USE OF MARIJUANA DURING PREGNANCY

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 prenatal
exposure to marijuana. A study of one-year-olds found no differences
between marijuana-exposed and nonexposed babies on measures of health,
temperament, personality, sleeping patterns, eating habits, psychomotor
ability, physical development, or mental functioning.17 In two studies, one
of three-year-olds,18 the other of four-year-olds,19 there was no effect of
prenatal marijuana exposure on children's overall IQ test scores. However,
in the first study, when researches looked at Black and White children
separately, they found, among Black children only, slightly lower scores on
two subscales of the IQ test. On one subscale, it was children exposed to
marijuana only during the first trimester who scored lower. On the other
subscale, it was children exposed during the second trimester who scored
lower.20 In neither case did the frequency or quantity of mothers'
marijuana use affect the outcomes. This makes it highly unlikely they were
actually caused by marijuana. Nonetheless, this study is now cited as
evidence that using marijuana during pregnancy impairs the intellectual
capacity of children.21

Also widely cited are two recent case-control studies describing a
relationship between marijuana use by pregnant women and two rare forms of
cancer in their children. A case-control study compares people with a
specific disease (the case sample) to people without the disease (the
control sample). Using this method, researchers identify group differences
in background, environment, lifestyle, drug use, diet, and the like that
are possible causes of the disease.

A study of children with non-lymphoblastic leukemia reported a tenfold
greater risk related to their mothers' use of marijuana during pregnancy.22
A second study reported a threefold greater risk of rhabdomyosarcoma.23
These calculations were based on women's reports that they used marijuana
at some point during pregnancy. In the first study, ten out of the 204
case-group mothers (5 percent) reported marijuana use, compared to one out
of the 204 control-group mothers (0.5 percent). In the second study, 8
percent of case-group mothers reported using marijuana, compared to 4.3
percent of controls.

These studies do not prove that marijuana use by pregnant women causes
cancer in their children. They report a statistical association based
solely on women's self-reports of marijuana use. It is likely that both
groups of mothers underreported marijuana use; in other studies,
researchers have found that marijuana use by pregnant women typically
ranges from 10 to 30 percent.24 There is reason to suspect greater
underreporting by control-group mothers, who were randomly selected and
questioned about their marijuana use on the telephone. Because the mothers
of the sick children were trying to help researches identify the cause of
their children's disease, they had more reason to be honest about their
illegal drug use.

Like all case-control studies, these two studies identified many
differences between case-group mothers and control-group mothers, all of
which could possibly lead scientists to discover the cause of these rare
forms of cancer. Other factors associated with childhood rhabdomyosarcoma
include low socioeconomic status, fathers' cigarette smoking, a family
history of allergies, children's exposure to environmental chemicals,
childhood diets that include organ meats, mothers' use of antibiotics
during pregnancy, mothers being over age thirty at the time of the child's
birth, overdue delivery, and the child having had fewer immunizations.25
Without additional research, none of the factors that are statistically
associated with childhood cancer can be identified as causes of childhood
cancer. At this time, there is no corroborative evidence to link marijuana
with cancer. In fact, in a recent study, researchers found significantly
lower rates of cancer in rats and mice following two years of exposure to
extremely large doses of THC.26

Since 1978, psychologist Peter Fried and his colleagues have collected
longitudinal data on prenatal marijuana exposure as part of the Ottawa
Prenatal Prospective Study (OPPS). Over the years, these researchers have
administered hundreds of tests to the same group of children, assessing
their physical development, psychomotor ability, emotional and
psychological adjustment, cognitive functioning, intellectual capacity, and
behavior.

