Very interesting thread. I have an aunty who is addicted to coke. She has osteoporosis and kidney stones which are due to drinking nothing but coke. Coke actually leaches the calcium out of your bones, so probably something to keep in the back of your mind, make sure you keep your calcium boosted for you and your little ones.
Now THAT makes some sense. Smokers placentas usually look alder than those of non-smokers, and have more calcium deposits. I had an "oldish" placenta, "a bit gritty" my MW said. DD was born at 41+4, so possibly that was why. I didn't drink coke or smoke. If coke leaches calcium from your bones it presumably is excreted by the liver, but if you were PG it's possible it could build up in the placenta instead?

Feeb, does TAR get into placenta's of smoking women?! I cannot imagine the mechanism for that - tar doesn't get into your blood, it sticks in your lungs, gums them up, makes you cough and eventually gives you cancer...

Bx