There are two different ways for non-profits to word their mission statements.  The best way would be in terms of  vision and results, rather than as a  general purpose.

Here is an example of a general purpose type of mission statement:

"We exist to offer compassionate Christ-centered care and support to women facing unplanned pregnancies, including pregnancy tests, counseling, and material support." 

The challenge with a statement like this is that there are very few ways to know if you're achieving it.
Are services being presented in a Christ-centered way?
Are you offering tests, counseling, and material support?

These are about the only questions you could ask.

What tells if you are going anywhere?  Is there a destination?  Is anything being achieved?  Is there indeed a movement in the right direction?

By contrast, a results-oriented, visionary-type mission statement might be:

"To empower as many individuals as possible in the greater Jefferson County area to make healthy life choices related to their sexuality and child-bearing, consistent with the sanctity of human life."

Realize a mission statement such as this is truly visionary and aims for the ideal (as it should), and thus will probably never be fully achieved.

However, the high ideals reflected in this statement give a standard by which to judge if your center is making a difference and always moving ahead.  It also gives a standard by which to evaluate potential new programs worth considering for the future.