Out of all the OPPS studies and all the tests given, researchers have found
very few differences between marijuana-exposed and nonexposed children. At
age one, researchers found that marijuana-exposed infants scored higher on
one set of cognitive tests.27 At age three, the children of moderate
marijuana users (one to five joints per week during pregnancy) had higher
scores on one test of psychomotor ability.28 At age four, the children of
women who smoked marijuana heavily during pregnancy (an average of nineteen
joints per week) scored lower on one subscale of one cognitive test.29
However, at ages five and six, this difference was no longer present.30
When the children were six, the researchers added several new measures of
"attentional behavior." The children of heavy marijuana users scored lower
on one computer-based test of "vigilance."31 Eleven new psychological and
cognitive tests, administered to six-to nine-year-olds, showed no
statistically significant differences between the children of marijuana
users and nonusers. Parents rated marijuana-exposed children as having more
"conduct problems," but this difference disappeared after the researchers
controlled for confounding variables.32

Despite the overwhelming similarities in the children of marijuana users
and nonusers, in their published reports OPPS researchers consistently
highlight the occasional negative finding. Fried believes that these
findings underestimate the harms of prenatal marijuana exposure. He
suggests that "more sensitive measures" are needed because:

instruments that provide a general description of cognitive abilities may
not be capable of identifying nuances in neuro-behaviour that may
discriminate between the marijuana-exposed and non-marijuana exposed
children. . . . Tests that examine specific characteristics that may
underline cognitive performance may be more appropriate and successful.33

Recently, Fried predicted that a new test of "executive function" would
reveal marijuana-related deficits in preteen youngsters.34 A short time
later, Fried announced that preliminary analysis of his data showed this
effect was present.35 Almost immediately, his announcement appeared in U.S.
government reports as evidence of marijuana's harm to the fetus.36
Additional reports of harm based on the OPPS sample, which now includes
fewer than thirty marijuana-exposed children, may be forthcoming-despite
the fact that, according to Fried, the consequences of prenatal drug
exposure typically diminish as children get older.37 After controlling for
known confounding variables, Fried estimates that prenatal drug exposure
accounts for 8 percent or less of the variance in children's scores on
developmental and cognitive tests-and this estimate is for alcohol,
tobacco, and marijuana combined.38 In essentially all studies, marijuana
contributes less than alcohol or tobacco.39 In addition, the findings
differ from one study to another, and show no consistent relationship of
fetal harm to either the timing or degree of marijuana exposure. While it
is sensible to advise women to abstain from all drugs during pregnancy, the
weight of current scientific evidence suggests that marijuana does not
directly harm the human fetus.

NOTES 1. F. Hecht et al., "Lysergic-Acid-Diethylamide and Cannabis as
Possible Teratogens in Man," Lancet 2 (1968): 1087. G. Carakushansky et
al., "Lysergide and Cannabis as Possible Teratogens in Man," Lancet 1
(1969): 150-151.

2. T. H. Maugh, "Marihuana: The Grass May No Longer Be Greener," Science
185 (1974): 683-685.

3. S. Matsuyama and L. Jarvik, "Effects of Marihuana on the Genetic and
Immune Systems," in R. C. Petersen (ed.), Marihuana Research Findings, 1976
(Rockville, MD: National Institute on Drug Abuse, 1977), 179-193. K.
Morishima, "Effects of Cannabis and Natural Cannabinoids on Chromosomes and
Ova," in M. C. Braude and J. L. Ludford (eds.), Marijuana Effects on the
Endocrine and Reproductive Systems (Rockville, MD: National Institute on
Drug Abuse, 1984), 25-45.

4. Parents Resource Institute for Drug Education, Marijuana: Effects on the
Male, (Atlanta, GA: PRIDE, 1996). W. R. Spence, Marijuana: Its Effects and
Hazards (Waco, TX: Health Edco, undated). Peggy Mann, The Sad Story of Mary
Wanna (New York: Woodmere Press, 1988), 30.

