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.
During my first trimester, I thought I might get away with continuing to wear my low-slung hipster jeans for the duration. And I probably could have eeked them out for way longer than I did, had I invested in button extenders or a Bump Bandeau (as recommended by JTryner in an earlier thread). But there was always going to come a point when I got a little larger all over (be it from swelling, fat or, y'know, the extra 2 ½ pints of blood that swishes around in women when they're growing a foetus).
Today, Old Navy is one of the largest clothing companies around the globe, and its maternity clothes are a perfect extension of the styles and ideas this trendy brand has long embraced. Old Navy for Maternity proudly sets itself apart from other maternity clothes companies in a few key ways. While Gap – Maternity and Motherhood offer classic clothes at premium price points, Old Navy for Maternity champions current fashions at affordable prices. With casual, professional, and special occasion options, Old Navy has all of your maternity clothes needs covered.