The number of pregnant women using marijuana has risen in California since the state relaxed its drug laws, a new study has found.
The increase was especially sharp among young women, rising from 12.5 percent to nearly 22 percent for mothers to be under the age of 24, in the years between 2009 and 2016.
Overall there was a rise from around 4 percent to around 7 percent, researchers from healthcare consortium, Kaiser Permanente Northern California, found.
Researchers examined screening data that encompassed some 280,000 women who were tested between 2009 and 2016.
The findings were published in the Journal of the American Medical Association .
The report does not directly draw a connection between the increase and laxer marijuana laws. But the period covered coincides with California steadily loosening penalties for marijuana use, mirroring a national trend.
But the study's author's wrote that "continued monitoring of trends, exposure timing, and offspring outcomes is important as marijuana potency rises in an increasingly permissive legal landscape."
In 2010, then-Governor Arnold Schwarzenegger signed a law downgrading possession of an ounce or less from a misdemeanour to an infraction, meaning a punishment of a fine, rather than imprisonment.
In pictures: 4/20 Marijuana world ralliesShow all 26 1 /26In pictures: 4/20 Marijuana world rallies
In pictures: 4/20 Marijuana world rallies A man wears a marijuana leaf mask during the annual 4/20 cannabis culture celebration at Sunset Beach in Vancouver, British Columbia
AP
In pictures: 4/20 Marijuana world rallies A lady smokes marijuana on Parliament Hill on 4/20 in Ottawa, Ontario
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In pictures: 4/20 Marijuana world rallies James Reed smokes a joint during the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies People sign a 4/20 sign on Parliament Hill on in Ottawa, Ontario
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In pictures: 4/20 Marijuana world rallies A woman smokes marijuana on Parliament Hill on 4/20 in Ottawa, Ontario. Polling released showed strong support in Canada for a government drive to legalise recreational use of marijuana, but many would like the proposed minimum age for consumption to be raised. Sixty-three percent of respondents told the Angus Reid Institute they support legalisation
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In pictures: 4/20 Marijuana world rallies A man smokes marijuana during the annual 4/20 marijuana rally on Parliament Hill in Ottawa, Ontario, Canada
Reuters
In pictures: 4/20 Marijuana world rallies Demonstrators smoke marijuana during the '4/20 Santiago' rally in favour of legalisation in front of the La Moneda presidential palace in Santiago, as part of the Global Marijuana March which is being held in hundreds of cities worldwide
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In pictures: 4/20 Marijuana world rallies People play with a mock marijuana joint during a 4/20 party to demand legalisation and to celebrate marijuana culture outside the Senate building in Mexico City, Mexico
Reuters
In pictures: 4/20 Marijuana world rallies Adam Eidinger, co-founder of DCMJ, hands out free marijuana joints to DC residents who worked on Capitol Hill as part of the 1st Annual Joint Session to mark '4/20' day and promote legalising marijuana on Capitol Hill in Washington, DC
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In pictures: 4/20 Marijuana world rallies
In pictures: 4/20 Marijuana world rallies Police arrest Rachel Ramone Donlan after she handed out free marijuana joints to DC residents who worked on Capitol Hill as part of the 1st Annual Joint Session to mark '4/20' day and promote legalising marijuana on Capitol Hill in Washington, DC
AFP/Getty Images
In pictures: 4/20 Marijuana world rallies Police arrest Rachel Ramone Donlan after she handed out free marijuana joints to DC residents who worked on Capitol Hill as part of the 1st Annual Joint Session to mark '4/20' day and promote legalising marijuana on Capitol Hill in Washington, DC
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In pictures: 4/20 Marijuana world rallies Thousands of people gather to smoke marijuana during the '420 Santiago'rally in front of the La Moneda presidential palace in Santiago
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In pictures: 4/20 Marijuana world rallies People attend the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies Kevin Barron and Lasean Moore of Raleigh, North Carolina, share a joint during the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies Nic Ruhl takes a pull on a giant hand rolled joint at precisely 4:20pm MDT during the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies Various cannabis paraphernalia on display at a vendor's stall during the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies Mo Banez, of Austin, Texas, lights a joint during the Denver 420 Rally at Civic Center Park in Denver, Colorado
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In pictures: 4/20 Marijuana world rallies A man displays a large container of cannabis during the Denver 420 Rally at Civic Center Park in Denver, Colorado. The rally, held annually, is a celebration of both the legalisation of cannabis and cannabis culture. Colorado is one of twenty-six U.S. states along with the District of Columbia that has legalised the use of cannabis either recreationally or medically
AFP/Getty Images
In pictures: 4/20 Marijuana world rallies Sitting in small groups on mats shaded by trees in the Rose Garden just across from the Knesset, participants lit up as the clock struck 4:20 for the local version of the traditional worldwide April 20 pro-marijuana events, known as '420' rallies
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In pictures: 4/20 Marijuana world rallies An Israeli smokes a marijuana joint in Jerusalem during a rally at the Rose garden
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In pictures: 4/20 Marijuana world rallies Sitting in small groups on mats shaded by trees in the Rose Garden just across from the Knesset, participants lit up as the clock struck 4:20 for the local version of the traditional worldwide April 20 pro-marijuana events, known as '420' rallies
Getty Images
In pictures: 4/20 Marijuana world rallies An Israeli girl poses with a mock marijuana joint in Jerusalem during a rally at the Rose garden, to celebrate 420 and to express their defiance of current laws
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In pictures: 4/20 Marijuana world rallies aelis pass around a marijuana joint in Jerusalem during a rally at the Rose garden, to celebrate 420 and to express their defiance of current laws
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In pictures: 4/20 Marijuana world rallies An Israeli smokes a marijuana joint in Jerusalem during a rally at the Rose garden, to celebrate 420 and to express their defiance of current law
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In pictures: 4/20 Marijuana world rallies An Israeli smokes a marijuana joint in Jerusalem on April 20, 2017 during a rally opposite the Knesset to celebrate 420 and express defiance of current laws
AFP/Getty Images
Californians voted to legalise recreational use of the drug in 2016. The first shops authorised to sell the drug are set to open in the new year.
Opponents of decriminalising or legalising cannabis warn it will undermine public health, pointing in particular to the risk of increased use among teenagers whose developing brains are more vulnerable.
California’s initiative requires marijuana products to bear labels warning of potential health hazards, including that marijuana use while pregnant or breastfeeding could be harmful.
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