5. J. Herclerode, "The Effect of Marijuana on Reproduction and
Development," in R. C. Petersen (ed.), Marijuana Research Findings: 1980
(Rockville, MD: National Institute on Drug Abuse, 1980), 137-166. E. L.
Abel, "Effects of Prenatal Exposure to Cannabinoids," in T. M. Pinkert
(ed.), Current Research on the Consequences of Maternal Drug Abuse
(Rockville, MD: National Institute on Drug Abuse, 1985), 20-35. D.
Hutchings and D. Dow-Edwards, "Animal Models of Opiate, Cocaine, and
Cannabis Use," Clinics in Perinatology 18 (1991): 1-22. M. Behnke and F. D.
Eyler "The Consequences of Prenatal Substance Use for the Developing Fetus,
Newborn, and Young Child," International Journal of the Addictions 28
(1993): 1341-1391. T. Wenger et al., "Effects of
Delta-9-Tetrahydrocannabinol on Pregnancy, Puberty, and the Neuroendocrine
System," in L. Murphy and A. Bartke (eds.), Marijuana/Cannabinoids:
Neurobiology and Neurophysiology (Boca Raton, FL: CRC Press, 1992), 539-560.

6. A. M. Rudolph, "Animal Models for Study of Fetal Drug Exposure," in C.
N. Chiang and C. C. Lee (eds.), Prenatal Drug Exposure: Kinetics and
Dynamics (Rockville, MD: National Institute on Drug Abuse, 1985), 5-16

7. P. A. Fried, "Postnatal Consequences of Maternal Marijuana Use," in T.
M. Pinkert (ed.), Current Research on the Consequences of Maternal Drug
Abuse (Rockville, MD: National Institute on Drug Abuse, 1985), 61-72. M. S.
Golub et al., "Peer and Maternal Social Interaction Patterns in Offspring
of Rhesus Monkeys Treated Chronically with Delta-9-Tetrahydrocannabinol,"
in S. Agurell, The Cannabinoids: Chemical, Pharmacological, and Therapeutic
Aspects (Orlando, FL: Academic Press, 1984), 657-667. J. Herclerode (1980),
see Note 5.

8. D. M. Grilly et al., "Observations on the Reproductive Activity of
Chimpanzees Following Long-Term Exposure to Marijuana," Pharmacology 11
(1974): 304-307.

9. S. Linn et al., "The Association of Marijuana use with Outcome of
Pregnancy," American Journal of Public Health 73 (1983): 1161-1164.

10. P. H. Shiono et al., "The Impact of Cocaine and Marijuana Use on Low
Birth Weight and Preterm Birth: A Multicenter Study," American Journal of
Obstetrics and Gynecology 172 (1995): 19-27. E. M. Knight et al.,
"Relationships of Serum Illicit Drug Concentrations During Pregnancy to
Maternal Nutritional Status," Journal of Nutrition 124 (1994): 973-980S. K.
Tennes and C. Blackard, "Maternal Alcohol Consumption, Birthweight, and
Minor Physical Abnormalities," American Journal of Obstetrics and
Gynecology 138 (1980): 774-780. J. Hayes et al., "Newborn Outcomes with
Maternal Marijuana Use in Jamaican Women," Pediatric Nursing 14 (1988):
107-110. P. A. Fried and C. M. O'Connell, "A Comparison of the Effects of
Prenatal Exposure to Tobacco, Alcohol, Cannabis and Caffeine on Birth Size
and Subsequent Growth," Neurotoxicology and Teratology 9 (1987): 79-85. C.
M. O'Connell and P. A. Fried, "An Investigation of Prenatal Cannabis
Exposure and Minor Physical Anomalies in a Low Risk Population,"
Neurobehavioral Toxicology and Teratology 6 (1984): 345-350. G. A.
Richardson et al., "The Effect of Prenatal Alcohol, Marijuana and Tobacco
Exposure on Neonatal Behavior," Infant Behavioral Development 12 (1989):
199-209. S. Astley, "Analysis of Facial Shape in Children Gestationally
Exposed to Marijuana, Alcohol, and/or Cocaine," Pediatrics 89 (1992):
67-77. F. R. Witter and J. R. Niebyl, "Marijuana Use in Pregnancy and
Pregnancy Outcome," American Journal of Perinatology 7 (1990): 36-38.

