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?

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

Researchers from Australia analyzed 14 studies involving nearly 400,000 pregnant women and their babies conducted over the past 20 years. 

They found that being exposed 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 rising fast in the US.

The review said the association between cannabis and the disorders was 'not well understood', but previous research has indicated that exposure in the womb leads to genetic changes to the baby.

Researchers in Australia found that pregnant women who use marijuana were more likely to have children diagnosed with ADHD and autism

The graph above from the new Rutgers study shows autism prevalence estimates 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 intellectual disabilities rose more steeply (shown by the blue line) than those who do not (shown by the green line)

The team called for increased interventions for children who have been exposed to cannabis and for pregnant women to steer clear of the substance. 

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

Some 24 states allow the use of marijuana recreationally and 38 allow its medical use.

In some cases of miscarriage or stillbirth where the mother-to-be was using marijuana, they can be found guilty of 'chemical endangerment of the fetus', with a 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, which were conducted between 1999 and 2022 and included 203,783 participants.

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

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

A 2022 study by Perinatal Services British Columbia found marijuana use during pregnancy was most commonly linked to low birthweight, preterm birth, congenital defects, gestational diabetes, and increased risk of C-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 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 alters the amount of happiness chemical dopamine that the brain produces, which could lead to cognitive impairment and issues regulating emotions. 

It's also believed that when a person ingests marijuana during their pregnancy, tetrahydrocannabinol, also known as THC, and other chemicals pass to the baby through the mother's placenta, which supplies the baby with its nutrition and oxygen through the umbilical cord. 

The researchers noted that the review has several limitations, namely the small and non-diverse 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 of autism and ADHD diagnoses. 

READ MORE: Pregnant women smoking marijuana say DRUG helps with pain and nausea, but experts say it could lead to host of childhood issues 

Despite the harmful side effects, some pregnant women are refusing to give up marijuana use while pregnant. 

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

A similar rise has been seen nationally - with rates increasing from one in 150 in 2000 to one in 54 in 2016. 

And ADHD diagnoses in adults, particularly women in their 20s and 30s, are surging across the UK, with an increase of 20 percent in just one year.  

Mountains of emerging research has suggested that smoking weed while pregnant could have lasting consequences for both mother and baby.

Last year, researchers from the University of Utah found that babies exposed to cannabis while in utero were 1.5 times more likely to have low birth weight compared to 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 the moms-to-be.

Dr Robert Silver, professor of obstetrics and gynecology at the university, said: 'Cannabis use is not safe... you shouldn't use cannabis during pregnancy.' 

A study in the American Journal of Obstetrics & Gynecology suggested using cannabis in the first six to 14 weeks of pregnancy could lead to several adverse birth effects, including poor fetal growth, stillbirth, and an increased risk of pregnancy-related high blood pressure, which could be life threatening.  

Additionally, research in the journal Frontiers in Pediatrics found when mothers used marijuana during the first three months of pregnancy, their babies were on average one-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 health research at Central Michigan University, told CNN: 'Low birth weight is one of the strongest predictors of a child’s health and development long-term.

'These kids are more prone 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.