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Prenatal cannabis use was associated with a slew of serious adverse maternal health outcomes later in pregnancy, according to a large cohort study.

Compared with non-use, prenatal cannabis use was associated with increased risks of:

• Placental abruption (adjusted risk ratio [aRR] 1.19, 95% CI 1.05-1.36)
• Gestational hypertension (aRR 1.17, 95% CI 1.13-1.21)
• Weight gain greater than guidelines (aRR 1.09, 95% CI 1.08-1.10)
• Preeclampsia (aRR 1.08, 95% CI 1.01-1.15)
• Weight gain less than guidelines (aRR 1.05, 95% CI 1.01-1.08)

A dose-response association was also found with regard to risk of gestational hypertension, with those who used cannabis daily facing the highest risk (aRR 1.24, 95% CI 1.14-1.36), followed by weekly (aRR 1.21, 95% CI 1.11-1.31) versus never-use (P<0.001), reported Kelly Young-Wolff, PhD, MPH, of Kaiser Permanente Northern California in Pleasanton, and colleagues .

"Our study provides timely and important data that adds to the growing body of evidence indicating that cannabis use during pregnancy is not safe," Young-Wolff told MedPage Today.

She added that "while many studies have examined neonatal outcomes, few studies have looked at how prenatal cannabis use affects the health of the pregnant individual," and most of these studies have been "limited to self-reported cannabis use, which is known to underestimate use, and have not adequately accounted for potential confounders, such as noncannabis prenatal substance use."

In total, 6.3% of pregnancies screened positive for prenatal cannabis use, 2.9% by self-report, 5.3% by toxicology testing, and 1.8% by both methods. Most participants didn't know the frequency of cannabis use (3.4%), but 1.5% were monthly or less, 0.7% were weekly, and 0.6% were daily cannabis users. Results were similar when prenatal cannabis use was defined by self-report alone or by toxicology testing.

Cannabis has been legal in California (where the study took place) for medical use since 1996 and for adult use since 2016. Despite health risks, prenatal cannabis use has also gone up in recent years -- especially as more states legalize cannabis. Young-Wolff's own previous work found that cannabis use among pregnant women increased during the early days of the COVID pandemic, and other work has found that cannabis use during and after pregnancy has also increased for people with HIV.

Other recent research has shown an increased risk of infant death with dual cannabis and nicotine use in pregnancy compared to no use, while another study linked prenatal cannabis use with adverse pregnancy outcomes, including small for gestational age, preterm birth, stillbirth, and hypertensive disorders of pregnancy.

Young-Wolff said that clinicians should "provide coordinated, non-stigmatizing care and education to support pregnant individuals in making informed decisions about cannabis use during pregnancy."

, Jamie Lo, MD, of Oregon Health & Science University in Portland, and Catherine Spong, MD, of the University of Texas Southwestern Medical Center in Dallas, noted that the American College of Obstetricians and Gynecologists (ACOG) recommends , though a growing number of women use cannabis to alleviate pregnancy symptoms. They also noted that previously Young-Wolff conducted another study and found that in-utero cannabis exposure was linked to adverse neonatal outcomes, and that many of those outcomes increased in likelihood with more frequent cannabis use.

However, Lo and Spong pointed out, this study didn't compare "outcomes associated with cannabis use prior to and after legalization of recreational cannabis," which happened during the study period, and some of the maternal outcomes studied are not associated with prenatal cannabis use -- specifically placenta previa and accreta.

Also, while the study "adjusted for other noncannabis prenatal substance use (e.g., alcohol, nicotine, opioids, stimulants, and anxiety/sleep medications), it did not specify other substances (e.g., barbiturates, hallucinogens, and ecstasy) that may also confound the study's findings," they said.

Future research should examine the underlying mechanistic pathways, Lo and Spong concluded, as well as outcomes related to co-use of cannabis and other substances in order to inform clinical guideline development and future public health policies.

This population-based retrospective cohort study included 316,722 pregnancies from January 2011 through December 2019 that lasted 20 weeks or longer in 250,221 individuals in Northern California. Prenatal cannabis use was based on universal screening at the start of prenatal care -- usually at around at 8 to 10 weeks' gestation -- via a self-administered questionnaire and urine toxicology test; frequency of use was self-reported.

Mean participant age was 30.6, and 37.4% were white, 26.5% were Asian or Pacific Islander, 26.3% were Hispanic, and 6.3% were Black.

Authors noted a few limitations, including that the sample size was limited to insured pregnant patients in Northern California and may not be generalizable to uninsured patients or those in other states. Additionally, authors couldn't determine whether prenatal use ended at pregnancy recognition and it's possible that urine toxicology tests detected prepregnancy cannabis use. The amount, potency, method, and duration of cannabis use was not assessed. However, Young-Wolff noted the team is currently studying how modes of cannabis use impact maternal health outcomes.

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