That's the dumbest thing I've read all morning!
To estimate blood volume of a new born baby the following calculation is used:
EBV= weight (kg) * Average blood volume
Average blood volume for a full term neonate is 85 mL/kg
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A typical adult has a blood volume of approximately between 4.7 and 5 litres, with females generally having less blood volume than males.
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(Info for anyone not math challenged.)
Oh, BTW...
The blood of a baby and it's mother NEVER mixes; it is a totally different type.