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Adverse outcomes in pregnancy appeared more frequent if the child-to-be was exposed to cannabis in the early stages of pregnancy, retrospective data from a multicenter study suggested.

Of more than 9,000 pregnancies, the primary composite endpoint of small for gestational age, medically indicated preterm birth, stillbirth, or hypertensive disorders of pregnancy occurred in 27.4% of the cannabis-exposed group compared with 18.1% of the non-exposed group (P<0.001), reported Torri Metz, MD, MS, of the University of Utah in Salt Lake City, at the Annual Pregnancy Meeting.

The study was ancillary to a prospective nulliparous cohort study involving women recruited at eight U.S. centers from 2010 to 2013, and used frozen urine samples collected at 6 to 14 weeks' gestation to examine exposure to cannabis.

"We wanted to look specifically at cannabis use early in pregnancy because that's when the placenta is forming, and a lot of information we currently have indicates that cannabis use does affect the placenta," said Metz. "With recreational marijuana use becoming legal in more states, we need better data because patients are interested in understanding the risk of cannabis use in pregnancy so they can make an informed decision."

Metz explained that the natural endocannabinoid system regulates placenta development, raising concerns that the addition of cannabis could compromise that highly regulated system.

Among the individual components of the primary endpoint, most were significantly worse among the group exposed to cannabis:

• Small for gestational age: 9.5% vs 4.1% (P<0.001)
• Hypertensive disorders of pregnancy: 15.9% vs 13% (P=0.049)
• Stillbirth: 1.5% vs 0.5% (P=0.003)
• Medically indicated preterm birth: 5.2% vs 3.9% (P=0.141)

According to the , 37 states have legalized marijuana for medical purposes and 21 states have legalized it for recreational use.

Based on the findings of the study, "clinicians should counsel their patients that marijuana use should be discontinued during pregnancy," Cornelia Graves, MD, medical director of Tennessee Maternal Fetal Medicine and co-director of the Collaborative Perinatal Cardiac Center at the University of Tennessee in Nashville, told MedPage Today. "Patients should also be counseled that early use may increase their risk of pregnancy complications."

"It should be noted that the counseling for marijuana use in pregnancy is the same counseling as we currently use for tobacco use in pregnancy -- cessation is recommended in order to prevent poor pregnancy outcomes," added Graves, who was not involved with the study.

Metz noted that most of the women in the study had smoked marijuana or other cannabis products, since cannabis edibles had not penetrated much of the market during the time frame that the frozen urine samples had been collected.

She and her colleagues accessed the data collected in the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (). Exposure to cannabis was ascertained by urine immunoassay for 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH), and positive results were confirmed with liquid chromatography tandem mass spectrometry.

Of the 10,038 participants in the trial, the researchers included data from 8,717 women unexposed to cannabis and 540 women whose urine indicated exposure during their first clinic visit.

The women who were exposed to cannabis tended to be younger -- only 8% were over age 30 when giving birth, compared with 37% of the women who were not showing signs of cannabis exposure; those exposed were also more likely to be non-Hispanic Black, single and never married, and to have public insurance coverage.

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