Caffeine is a stimulant and can be found in many beverages and foods: coffee, tea, chocolate, soft drinks, and some medications. When you eat or drink things that contain caffeine, this drug passes into your bloodstream, then through the placenta to your baby. Studies on animals have found that high levels of caffeine can cause birth defects, and there is further evidence that too much caffeine causes low birth weight in babies. To be safe, limit your intake of caffeine.