The effects of prenatal marijuana use are not as studied or known as alcohol use and tobacco use in infants, but scientists are beginning to understand the risks. Prenatal marijuana exposure has been found to restrict fetal growth, learning disabilities, and memory impairment in offspring.
Two main studies Ottawa Prenatal Prospective Study (OPPS) and Maternal Health Practices and Child Development Study (MHPCD) found that, "Physically, marijuana exposure was not correlated with any changes in head circumference at the mid-gestational period was reported, although a significant reduction in foot length and bodyweight at this gestational period was reported." The MHPCD study also found that with a higher use of marijuana per day in the third trimester of pregnancy resulted in decreased mental scores in the infant around the age of nine months but the difference was found to disappear by the age of 18 months.
The effects of prenatal marijuana exposure affected the verbal and memory areas of the brain in children three to four years old according to both MHPCD and OPPS. These negative associations between memory and verbal reasoning were linked to first and second-trimester marijuana usage. In older children ages 13 to 16-year-olds that were heavily exposed, "displayed deficits in visual memory, visual analysis and the ability to maintain attention." Marijuana consumption during pregnancy does have long-term effects on the child's higher cognitive function.
A study performed at the Texas Tech University School of Medicine looked at the amounts of marijuana found in breast milk. Very low levels of THC were found in breast milk, but the exact amount of THC in breast milk correlated with how much was smoked is unknown. The study also was unsure if the levels of THC in breast milk would increase if the mom smoked more. The first year of a child's life is the most important to brain development, "With chronic use, THC can accumulate in human breast milk to high concentrations. Because a baby's brain is still forming, THC could theoretically affect brain development," stated on Toronto's Hospital for Sick Children website. "THC in marijuana is a very lipophilic compound and gets deposited in the brain and fat tissues of the body. It also has a low molecular weight. Both these properties combine to cause transfer of THC into human milk," explains Sourabh Verma, MD, and neonatologist.
The use of marijuana during pregnancy has profound but variable effects on infants in several areas of development. It affects both growth and brain development, and while genetic and environmental interactions can affect the long-term outcome it can also be the amount of drug ingested during and after pregnancy. While scientists are starting to look at the consumption of marijuana the effects of second-hand smoke in infants also need to be better understood. Further studies also need to focus on only the effects of marijuana exposure, most studies conducted so far have been with patients who are polysubstance users. Mother's need to know about the lack of research and about the current concerns of marijuana use during prenatal, infant, and child stages of development.