I think there's no special event for this purpose. But you can detect
with simulating a special "row counter"
if you can, in any column of your last row (after the last used row)
insert a cell with the formula "=ROW(A12)"
(if the cell is in the cell A12, this mean the line 12 is after the
last used one) Give a special name to that cell (example: "last_row")

Since each time you insert a line, the value of this special cell will
change, then a calculate event will occure !
Wone !

in the sheet events:

Dim old_last_row As Double

Private Sub Worksheet_Calculate()
with Me.Range("last_row")
If .Value < old_last_row Then
'nb of rows changed
old_last_row = .Value
End If
end with
End Sub

there are for sure many ways to do this, but you need to detect this
event from another one, since there's no special event launched when you
insert a line.