we've been through lots of assisted conception and never advised not to DTD in the TWW - in fact we've had the opposite where we WERE advised to do it!

in all honesty, if you're not trying to get pg, you wouldn't even think of the TWW and would just do it when you want - and it doesn't impact the chances of unplanned pg at all!

FWIW - i've been through 11 assisted conception cycles - due to hubby being away for some of the TWW, we didn't dtd - but in each of the four that took we DTD at least a few times - and for this one, he was home for 8 of the 14 days, and we just went with the flow (the hormone drugs can make a girl VERY playful!) and it had no dire consequence for us!

i read somewhere, can't remember where, that DTD helps somehow with encouraging implantation - would love to remember where i read it though!