11. M. C. Dreher et al., "Prenatal Exposure and Neonatal Outcomes in
Jamaica: An Ethnographic Study," Pediatrics 93 (1994): 254-60. K. Tennes et
al., "Marijuana: Prenatal and Postnatal Exposure in the Human," in T. M.
Pinkert (ed.), Current Research on the Consequences of Maternal Drug Abuse
(Rockville, MD: National Institute on Drug Abuse, 1985), 48-60.

12. E. E. Hatch and M. B. Bracken, "Effect of Marijuana Use in Pregnancy on
Fetal Growth," American Journal of Epidemiology 124 (1986): 986-993. J.
Kline et al., "Cigarettes, Alcohol and Marijuana: Varying Associations with
Birthweight," International Journal of Epidemiology 16 (1987): 44-51. B.
Zuckerman et al., "Effects of Maternal Marijuana and Cocaine Use on Fetal
Growth," New England Journal of Medicine 320 (1989): 762-768. P. A. Fried
et al., "Marijuana Use During Pregnancy and Decreased Length of Gestation,"
American Journal of Obstetrics and Gynecology 150 (1984): 23-26. R. Hingson
et al., "Effects of Maternal Drinking and Marijuana Use on Fetal Growth and
Development," Pediatrics 70 (1982): 539-546. P. A. Fried and J. E. Makin,
"Neonatal Behavioral Correlates of Prenatal Exposure to Marijuana,
Cigarettes and Alcohol in a Low Risk Population," Neurotoxicology and
Teratology 9 (1987): 1-7. M. D. Cornelius et al., "Prenatal Tobacco and
Marijuana Use Among Adolescents: Effects on Offspring Gestational Age,
Growth, and Morphology," Pediatrics 95 (1995): 738-743. N. Day et al.,
"Prenatal Marijuana Use and Neonatal Outcome," Neurotoxicology and
Teratology13 (1991): 329-334.

13. N. L. Day and G. A. Richardson, "Prenatal Marijuana Use: Epidemiology,
Methodologic Issues, and Infant Outcome," Clinics in Perinatology 18
(1991): 77-91. G. A. Richardson et al., "The Impact of Marijuana and
Cocaine Use on the Infant and Child," Clinical Obstetrics and Gynecology 36
(1993): 302-318. M. D. Cornelius et al. (1995), see Note 12. C. D. Coles et
al., "Effects of Cocaine, Alcohol, and Other Drug Use in Pregnancy on
Neonatal Growth and Neurobehavioral Status," Neurotoxicology and Teratology
14 (1992): 22-33.

14. N. Day et al. (1991), see Note 12.

15. E. E. Hatch and M. B. Bracken (1986), see Note 12.

16. P. A. Fried et al. (1984), see Note 12.

17. K. Tennes et al. (1985), see Note 11.

18. N. L. Day et al., "Effect of Prenatal Marijuana Exposure on the
Cognitive Development of Offspring at Age Three," Neurotoxicology and
Teratology 16 (1994): 169-175.

19. A. P. Streissguth, et al., "IQ at Age 4 in Relation to Maternal Alcohol
Use and Smoking During Pregnancy," Developmental Psychology 25 (1989): 3-11.

20. See Note 18.

21. Center on Addiction and Substance Abuse, Legalization: Panacea or
Pandora's Box (New York, 1995). Drug Watch Oregon, Marijuana Research
Review 2 (1995): 4.

22. L. L. Robison et al., "Maternal Drug Use and Risk of Non-Lymphoblastic
Leukemia Among Offspring," Cancer 63 (1989): 1904-1911.

23. S. Grufferman et al., "Parents' Use of Cocaine and Marijuana and
Increased Risk of Rhabdomyosarcoma in Their Children," Cancer Causes and
Control 4 (1993): 217-224.

24. N. L. Day et al., "The Epidemiology of Alcohol, Marijuana and Cocaine
Use Among Women of Childbearing Age and Pregnant Women," Clinical
Obstetrics and Gynecology 36 (1993): 232-245.

