I can see her point of view to be fair, a 1.5 day period and a month where we DTD once and a regular cycle where we did more like 7 or 8 times ( were too tired for this every day malarky!) Which one is going to seem more likely? She's airing on the side of caution I think because if she takes me as being 9 weeks and sends me for my NT scan when I'm 12 weeks by that calculation, I could be a good 2 weeks out of the gestation bracket for the testing. Where as if I go next week and I am only 9/10 weeks, no harm done just rebook the NT scan based on that. So it does make sense.
Just a very odd feeling!
Edited to add: no I didn't do a test with weeks on, well, I did but they were both faulty and errored on me so by the time I got replacements from clearblue I was around 6 weeks so seemed pointless taking them!