You don't really, since I have seen their finances personally. You are assuming you know, but in reality, you don't.
$5,000 insurance deduct, 80/20 up to 10,000, average vag birth and prenatal care costs $7500. That means that they will be paying $5,500 out of pocket alone. With your math, that takes their monthly income down to $1416 per month. You came up with $1475 in expenses per month.
Now tell me, how is -59 per month with your math "not a huge struggle"?