The use of during pregnancy is most associated with premature birth, low birth-weight infants, and fetal death.

The use of smoking during pregnancy is most associated with premature births ,low birthweight infants ,and fetal death

Well.. This could be smoking or alcohol. Because alcohol can cause the fetus to not develop correctly for example. The brain is something that can be not developed the right way and when the baby's brain has to start growing to keep up with the rest of the body it cannot grow due to complications with alcohol and/or drugs. And smoking cause low birth- weights for infants. So in this case i would just put drugs. Since alcohol is best considered as a drug and as well as smoking. 

The use of _drugs_ during pregnancy is most associated with premature birth, low birth-weight infants, and fetal death. 

Good Luck! :)