In every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk. This sheet talks about whether exposure to marijuana may increase the risk for birth defects over that background risk. This information should not take the place of medical care and advice from your health care provider.

What is marijuana?

Marijuana, also called pot, weed, or cannabis, is a drug that comes from the hemp plant. Parts of the plant are dried and smoked in pipes or cigarettes (joints) or sometimes eaten. It is an illegal substance in parts of the United States; however, some states allow marijuana use by prescription for medical purposes, and some states allow the sale of marijuana for recreational use.

The main active chemical in marijuana is delta-9-tetrahydrocannabinol (THC). Another component of marijuana is cannabidiol (CBD). Both THC and CBD are known to cross the placenta during pregnancy and reach the baby’s system.

How much is known about the effects of marijuana on a pregnancy?

It is difficult to accurately study marijuana use during pregnancy. Marijuana contains about 400 different chemicals, and some marijuana cigarettes may contain contaminants, such as other drugs, pesticides, or fungi. Some women who use marijuana may also use alcohol, tobacco, or other drugs at the same time. Women who use marijuana during pregnancy may also have other factors that can increase pregnancy complications, such as lack of prenatal care or an unbalanced diet. In addition, marijuana has become more potent (stronger), particularly in THC content over the past years. Many growers are focusing on sinsemilla. Sinsemilla refers to growing marijuana a certain way to get a more potent (stronger) marijuana product. Therefore, studies done years ago would, in theory, be looking at marijuana that was less strong than currently being used. Finally, information on the amount, frequency, and timing of marijuana use can be difficult to accurately collect. All of these factors explain why studies looking at marijuana use during pregnancy sometimes find different results.

I am trying to become pregnant. If I or my partner uses marijuana, do I have a lower chance of becoming pregnant?

In women, long-term use of marijuana may affect the menstrual cycle and lead to a reduction in hormones involved in reproduction and fertility. In men, an association with reduced sperm count has been seen. These side effects might make it harder to get pregnant. The effects on fertility appear to go away when marijuana use is stopped.

Will smoking or eating marijuana cause birth defects in my baby?

Most studies have not found an increase in the chance for birth defects among babies prenatally exposed to “occasional” marijuana use. A few studies have suggested a small increase in the chance for gastroschisis (a rare birth defect in which the infants’ intestines stick out of an opening in the abdominal wall), and one study reported an increased chance for heart defects among babies prenatally exposed to marijuana. It can be difficult to draw conclusions from these studies because most of the women who used marijuana also used other substances at the same time or had other factors that may have increased their chance for these defects. Also, the term “occasional” use is hard to quantify and might be different from person to person.

While most studies are reassuring regarding birth defects, without good studies among heavy marijuana users, and because of other potential pregnancy complications it is best to avoid marijuana during pregnancy.

Can marijuana harm the baby in any other way?

Some studies have suggested that among women who smoke marijuana cigarettes regularly, there is an increased chance for pregnancy complications such as: premature birth, low birth weight, stillbirth and small length, small head size, and death in the newborn period. Babies that are born prematurely or with low birth weight can have higher rates of learning problems or other disabilities.

Similar to what is seen with cigarette smoking, smoking marijuana may increase carbon monoxide levels in the blood, which can decrease the amount of oxygen the baby receives, and this can also affect the growth of the baby. Some studies have suggested that lower birth weight is more likely to occur among women who also smoke cigarettes in addition to their marijuana.

If I smoke marijuana in the third trimester, can it cause my baby to go through withdrawal after birth?

Some newborns exposed to marijuana have been reported to have temporary withdrawal-like symptoms, such as increased tremors and crying. These symptoms usually go away within a few days.

Can my marijuana smoking affect the brain development of the baby?

Differences in brain activity, behavior, and sleeping patterns of infants and children exposed to marijuana in pregnancy have been reported in some studies. It is believed that these children might have more problems with attention, impulsive behavior, short term memory, academic performance and difficulty at work as an adult. These problems have been seen more often in children whose mothers were “heavy” marijuana users (smoked one or more marijuana cigarettes per day). The evidence is not conclusive and some studies report conflicting results.

What happens if I use marijuana when I’m breastfeeding?

Marijuana can be passed to infants through their mother’s breast milk. Marijuana may also affect the quality and quantity of breast milk that you make. There are no good studies on how marijuana in breast milk might affect a nursing baby. Although no consistent effects have been noticed in infants exposed to marijuana through breast milk, the American Academy of Pediatrics and the Academy of Breastfeeding Medicine advise that breastfeeding mothers avoid using marijuana. Be sure to talk to your health care provider about all your breastfeeding questions.

References Available By Request