20 week scan call back

It's possible the sonographer wanted to check with the consultant before telling you, but they're likely double checking the attachment of the placenta. If you have a low placenta and previous caesarean section, there's the small risk the placenta might be attached to the scar, but this is pretty rare. Some guidelines would want the consultant to re-do the scan if the placenta is low and you have previous caesarean for this reason. The sonographer likely wanted to ask them if they wanted to see you, and that's what they'll check. I know it's scary, but don't panic before knowing anything, cause sometimes rechecking is just the rule to be safe, it doesn't mean it's definitely on the scar! And if it is, they'll explain everything to you!