What is considered day 3?!?!

Question

Okay ladies, I need help! 
I am new to my fertility journey and honestly...Its alot!! 
I had my first consult and my doctor ordered day 3 bloodwork. But my question is....how do you calculate day 3? This may seem like an easy answer but like...I just primarily started tonight at 7pm......is this day 1? Or is day 1 tomorrow where I have full bleeding all day?
Any help or support would be greatly appreciated.

Answer

My clinic calculte day one if the period started before 3pm, otherwise after 3 pm day one is the day after

Answer

I’d count today as day 1. If you go between say 3-5 it is all about the same so I wouldn’t go crazy over calculating it.

Answer

My Fertility clinic says if you start your period after 5 pm, the next day (aka the first full day of full flow) is CD1

What is considered day 3?!?!

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