Pregnancy
Studies have found that children of marijuana-smoking mothers more frequently suffer from permanent cognitive deficits, concentration disorders, hyperactivity, and impaired social interactions than non-exposed children of the same age and social background.[87][88] A recent study with participation of scientists from Europe and the United States, have now identified that endogenous cannabinoids, molecules naturally produced by our brains and functionally similar to THC from cannabis, play unexpectedly significant roles in establishing how certain nerve cells connect to each other. The formation of connections among nerve cells occurs during a relatively short period in the fetal brain. The study tries to give a closer understanding of if and when cannabis damages the fetal brain[89][90].[91]

Other studies on Jamaica have suggested that cannabis use by expectant mothers does not appear to cause birth defects or developmental delays in their newborn children.[92][93] In a study in 1994 of Twenty-four Jamaican neonates exposed to marijuana prenatally and 20 non exposed neonates comparisons were made at 3 days and 1 month old, using the Brazelton Neonatal Assessment Scale, including supplementary items to capture possible subtle effects. Results showed there were no significant differences between exposed and nonexposed neonates on day 3. At 1 month, the exposed neonates showed better physiological stability and required less examiner facilitation to reach organized states. The neonates of heavy-marijuana-using mothers had better scores on autonomic stability, quality of alertness, irritability, and self-regulation and were judged to be more rewarding for caregivers. This work was supported by the March of Dimes Foundation.[94]


[edit] Lung cancer
Wikipedia.

I personally would not advise smoking of anything during pregnancy. I have seen many birth defects in babies. Hell my own brother is half stupid because of my dumbass mother. Do what you will, but think first.