Using weed during pregnancy may raise risk of child having autism or ADHD by 30%, large review warns – is this partly why rates of both conditions are rising in US?

Marijuana use during pregnancy could lead to an increased chance of the baby being born with autism or ADHD, a first-of-its-kind study suggests.

Researchers from Australia analyzed 14 studies involving nearly 400,000 pregnant women and their babies over the past two decades.

They found that exposure to marijuana in the womb was linked to an up to 30 percent increased chance of the child being diagnosed with autism or ADHD – two conditions that are rapidly increasing in the US.

The review said the association between cannabis and the conditions was ‘not well understood’, but previous research has shown that exposure in the womb leads to genetic changes in the baby.

The above graph from the new Rutgers study shows estimates of the prevalence of autism per 1,000 eight-year-old children in New Jersey overall and by intellectual ability. The proportion of eight-year-olds diagnosed with autism who do not have an intellectual disability has increased more (shown by the blue line) than those who do not (shown by the green line)

The team called for more interventions for children exposed to cannabis and for pregnant women to avoid the substance.

The findings come as data shows more young people are smoking weed than ever before, with use among pregnant women doubling between 2002 and 2017. The last year’s data is available.

About 24 states allow recreational use of marijuana and 38 states allow its medical use.

In some cases of miscarriage or stillbirth where the expectant mother used marijuana, they can be found guilty of “chemical endangerment of the fetus,” with a prison sentence of up to 99 years.

The new review included 14 studies. Ten of these focused on the effect of prenatal cannabis use on ADHD, conducted between 1999 and 2022 and involving 203,783 participants.

The rest looked at the link between cannabis and autism. These were conducted between 2020 and 2023 and included 173,035 participants.

They found that using marijuana during pregnancy led to a 13 percent increased risk of children developing ADHD, as well as a 30 percent increased risk of autism.

A 2022 study by Perinatal Services British Columbia found that marijuana use during pregnancy was most commonly associated with low birth weight, preterm birth, birth defects, gestational diabetes and an increased risk of cesarean section.

Cannabis is the most commonly used federally illegal drug among pregnant women in the United States, with use among pregnant women doubling between 2002 and 2017, the latest year of data is available.

“The mechanism of how prenatal cannabis use may cause neurodevelopmental disorders such as ADHD symptoms and ASD in human offspring is not well understood,” the researchers wrote.

The team noted that studies in animals suggested that cannabis changes the amount of happiness chemical dopamine the brain produces, which could lead to cognitive impairment and problems regulating emotions.

It is also believed that when someone ingests marijuana during pregnancy, tetrahydrocannabinol, also known as THC, and other chemicals pass to the baby through the mother’s placenta, which provides nutrition and oxygen to the baby through the umbilical cord.

The researchers noted that the review has several limitations, namely the small and undiversified number of studies. Additionally, they did not look at how much marijuana the women consumed or how they used it, such as smoking or edibles.

The findings come amid a rise in autism and ADHD diagnoses.

For example, a Rutgers University study published last year found that between 2000 and 2016, the rate of ASD diagnoses in children under the age of eight in New York and New Jersey increased from 10 per 1,000 to 30 per 1,000.

A similar increase has been observed nationally: from one in 150 in 2000 to one in 54 in 2016.

And the number of ADHD diagnoses in adults, especially in women in their 20s and 30s, is rising across Britain, with a 20 percent increase in just one year.

Mountains of emerging research show that smoking weed during pregnancy can have lasting effects on both mother and baby.

Last year, researchers at the University of Utah found that babies exposed to cannabis in the womb were 1.5 times more likely to have low birth weight than babies who were not.

That team also found a 30 percent increased risk of medically induced preterm birth, stillbirth and pregnancy-related high blood pressure in expectant mothers.

Dr. Robert Silver, professor of obstetrics and gynecology at the university, said: ‘Cannabis use is not safe… you should not use cannabis during pregnancy.’

A study in the American Journal of Obstetrics and Gynecology suggested that cannabis use in the first six to fourteen weeks of pregnancy could lead to several adverse birth effects, including poor fetal growth, stillbirth and an increased risk of pregnancy-related hypertension, which could be life-threatening.

Additionally, research in the journal Frontiers in Pediatrics found that when mothers used marijuana during the first three months of pregnancy, their babies were, on average, a third of a pound smaller than babies whose mothers did not use cannabis.

Dr. Beth Bailey, lead author of that study and director of population research at Central Michigan University, told CNN: “Low birth weight is one of the strongest predictors of a child’s long-term health and development.

‘These children are more susceptible to developmental delays, higher rates of ADHD, learning disabilities and have higher rates of emotional problems.’

The new study was published this month in the Journal of Psychiatric Research.