Potential Down Syndrome

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Guys, I’m freaking out a little..OB called me to tell me that there was a soft marker for Down Syndrome (short femur length). I had my anatomy scan this morning but it was kind of early (18 weeks along) so I’m wondering if my baby is maybe just small for his size and the length shouldn’t be reflective of the soft market?? Has anyone been told something like this? I’ve had no genetic testing done and first baby completely normal. I have a repeat US in 3 weeks.