surprise

sur·prise [ser-prahyz, suh-]verb, sur·prised, sur·pris·ing, noun 

verb (used with object)

1. to strike or occur to with a sudden feeling of wonder or astonishment, as through unexpectedness: Her beauty surprised me.

2. to come upon or discover suddenly and unexpectedly: We surprised the children raiding the cookie jar.

3. to make an unexpected assault on (an unprepared army, fort, person, etc.).

4. to elicit or bring out suddenly and without warning: to surprise the facts from the witness.

5. to lead or bring unawares, as into doing something not intended: to surprise a witness into telling the truth.

noun

6. an act or instance of surprising or being surprised.

7. something that surprises someone; a completely unexpected occurrence, appearance, or statement: His announcement was a surprise to all.

8. an assault, as on an army or a fort, made without warning.

9. a coming upon unexpectedly; detecting in the act; taking unawares.

As in,

Surprise! I'm pregnant.

Specifically used with definitions #5 and #7.