What does this mean?? I’m confused

Question

Had my 20 week ultrasound & I’m confused as to why there’s so many different weeks .. such as 21-23 weeks .. can someone explain all this please.?
It says ultrasound is 21 weeks & 1 day but LMP has me as 20 weeks & 3 days.. Someone explain what everything mean please

Answer

Baby might be measuring 21 weeks at your appointment. Normal

Answer

Your basically with in a one week sizing dating based on scans which is pretty typical. Become babies in womb comes in all sizes so nothing off there. 
The rest is just basic measurements of the baby and womb which are pretty typical an normal to be taken at this time. I don’t see anything personally that seems off or wrong . It’s all pretty basic which is good!

What does this mean?? I’m confused

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