Can there be an effect if you had four sips of Senna tea and questiong if your pregnant or not? Can those four sips harm the baby or you need to drink a full class to have a result of some kind of damage?
Comment - you should consult your doctor - no amount of senna tea is safe if pregnant.
I am not a herbalist or doctor so I can not comment further. Please advise your doctor. Sounds like a small amount but better to be safe.