Pregnancy

They also discovered that prenatal marijuana use was associated with a 50 percent increased chance of low birth weight regardless of tobacco use during pregnancy. “Growing evidence suggests prenatal cannabis exposure has a detrimental impact on offspring brain function starting in the toddler years, specifically issues related to attention deficit disorder,” Crume said. “But much of the research on the effects of prenatal cannabis on neonatal outcomes was based on marijuana exposures in the 1980s and 1990s which may not reflect the potency of today’s cannabis or the many ways it is used.”

In a new study, researchers in London, Ontario found that women who used marijuana while pregnant were almost three times more likely to have an infant with low birth weight than women who did not use marijuana.

Here are just a few of the health effects you may want to know:

• Marijuana use directly affects the brain—specifically the parts of the brain responsible for memory, learning, and attention.
• The compounds in marijuana can affect the circulatory system and may increase the risk of heart attacks and strokes.
• Smoking marijuana can lead to a greater risk of bronchitis, cough, and phlegm production.
• Marijuana users are significantly more likely than nonusers to develop chronic mental disorders, including schizophrenia. Schizophrenia is a type of mental illness where people might see or hear things that aren't really there (hallucinations).
• Eating foods or drinking beverages that contain marijuana have some different risks than smoking marijuana, including a greater risk of poisoning.
• About 1 in 10 marijuana users will become addicted. For people who begin using before the age of 18, that number rises to 1 in 6.
• Some research shows that using marijuana while you are pregnant[288 KB] can cause health problems in newborns—including low birth weight and developmental problems.
• Marijuana use can slow your reaction time and ability to make decisions when driving[271 KB].

Summary: Cannabis use during pregnancy is associated with abnormal brain structure in children, according to a new study. Compared with unexposed children, those who were prenatally exposed to cannabis had a thicker prefrontal cortex, a region of the brain involved in complex cognition, decision-making, and working memory.

Children whose mothers use marijuana during pregnancy have a higher risk of stunted growth and of developing ADHD, anxiety, and depression later in life.
When THC enters the body, it interferes with endocannabinoid’s actions, competing with it for binding sites on target cells and generally getting its way.

My main finding is that it's primarily women who were younger when they become mothers who do continue to use marijuana overtime. Also women who are depressed over longer periods of time, women who smoke, women who use more than the recommended amount of alcohol are more likely to continue to use marijuana while pregnant as well as when they're raising their children. So the take-home messages is to ask women about marijuana use. We know that marijuana use is considered more and more acceptable by women and that they may continue to use while they are pregnant and while they are having children.

Given these statistics.... is legalization worth the consequences....
Cannabis has been found to be the most frequently used drug in the U.S. after alcohol, tobacco and caffeine. 
The risk of developing addiction associated with cannabis use has been reported to increase to about 17% among those who start using marijuana in adolescence, and to 25-50% among those who smoke marijuana daily.
The long-term effects of marijuana use include altered brain development and cognitive impairment, including impaired neural connectivity in specific brain regions, decreased activity in prefrontal regions, and reduced volumes in the hippocampus.
Cannabis is most commonly consumed through smoking, a route of drug delivery that predictably has a variety of negative effects on pulmonary function. Smoke from marijuana combustion has been shown to contain a number of carcinogens and cocarcinogens, as well as many of the toxins, irritants, and carcinogens as tobacco smoke.  Additionally, marijuana smokers tend to inhale more deeply and hold their breath longer than cigarette smokers, which leads to a greater exposure per breath to “tar” (the carcinogenic solids in smoke). Regular smoking of marijuana, in the absence of tobacco, produces visible and microscopic injury to the large airways
http://www.asam.org/docs/default-source/publicy-policy-statements/mariju...

Studies show that children exposed to marijuana in utero have lower scores on tests of visual problem-solving, visual and motor coordination, and visual analysis, compared with children not exposed to the drug, the report states. Prenatal marijuana exposure also has been associated with decreased attention span and behavioral problems. The nervous system of a human fetus can respond to the chemicals in marijuana within 14 weeks of gestation, and studies have shown that 14-year-olds are more likely to be marijuana users if their mothers used the drug during pregnancy.

State of the Science   190 resources
Several problems are associated with marijuana use during pregnancy, because prenatal exposure influences brain development and can result in permanent cognitive impairment. [35] Cognitive deficits resulting from prenatal exposure include inattention; impulsivity; and impairment in learning, memory, and certain aspects of executive functioning. [36] In addition, prenatal exposure to cannabis has been associated with reduction of fetal growth. [37]
For many years, the myth of smoked cannabis being "healthier" or "no worse" than smoked tobacco was perpetuated by pro­marijuana groups. Both smoked cannabis and tobacco contain approximately 4000 chemicals and that these chemicals are essentially identical in both plants.In another recent review, [23] the authors concluded that "smoking of cannabis is not medically recommended due to the potential respiratory tract, dangers of noxious compounds such as polycyclic aromatic hydrocarbons, tar and carbon monoxide."
 
 

Appendix

Changes in Marijuana Use Patterns, Systematic Literature Review, and Possible Marijuana-Related Health Effects

Recent attention has been focused on the long-term impact of cannabis exposure, for which experimental animal studies have validated causal relationships between neurobiological and behavioral alterations during the individual's lifetime.