It's a difficult situation because I've seen it all ways--
False positives: Baby's fine, mother spent time worrying unnecessarily, changed birth plans, all for what ended up to be no reason.
False negatives: I've seen anomalies so great that you have to wonder if the person doing the ultrasound had their eyes closed (I'm talking about a baby where 3 out of 4 of her limbs were malformed/ almost missing, had no kidneys or bladder).
And, mostly, positive positives-- the u/s was right on, there was a problem requiring intervention and treatment.
Heart defects are particularly tricky because there are different levels of fetal echos available and unless you have a "risk factor" then you often aren't referred for a higher level scan (
here is an interesting website that talks a bit about this). I can't tell you how many times, during my 3.5 years in the NICU (and occasionally floating down to the Pediatric Cardiac ICU) I saw babies with major heart defects that weren't picked up on u/s-- AND most of them were born in hospitals and had newborn exams and still the defect (or murmur) wasn't picked up. It wasn't until they went home and "fell apart" and were brought to an ER that the defect was found.
For me, the reason I chose to have the anatomy scan done, is not because I think it is fool proof, but because there are several anomalies that exist that are treatable and the difference between life and death is heavily dependent on where the child is born. I choose to do it, knowing that it might not catch something (even something major) and knowing that it could cause unneccessary worry (or false reassurance)-- because, in the end, I want to feel like I've done my "due diligence."
But I
totally understand why other people make other choices.
So we did a quick scan and determined that she was head-down, and that she was in fact still a girl. 
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