Effects of Marijuana Use During Pregnancy

Effects of Marijuana Use During Pregnancy

Effects of Marijuana Use During Pregnancy

Effects of Marijuana Use During PregnancyDuring pregnancy, women who smoke marijuana expose their developing fetuses to the drug when it passes to the fetal bloodstream inside the placenta. There is considerable disagreement among medical professionals about the impact of marijuana on fetal development, in part because women who use the drug also commonly use other substances that can alter the development process. Still, current evidence indicates that use of marijuana during pregnancy can potentially produce negative effects on the viability of that pregnancy, as well as negative effects on the long-term learning capabilities of children exposed to the drug in the womb.

The Basics

An expectant mother’s bloodstream does not connect directly to the bloodstream of her developing fetus. Instead, both of these bloodstreams flow through opposite sides of the placental barrier, a grouping of tiny blood vessels inside the placenta. Oxygen, nutrients, and a variety of other substances pass from the mother’s blood through the placental barrier, and then into the fetal bloodstream. At the same time, carbon dioxide and other waste products pass from the fetus’s blood through the placental barrier, and then into the maternal bloodstream. When an expectant mother uses marijuana, the drug’s active ingredient (called tetrahydrocannabinol or THC) passes through the placental barrier along with various other materials, and thereby enters the fetal circulation.

Potential for Pregnancy Complications and Premature Birth

Just like cigarette smoking, marijuana smoking elevates the amount of carbon dioxide and carbon monoxide circulating in a pregnant woman’s bloodstream. Elevations in these substances lead to a reduction in the blood’s oxygen content; in practical terms, this means that there will be less oxygen available to pass through the placental barrier and enter the system of a developing fetus. One potential consequence of this oxygen depletion is an increased risk for a miscarriage in the first 20 weeks of pregnancy. According to a study published in 2012 in the Journal of Biological Chemistry, marijuana use can also potentially trigger changes inside the placenta that contribute to the onset of preeclampsia, a dangerous pregnancy complication involving high blood pressure (hypertension) and the abnormal presence of protein in an expectant mother’s urine.

Marijuana use may also increase a woman’s risks for premature labor and birth of a child before a pregnancy reaches its 37th week. Children born prematurely have heightened risks for a variety of serious problems, including vision difficulties, hearing difficulties, jaundice, bleeding in the brain, unusual susceptibility to infection, cerebral palsy, decreased or delayed development of mental function, and a form of interrupted breathing called apnea.

Potential for Low Birth Weight

Along with the potential for premature birth, children born to marijuana-smoking mothers may have increased risks for being born at a weight of less than five pounds, eight ounces. By standard medical definition, doctors consider children born below this limit to have an unusually low birth weight, whether or not they are born prematurely. When viewed from a long-term perspective, children born below the low birth weight threshold have increased risks of developing heart disease, hypertension, and type 2 diabetes, a condition characterized by the onset of blood glucose control problems in later life.

Potential for Learning Impairment

Children born to marijuana-smoking mothers apparently have increased risks for developing learning problems, the American Pregnancy Association reports. Specific problems that may occur include delayed development of age-appropriate skills and a disruption of executive function, a term doctors use to describe the exercise of diverse mental abilities such as problem solving, planning, maintaining concentration, effectively using memory, switching between tasks, controlling impulsive behavior, engaging in verbal reasoning, and monitoring one’s actions over time. Impairments in executive function may manifest in ways that are relatively subtle.


As indicated previously, pregnant women who use marijuana also frequently use other substances—such as tobacco and alcohol—that are capable of producing damaging changes in fetal development or the overall course of a pregnancy. For this reason, doctors and researchers have considerable difficulty isolating the pregnancy-related effects of marijuana from the effects of other harmful influences. In addition, even when it does cause problems, marijuana use apparently does not cause them as consistently as, for example, heavy alcohol consumption would. Because of these considerations, pregnant women may sometimes view marijuana use as a relatively “harmless” endeavor. However, from a medical standpoint, it’s unwise to dismiss the potential impact of the drug, especially when it’s used in combination with other harmful substances.

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