25. S. Grufferman et al., "Environmental Factors in the Etiology of
Rhabdomyosarcoma in Childhood," Journal of the National Cancer Institute 68
(1982): 107-113.

26. National Toxicology Program, Toxicology and Carcinogenesis: Studies of
1-Trans-Delta-9-Tetrahydrocannabinol in F344/N Rats and B6c3F1 Mice
(Rockville, MD: U.S. Department of Health and Human Services, 1996).

27. P. A. Fried and B. Watkinson, "12- and 24-Month Neurobehavioral
Follow-Up of Children Prenatally Exposed to Marijuana, Cigarettes and
Alcohol," Neurotoxicology and Teratology 10 (1988): 305-313.

28. P. A. Fried and B. Watkinson, "36- and 48-Month Neurobehavioral
Follow-Up of Children Prenatally Exposed to Marijuana, Cigarettes and
Alcohol," Developmental and Behavioral Pediatrics 11 (1990): 49-58.

29. Ibid.

30. P. A. Fried et al., "60- and 72-Month Follow-Up of Children Prenatally
Exposed to Marijuana, Cigarettes, and Alcohol: Cognitive and Language
Assessment," Journal of Developmental and Behavioral Pediatrics 13 (1992):
383-391.

31. P. A. Fried et al., "A Follow-Up Study of Attentional Behavior in
6-Year-Old Children Exposed Prenatally to Marijuana, Cigarettes, and
Alcohol," Neurotoxicology and Teratology 14 (1992): 299-311.

32. C. M. O'Connell and P. A. Fried, "Prenatal Exposure to Cannabis: A
Preliminary Report of Postnatal Consequences in School-Age Children,"
Neurotoxicology and Teratology 13 (1991): 631-639.

33. P. A. Fried, "Prenatal Exposure to Marijuana and Tobacco During
Infancy, Early and Middle Childhood: Effects and Attempts at a Synthesis,"
Archives of Toxicology 17 (1995): 240-241.

34. P. A. Fried, "The Ottawa Prenatal Prospective Study (OPPS):
Methodological Issues and Findings-It's Easy to Throw the Baby Out With the
Bath Water," Life Sciences 56 (1995): 2159-2168.

35. National Conference on Marijuana Use: Prevention, Treatment, and
Research, sponsored by the National Institute on Drug Abuse (Arlington, VA:
July 1995).

36. Center for Substance Abuse Prevention, "Marijuana: Its Uses and
Effects," Prevention Pipeline 8, no. 5 (1995): 3-5.

37. P. A. Fried, "Prenatal Exposure to Tobacco and Marijuana: Effects
During Pregnancy, Infancy, and Early Childhood," Clinical Obstetrics and
Gynecology 36 (1993): 319-337.

38. Ibid.

39. P. A. Fried, "Cigarettes and Marijuana: Are There Measurable Long-Term
Neurobehavioral Teratogenic Effects?" Neurotoxicology 10 (1989): 577-584.
N. Day et al., "The Effects of Prenatal Tobacco and Marijuana Use on
Offspring Growth from Birth through 3 Years of Age," Neurotoxicology and
Teratology 14 (1992): 407-414. H. M. Barr et al., "Infant Size at 8 Months
of Age: Relationship to Maternal Use of Alcohol, Nicotine, and Caffeine
During Pregnancy," Pediatrics 74 (1984): 336-341. P. A. Fried and B.
Watkinson (1990), see Note 28. A. P. Streissguth et al. (1989), see Note
19. M. D. Cornelius et al. (1995), see Note 12. J. Kline et al. (1987), see
Note 12. P. A. Fried (1995), see Note 33.

This article is excerpted from Marijuana Myths, Marijuana Facts: A Review
of the Scientific Evidence by Lynn Zimmer, PhD, and John P. Morgan, MD (New
York: Drug Policy Alliance, 1997). Permission to reprint this article was
granted by the Drug Policy Alliance, the nation's leading organization
working to end the war on drugs. For more information, visit
(http://www.drugpolicy.org)www.drugpolicy.org.