Inadequate or Inconsistent Data
"Since marijuana crosses the placenta, it is reasonable to think that it may have a direct, adverse effect on the fetal brain or on fetal growth, but the small number of studies performed to date have failed to identify major birth defects or a consistent effect on neurobehavioral function. Results regarding the relationship of prenatal marijuana exposure to lowered birth weight are inconsistent."
Zuckerman, Barry, "Drug-Exposed Infants: Understanding the Medical Risk," The Future of Children, Spring 1991, Volume 1, Number 1, p. 28. Citing Institute of Medicine, Preventing Low Birthweight: Summary, National Academy Press, Washington, D.C., 1985.