I'm dont know what it was after one week, but I do know after two weeks I had lost 12kg. (I went from 97kg at week 39, to 85kg 2 weeks after birth)
Bear in mind that I put 40kg on during my pg.
It has taken me another year after Aidyns birth to lose another 15, so I am now down to 70kg, with still some to go...