SDhoegal, I would contact the centre that you are to have the u/s. They will know far more than the gp.

Why the u/s centre said it may be too early is because if your dates are out a bit this could make it too soon for an accurate result.

Most if not all fetal medicine units will ask that the bloods are done a day or two before the nt u/s. This is so on the day you will have a full result. Many u/s centres don't do this. They give you the result of your nt u/s and then phone or send the results of your blood test combined with nt u/s combined risk.

It is confusing - especially when different places do it at different times. It is my belief that 10 weeks is too early for the bloods to be done prior to a 12 week u/s. For best results the bloods should be taken as closely as possible to u/s.

Good luck...