Here's a curiosity: the measurement in centimetres that the midwife takes of the uterus matches the number of weeks' gestation. PP is 36cm right now, ie 36 weeks.
Putting aside the obvious difficulties (how did it work before metrication? if a non-pregnant woman has a 10 cm uterus is she permanently 10 weeks pregnant?), there's a satisfying cubic function at work here. Assuming the measurement is a chord on a sphere, and if we know the radius (tummy-button to spine) and the angle (around 90 degrees), it is possible to work out the weight gain between now (36cm) and 40 weeks (ie, 40cm) if her density is about 0.9 (when compared with water).
With me so far? Good.
Since my density is waaaaay above 1.0, I'm not about to attempt to work this out. The summary is: she is going to grow much, and I mean *MUCH*, bigger.
It's all to do with linear vs volumetric. As a quick glance through On being the right size by J B S Haldane will tell you, a 36 to 40 linear increase is slightly less than 10%; the same figures give a volume increase of about 23% .
And she thinks she is big now!
"On being the right size," found at http://irl.cs.ucla.edu/papers/right-size.html
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