What are the bad long term side effects of caffeine consumption on the fetus?

Unclear. No long-term studies have addressed this; minimal-to-moderate caffeine consumption appears to be safe as far as perinatal/pregnancy outcomes are concerned. One cannot be certain what (if any) effects maternal caffeine consumption has on the developing fetal brain or cardiovascular system, however excessive intake can cause fetal arrhythmias (irregular heartbeat) and jittery neonatal reflexes.