New advice warns women against smoking marijuana while pregnant, as the drug could affect the brain of the developing fetus.

Despite the growing trend for marijuana use in the U.S., new advice warns women against smoking marijuana while pregnant, as the drug could affect the brain of the developing fetus.

According to data from the U.S. Centers for Disease Control and Prevention's National Vital Statistics Reports, more than one in five U.S. births now occur in states where marijuana is legal, following moves by many states to legalize medical use for adults as well as decriminalize or legalize recreational use.

However Dr. Leena Nathan, obstetrician-gynecologist at UCLA Health-Westlake Village, states that for pregnant women who use marijuana for relief from the typical ailments related to pregnancy, the drug could have detrimental effects on their unborn child.

According to a report published in the Journal of the American Medical Association, four per cent of the pregnant women surveyed in 2014 reported using marijuana during their pregnancy, with the actual number potentially higher due to underreporting.

Dr. Nathan says that although for some women, using marijuana helps to relieve pain and morning sickness, particularly in the first trimester, and helps aid relaxation and relieve stress and anxiety, research suggests that it is detrimental to the fetus.

During pregnancy, tetrahydrocannabinol, or THC, the active chemical in marijuana can cross the placenta and affect the fetus, affecting the birth weight as well brain function, decreasing the IQ of the child and making it harder for them to pay attention.

Although consuming edible marijuana is sometimes thought to be safer than smoking, Dr. Nathan advises against both while pregnant, pointing out that it is possible to actually increase exposure to THC exposure when eating marijuana, potentially causing even greater harm to the fetus.

Instead, she advises treating the ailments experienced during pregnancy with other, prescribed medications, or non-medicinal treatments such as vitamin B6, doxylamine, ginger chews and ginger teas, physical therapy and acupuncture to help manage sickness and pain.

To alleviate anxiety, Dr. Nathan suggests starting with exercise, advising women to speak with their doctors about which forms of exercise are safest for them.

She also points out the need for further research into the effect of marijuana's potential health consequences for the fetus, including research to determine how often, how much and when in their pregnancy women are using the substance, and how the drug might harm the child after birth through breastfeeding.

However, based on current research and what health professionals know, she concludes that women should not be using marijuana or other recreational drugs during pregnancy.