When I got my first pig I thought she was pregnant because her belly grew so fast... but turns out she was just a chubber
~love ya Crystal~
Is Dart's belly feeling soft or firm? Seems like a firm belly could be a sign. (Crystal's belly was soft and a co-worker of mine's pregnant female's belly was noticeably firm)
That's about all I can contribute... sorry.
Erin seems to have quite a bit of experience in that department... maybe she'll be along and can be of more help!
Other than that... 10 weeks from the first day you had her in with your male and you'll know for sure

Males can impregnant females as early as about 3-4 weeks of age!
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~Chalupa, Lady, Moxie, Paiseley & Boozer~