Using alcohol and illegal drugs during pregnancy threatens the health of your unborn baby. So does using legal drugs in an inappropriate way. When you use alcohol or drugs, the chemicals you ingest or breathe into your lungs cross the placenta and enter your baby. This puts your baby at risk for such problems as stillbirth, low birth weight, birth defects, behavioral problems, and developmental delays. 

Alcohol 
When you drink alcohol, so does your baby. Pregnant women should not drink alcohol to eliminate the chance of giving birth to a baby with fetal alcohol spectrum disorder (FASD). FASD involves a range of harmful effects that can occur when a fetus is exposed to alcohol. The effects can be mild to severe. Children born with a severe form of FASD can have abnormal facial features, severe learning disabilities, behavioral problems, and other problems. 
You might think a drink now and then won't hurt your baby. But we don't know how much alcohol it takes to cause harm. We do know that the risk of FASD, and the likely severity, goes up with the amount of alcohol consumed during pregnancy. Also, damage from alcohol can occur in the earliest stages of pregnancy — often before a woman knows she is pregnant. For this reason, women who may become pregnant also should not drink. 

Illegal drugs 
Many women who use illegal drugs also use tobacco and alcohol. So, it's not always easy to tell the effects of one drug from that of alcohol, tobacco, or other drugs. We do know that using illegal drugs during pregnancy is very dangerous. Babies born to women who use drugs such as cocaine, heroine, and methamphetamine are likely to be born addicted and must go through withdrawal. Mothers who inject drugs are at higher risk of getting HIV, which can be passed to an unborn baby. Some studies suggest that the effects of drug use during pregnancy might not be seen until later in childhood.
 
Getting help for alcohol or drug use 
If you drink alcohol or use drugs and cannot quit, talk to your doctor right away. Treatment programs can help pregnant women with addiction and abuse. To find help near you, go to the Substance abuse treatment facility locator. You can quit using and give your baby a good start to life.