Beer and wine are just as bad for the baby as hard liquor. Some studies suggest that women who drink before pregnancy tend to have smaller babies. Persistent and significant drinking during pregnancy can cause fetal alcohol syndrome, as a result of which infants may be born with brain, heart, and nervous system problems, distinctive facial abnormalities, and mental retardation. Smoking increases your chances of a miscarriage during the first trimester. Prospective fathers who smoke should also quit, as exposure to passive smoking during pregnancy is also harmful.
Smoking also impairs a woman's fertility.
Smoking affects sperm and may impair male fertility too. Pregnant women should limit themselves to the equivalent of one cup of coffee daily. Caffeine may increase the risk of late first or second trimester miscarriage. So start weaning much before conception. Illegal drugs are bad for your health, whether or not you are pregnant and they can only harm a baby.