With my first pregnancy we declined the 12 week us beacuse i was young and healthy and wouldn't terminate if downs was an issue, and then when i got to the 18 week us we discovered my son had severe organ abnormalities which MAY or MAY not have been able to be detected at 12 weeks. I had to terminate at 18 weeks as his organs where not formed to an extent that no surgery or help could be done to save him, he has severve renal (kidney) problems and this had caused him to retain fluid and that fluid went pretty much straight to his brain and his enlarged kidney (only one) had caused his bladder and stomach and heart to be deformed.
He was still alive at that stage, however he was dying, and would have definatley died at some stage before birth and rather than wait we terminated then. I had to birth him as i was 18 weeks, and i guess part of me felt at the time that maybe, just maybe if i had have had the 12 weeks scan, we could have picked up on something and either something could have been done, or i may have terminated then by D&C and not had to give birth, which was unbeleivably traumatic for me.
I have since had a few early m/c which i never got to the 12 week mark to have a scan, and then my daughter who i had a date test (9 weeks), then the 12 week NT, then the 18 week where we discovered i had a single vein single artery umbillical chord, you are supposed to have two veins i think (which is apparently often a sign of possible kidney problems, but they were ok this time, i had a perfect chord with my son) so the dr recomended a 32-35 week scan to check for growth, which i had at 34 weeks and 6 days and the dr picked up on a bleed on the placenta which had formed a clot and sent me home only for the clot to break free 24 hours later and cause a placental abrubtion which caused me to loose my daughter.

I guess i am trying to say, even without u/s things can go wrong, and even when things are wrong and you have an us things STILL dont always go right.

I am pregnant again now and i have had one scan at 8 weeks and i will have another at 12 weeks, and then being "high risk" i will have weekly ctg monitoring and possibly more scans if anything looks hairy (definatley NOT with the dr who picked up on a bleeding clot and sent me home!!!) and just hope and prey that it all goes well.

I will also be camping out near the hospital from about 30 weeks LOL just incase i feel funny, i am only two minutes away from the hospital rather than 45 minutes!!