If you were measuring ahead, did you go into labor "early"?

Betty
Those of you that consistently measured ahead throughout your pregnancy, did you go into labor before your due date? I realize they say you go by your first scan because it's very accurate, but for example, if that's the case, why do some people not see the baby yet at 6 week and others do? 
My mom always measured ahead with me and she had me "early." I don't think it was really early, I think that she was further along. I've heard other similar stories. I am having my anatomy scan and first ultrasound since I was 6 weeks (currently 20) this Monday and I've always tracked very well. According to my calculations, I'm a couple weeks further along. I get how ovulation works and that sperm can live for quite a few days, but 2-3 weeks seems like a long time to be off by. 
I haven't been seeing a doctor so I haven't had any other measurements or ultrasounds done. I just went to a clinic when I first found out to make sure baby was alive and hadn't had care until now because I have a midwife and she doesn't start prenatal care until 16 weeks.  So this is barely my second appt coming up. I'm curious as to whether I will measure ahead, which I'm expecting. 
So the questions again: If you measured ahead during your pregnancy, did you go into labor early/before your due date? 

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