I have to totally agree that using DS is a "one shot" deal. My RE doesn't do b2b IUI in any case as she ran a study at OSU and determined that there isn't a significant increase in BFP in b2b IUI over "one shot" IUI.
I also have to second the motion of using a fertility medication (Clomid or Femara) even if you ovulate with no problem. I too ovulate just fine, but got a BFN on my first un-medicated IUI. Because of the cost of DS, and the fact that I'm ready to be a mom, I'm not doing unmedicated again. I'm using Femara (Clomid is off the table as I'm a migraine sufferer), to help increase the # of follies so maybe I can increase my shot at getting preggo.
On a side note, DS can have higher #'s at times. Our DS had a count of 73 million with 60% forward progression. My RE was very excited (so were we). I'm hoping to have the same or similar counts this time around too.
Good luck to us all and hopefully the

is on the way for all of us!
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ME: 27 No known problems (we're hoping to keep it that way)
DH: 28 Azoo due to Chromosomal issue
4/21/09 - First consult with RE - ultrasound shows things look good
05/01 CD 2 bloodwork - all clear and happy!
05/5 HSG = 2 beautiful, open, tubes! YEA!!
05/20 Progesterine check - 17.8 WHOHOO!! We're in the game to start IUI!!!
1st IUI: 6/12 - unmedicated
73 million/60% progression :
2nd IUI: 7/9 - 5mg Femara (2 follies R:21 L:22)
48.3 million/42% progression: