Had 20 week scan today. All looked good but needed cervical length scan due to previous caeserean at full dilation and have preterm birth clinic appointment next week. Measured at 29mm (did spot a measurementof 35mm prior to this but this is the one written on my notes). Sonograher seemed happy with this. I have obviously googled and it looks like I should be nearer 40mm at this point. Any experiences of this ?? Xx