Does smoking b4 you were pregnant affect your baby & have a chance of miscarrying ?

No it will not: If you do not smoke when you get pregnant, there will be no effect on the fetus or the delivery.

Differentiate before: You conceived all of the metabolites of tobacco were out of your body vs. You stopped smoking when you found out you were pregnant & if you were still exposed to others' tobacco smoke at home or at work. Decreased gray matter & altered development of white matter of the fetal brain may cause deficits in iq, speech & language, visual/spatial abilities & behavior even with passive smoking.