Drug use early during pregnancy can affect the developing organs and limbs of the fetus. Even one episode of drug use during this period can affect the development of your child. Often the result is a birth defect or miscarriage.Drug use later in pregnancy can affect development of your baby's central nervous system.rug use early during pregnancy can affect the developing organs and limbs of the fetus. Even one episode of drug use during this period can affect the development of your child. Often the result is a birth defect or miscarriage.