Continued marijuana smoking can lead to abnormal function of the lungs and airways. Scientists have found signs of lung tissue injured or destroyed by marijuana smoke. Doctors advise pregnant women not to use any drugs because they might harm the growing fetus. One animal study has linked marijuana use to loss of the fetus very early in pregnancy. Some scientific studies have found that babies born to marijuana users were shorter, weighed less, and had smaller head sizes than those born to mothers who did not use the drug.
Smaller babies are more likely to develop health problems.
Other scientists have found effects of marijuana that resemble the features of fetal alcohol syndrome. There are also research findings that show nervous system problems in children of mothers who smoked marijuana. Researchers are not certain whether a newborn baby's health problems, if they are caused by marijuana, will continue as the child grows. Preliminary research shows that children born to mothers who used marijuana regularly during pregnancy may have trouble concentrating. This is a matter for concern, since the THC in the mother's milk is much more concentrated than that in the mother's blood.