If you build a house on empty land it's called an improvement.

A woman's belly becomes the baby's house for the nine months of her pregnancy. By knocking her up, you're building up the empty real estate that is her belly. That's what I really mean when I call a pregnant woman's belly an "improvement", lol. And just like built up real estate, she's worth much more by my valuation. 

So what affects my valuation of a pregnancy?

Well, there's:

1) Size - obviously, the bigger the better. So in a way this is directly related to how far along she is, but can also be affected by genetics and the health of her and her baby. But in general, the bigger her belly, the higher my valuation;

2) Shape - this is a trickier metric as this can be more subjective than just size, and this also takes into account not just the shape of the belly itself, but the mother's body as well. Like how a well-maintained house is more expensive than an ill-maintained one, a fitter preggo body scores higher.

3) Maternal instincts - this might be more subjective, but little things like her caressing her belly regularly, her attitude towards her pregnancy and the like, also affects my valuation. Self-destructive things like smoking and drinking alcohol while pregnant are negatives.

Oh heavens, look at the time. Time to do some more valuations.