Have been scanned fortnightly since 20wks as my baby has been measuring 2 to 3 weeks behind in measurements. up to this point all the measurements have been showing the same difference so they weren't overly worried Now reached 27wks to be told the head is starting to lag behind more and they may refer me to a specialist if it hasn't caught up in 2wks time. Haven't been completely confident in the hospital as I've yet to see my consultant just different registars who even through have my notes still want me to explain what the problem is and why I'm there? They all tell me that it's hard to get an accurate reading as every doctor measures slightly different and it could be just a small baby. My dh wants us to pay for a 3d private growth scan as he thinks this will be more accurate and will hopefully put our minds at rest. has anyone ever done this?