**I am not advocating that one should smoke marijuana while pregnant, or that it is beneficial to do so. I am simply presenting information from one examination regarding prenatal exposure to cannabis, and strongly encourage anyone considering the use of cannabis during pregnancy to perform further, extensive research on the matter before making any personal decisions.**
Most of us have been told that women who are pregnant or nursing should entirely avoid the use of cannabis, as it may affect the brain of the developing fetus. While it is implied that the manner in which cannabis use during pregnancy impacts the brain of a developing fetus is negative, scientific evidence proving this implication to be true is vague and virtually lacking – so much so that Colorado lawmakers rejected a bill that would require marijuana dispensaries to post warnings that smoking or ingesting cannabis while pregnant or nursing is dangerous because they struggled “to make sense of incomplete scientific evidence about cannabis use by pregnant or nursing women.”
Since lawmakers were unable to gather sufficient, concrete evidence showing cannabis negatively impacts a developing fetus or nursing infant, their only option was to rely on stories shared by women who had used marijuana while pregnant or nursing, leaving them with no actual scientific basis for passing the bill. As a result, they ultimately opted to “show them [mothers and mothers to be] both sides and let them make the decision with their doctor.” 
Could it be that, yes, consuming marijuana while pregnant affects the brain of a developing fetus …but positively? While studies proving this theory false are lacking, a case study showing that cannabis use during pregnancy positively impacts infants does exist:
Study On The Effects Of Prenatal Cannabis Exposure On Neonates In Jamaica
The dean of nursing at Rush Medical Center of Chicago, Melanie Dreher, studied the effects of prenatal cannabis exposure in Jamaica.  She followed a group of women who smoked cannabis throughout their pregnancies, along with ones who didn’t, and compared neurobehavioral skills of infants from both groups to assess the neurobehavioral effects of prenatal exposure to cannabis.
Approximately one month after birth, the infants with prenatal exposure to cannabis displayed greater physiological stability than those without exposure. After a year, the most significant difference between the two groups was that the neonates who were prenatally exposed to cannabis exhibited stronger social skills (i.e. had better eye contact and were easier to engage with) than those without prenatal exposure to cannabis. Interestingly, infants whose mothers used cannabis the most heavily throughout the duration of their pregnancies had the best overall scores on autonomic stability, quality of alertness, irritability, and self-regulation.
Of course, the decision of whether or not to use cannabis while pregnant is clearly one that is not to be taken lightly. While results of the above study do imply that cannabis use during pregnancy is beneficial, one should always take into account that what may prove true for one person may prove false for another. Therefore, if you are pregnant or planning to become pregnant and are considering smoking or ingesting cannabis throughout the course of your pregnancy, it is certainly wise to take the time to personally research the issue in order to make an informed decision.
1. Wyatt, K. “Colorado Bill on Maternal Pot Use Rejected.” The Cannabist. February 4, 2015. Accessed August 15, 2016 from http://www.thecannabist.co/2015/02/03/maternal-marijuana-use-microscope-colorado/29046/
2. Dreher et al. 1994. Prenatal marijuana exposure and neonatal outcomes in Jamaica: An ethnographic study. Pediatrics 93: 254-260.