Use of Marijuana During Pregnancy Omaha NE

Use of Marijuana During Pregnancy

By Lynn Zimmer and John P. Morgan

Warnings that marijuana causes birth defects date back to the late 1960s.1 Some researchers claimed to have found chromosomal abnormalities in blood cells taken from marijuana users. They predicted that young men and women who used marijuana would produce deformed babies.2 Although later studies disproved this theory,3 some current drug education materials still claim that genetic damage is passed on by marijuana users to their children.4

Today, researchers look for a direct effect of THC [for tetrahydrocannabinol, either of two physiologically active isomers, C21H30O2, from hemp plant resin] on the fetus. In animal studies, THC has been shown to produce spontaneous abortion, low birth weight, and physical deformities—but only with extremely large doses, only in some species of rodents, and only when THC is given at specific times during pregnancy.5 Because the effects of drugs on fetal development differ substantially across species,6 these studies have little or no relevance to humans. Studies with primates show little evidence of fetal harm from THC.7 In one study, researchers exposed chimpanzees to high doses of THC for up to 152 days and found no change in the sexual behavior, fertility, or health of their offspring.8

Dozens of studies have compared the newborn babies of women who used marijuana during pregnancy with the babies of women who did not. Mainly, they have looked for differences in birth weight, birth length, head circumference, chest circumference, gestational age, neurological development, and physical abnormalities. Most of these studies, including the largest study to date with a sample of over twelve thousand women,9 have found no differences between babies exposed to marijuana prenatally and babies not exposed.10 Given the large number of studies and the large number of measures, some differences are likely to occur by chance. Indeed, researchers have found differences in both directions. In some studies, the babies of marijuana users appear healthier and hardier.11 In others, researchers have found more adverse outcomes in the babies of marijuana users.12

When adverse outcomes are found, they are inconsistent from one study to another, always relatively minor, and appear to have no impact on infant health or mortality.13 For example, in one recent study, researchers reported a statistically significant effect of marijuana on birth length. The marijuana-exposed babies, on average, were less than two-tenths of one inch shorter than babies not exposed to marijuana.14 Another study found a negative effect of marijuana on birth weight, but only for White women in the sample.15 In a third study, marijuana exposure had no effect on birth weight, but a small negative effect on gestational age.16 Overall, this research indicates no adverse effect of prenatal marijuana exposure on the physical health of newborns.

Researchers have also examined older children for the effects of prenata...

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