Pregnant after 5 day embryo transfer

My wife and I just went through our shared maternity cycle and did a five day fresh embryo transfer.  On the 20th we went in for an Hcg test and my number was 596.  Yay!!  Pregnant!!  Two days later I went back in and it was 4766.. Eeek!  Our doctor thinks it's most definitely twins (in his words, at least twins!) my wife is a twin so she is thrilled.  Twins is slightly scary for me but I'm over the moon either way.  Triplets scare me though!!!!  We still get the pleasure of both progesterone shots and suppositories until I believe ten to twelve weeks.  We go in for our six week ultrasound on Friday sept 4th.  I'm dying to know!