Baby’s Head Measuring Small

I’m very concerned, just left my drs appt and the baby’s head is measuring very small compared to the rest of the body. I am waiting to hear from MFM for a level 2 ultrasound to be scheduled. Anyone go through anything similar (with either this or a previous pregnancy)? I have done all of the genetic testing possible and everything came back normal. Haven’t been anywhere with Zika since January 2018. Currently 24weeks 2 days.