Many soft drinks have 20 to 40 milligrams of caffeine per serving. So as long as you limit your consumption, your fertility shouldn’t be affected.
But experts say that even more than the caffeine in soft drinks, it’s the sugar that may be the biggest potential problem. Sweet soft drinks can negatively affect blood sugar and insulin levels, a concern especially for women with PCOS, a common fertility-spoiler. So if you can’t give up your soda habit, at least switch to sugar-free for now (ask your doctor if artificial sweeteners are safe during pregnancy).
For more fertility tips, check out Conceive's book, Fertility Facts: Hundreds of Tips for Getting Pregnant.