Try:
Code:
Sub CellMerge()
Application.ScreenUpdating = False
Dim Tbl As Table, Rng As Range
For Each Tbl In ActiveDocument.Tables
With Tbl.Rows(1)
If .Cells.Count > 2 Then
Set Rng = .Range
Rng.Start = .Cells(2).Range.Start
Rng.Cells.Merge
End If
End With
Next
Application.ScreenUpdating = True
End Sub