Smoking pot while pregnant — will it harm the baby later on?

Originally Published: September 6, 2002 - Last Updated / Reviewed On: August 3, 2015
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Dear Alice,

What happens if you smoke weed while you are pregnant? Will the baby have problems in the future?

Dear Reader,

Research studies have shown that women who use recreational drugs during pregnancy tend to use marijuana, thinking that it won't harm the fetus as much as other illegal substances. Although no clear-cut deformity or syndrome is known to occur due to marijuana use during pregnancy (as there is from alcohol use, for example, with fetal alcohol syndrome), there are possible dangers.

First of all, smoking anything during pregnancy deprives the fetus of oxygen. Just as smoking tobacco is discouraged in pregnant women, so is smoking marijuana. Smoking any type of substance interferes with the fetus's blood supply. This can mean the fetus doesn't get enough oxygen, and s/he may be born smaller in both weight and length. Smaller babies have a higher risk of other problems after birth, such as infections, severe jaundice, difficulty feeding, breathing problems, low blood sugar, difficulty regulating temperature, bleeding into the brain, and problems with vision.

Secondly, it's possible that marijuana can be "laced" with other substances. So the fetus may be unintentionally exposed to other potentially harmful substances in addition to marijuana.

Marijuana can also be transmitted through breast milk.  Tetrahydrocannabinol, or THC (the main active ingredient in marijuana), can be as much as 8 times higher in breast milk than in the mother's bloodstream.  Babies whose mothers have used marijuana during pregnancy or while breastfeeding sometimes seem jittery and difficult to comfort. They may have some delay in the development of their motor skills, although studies have concluded that this delay may not be permanent.  In any case, it is advisable not to smoke marijuana while breastfeeding.

Since we're on the subject of substance use during pregnancy and breastfeeding, if you already drink alcohol or smoke cigarettes, it's in your baby's (and your) best health interests to stop when you are pregnant. During the nursing period, it's commonly recommended that mothers drink only modest amounts of alcohol, delay breastfeeding for 2 - 3 hours after drinking alcohol, and avoid exposing the baby to second-hand smoke.

It should be noted that much of the research on the effects of prenatal exposure to marijuana has been complicated and inconclusive.  This is mainly because it is difficult to isolate the effects of marijuana from other possible factors such as alcohol, other drug use, socioeconomic status, family structure, and mother's personality.  All in all, the healthiest choice for you and your baby is to avoid using recreational chemicals, including marijuana, while pregnant. As difficult as it may be to change one's lifestyle, taking a break from smoking cigarettes and joints, and drinking alcohol and using other drugs, can help set your baby up for a long, healthy life.

For more information, contact the March of Dimes.

Alice