Do you have to be pregnant in order for the vitamins to work? I took them religiously when I was pregnant but stopped when I stopped nursing. I had heard once you're not pregnant anymore they wouldn't be good.
What do you mean by would they work? What they are is a collection of vitamins and minerals specially formulated to fulfill the pregnant body's needs. They're more expensive than normal multivitamins, which are enough to support you when you're not pregnant or nursing, but they should certainly have enough of everything you need then too.
Two things to check for, though, before continuing to use prenatals when not pregnant, nursing, or ttc, are Vitamin A content and Iron content. Both of these are things you need more of when getting ready for or sustaining a baby, but things which in excess can be dangerous. Make sure your vitamin doesn't have substantially more than the RDV of either one and you'll be fine.
Mine say for pregnant and breastfeeding women. When we were in college lots of girls took them to make thier hair and nails pretty (I stopped because they made me constipated) Anything your body doesn't use just goes into the toilet anyway.