How in the world do women gain up to 60 pounds from a baby who weights 5-10 pounds?

I can understand 15=30.

but 60?
-.-

Metabolism changes from the hormones. Or perhaps they eat more. I know one woman with twins who gained 50 pounds in 2 months.

Pregnant women do not just gain "baby" weight. For starters, the body makes lots of changes preparing for a healthy pregnancy and delivery. To help, women have to change their diets to support the change. Also, the breasts swell to be able to feed them after birth. The uterus grows with the baby... eh, I don't feel like typing it all out. Just check out this link ;)
Where the weight comes from (http://www.americanpregnancy.org/pregnancyhealth/eatingfortwo.html)