Long bones are measuring 3 weeks behind

My sister had her anatomy scan a few weeks ago. My nieces arm and leg bones were measuring short. She saw a fetal specialist today. They told her they are measuring 3 weeks behind. Everything else is measuring on point for 27 weeks. She is 27 weeks today. They are calling it skeletal dysplasia. They did

IVF

and I was her egg donor. So all the genetic testing was done before. Also she had genetic testing done at 9 weeks. We were looking to see if anyone has had this before?!