Make sure you take your leave as INTERMITTENT. This will allow you to not only take time for your wifes pregnancy, the birth of the child, but also allow you to assist your wife in the caring for the child such as doctor appointments,etc. You are allowed to take it in any increments, weeks,days, hours,etc as you need. It also allows you to work your contracted hours (say 8 for a ft driver) and then leave to take care of your needs and it does not count against your available FMLA time.
You get 12 weeks unpaid but UPS will substitute paid time for unpaid FMLA time until you have exhausted any paid time. You are allow to save one week of vacation time separate from any FMLA time if you choose to, it is marked off on the FMLA form. As pointed out above any state FMLA laws affording you greater benefits will prevail over the federal laws.