy 21 Indicate?

We are adopting a baby. We received an ultrasound report. It states the humerus and femur are 2 SD below the median. Estimated fetal weight in the 8th percentile. No other anomalies were noted. It said it could indicated Trisomy 21, skeletal dysplasia or be normal for this fetus. How likely is it that this baby will be born with Trisomy 21 or Dwarfism?