you will have make your own judgement. planning to get pregnant may not mean that the baby will be born before/on December 31, 2012. If a baby will be born next year, then I would put at least the deductible amount (maybe closer to the out of pocket limit).
You might also would like to ask them if you are able to change the FSA amount in the middle of the year because the birth of a baby qualifies as " big life change event".