Femur length

Hello,

I am pregnent. I am on my 29th week. The femur length is 49mm. The doctor said that the growth of the femur is 3 weeks behind the normal. All the other mesurments are normal. We haven't done amino because we were obliged to concive our baby through IVF and the risk of Down syndrome was 1/303 where as the risk of miscarriage was 1/100. And now the femur length is shorter than the normal. I am 4"11 and my husband is almost 5"10. Some say that as I am not so much tall it's normal, but what is the reality, can somebody suggest me and help me please. Is there any risks for the baby to be disproportion. What will be the consequences of the femur length.
Thanks