I believe that it is worth investing in maternity jeans early on in your pregnancy - they are so much more comfortable on your expanding waist, even with a small bump so why wait? Also compared to normal jeans they will have limited wear (although I have friends who still wear theirs for a Sunday roast). You will most probably be wearing them for a while once the baby has arrived too - so get some you love.
If you've ever been pregnant, you know that maternity jeans can be a real saviour for your wardrobe. As your waistline expands, everything starts to not fit quite so well (sob!), and it can get uncomfortable—not to mention expensive. But if you have some decent denim options at your disposal, you can at least wear some of your looser tops over your bump. And there are some brilliant jeans that can help with that.