A flurry of research papers published this year has simultaneously documented a rise in the use of cannabis during pregnancy and offered more data about its potential harms. This confluence of findings is concerning and highlights the importance of screening our patients for cannabis use and engaging with them in a way in which we can maintain their trust and their commitment to prenatal care.
A retrospective cohort study involving 661,617 women in Ontario found a significant association between self-reported cannabis use in pregnancy and an increased risk of preterm birth (relative risk, 1.41), as well as a greater likelihood of small-for-gestational-age babies (RR, 1.53), placental abruption (RR, 1.72), and transfer to neonatal intensive care (RR, 1.40).1 The study, reported in JAMA in July 2019, carefully matched users with nonusers who had the same characteristics – for example, tobacco use or not.
This new information builds upon other meta-analyses that have demonstrated a decrease in birth weight and greater admittance to the neonatal ICU associated with cannabis use in pregnancy – and it supplements what some research suggests about long-term neurologic development and a potentially increased risk of attention and behavioral problems. Other outcomes that have been noted in long-term neurologic studies of children who were exposed to cannabis in utero include impaired visual acuity, verbal reasoning and comprehension, and short-term memory.2
Increases in use were recently documented in two studies. One, an analysis of data from the National Survey on Drug Use and Health (NSDUH) published in JAMA in June 2019, showed that, between 2002-2003 and 2016-2017, the use of cannabis “in the past month” increased from 3.4% to 7.0% among pregnant women overall, and from 6% to 12% during the first trimester.3
The use of cannabis on a daily or near-daily basis, moreover, increased from 0.9% to 3% among pregnant women overall and from 2% to 5% during the first trimester. The data were collected during face-to-face interviews and were adjusted for age, race/ethnicity, and family income.
In the second study – a cross-sectional study of 367,403 pregnancies among women who filled out a questionnaire on cannabis use during standard prenatal care at Kaiser Permanente Northern California – the adjusted prevalence of use in the year before pregnancy increased from 7% in 2009 to 13% in 2017, and the adjusted prevalence during pregnancy increased from 2% to 3%.4
As in the NSDUH analysis, daily use increased most rapidly (compared with weekly or monthly) such that, by 2017, 25% of those who reported using cannabis in the year before pregnancy – and 21% of those who used cannabis during pregnancy – were daily users. It is notable that Kaiser’s population is diverse in all respects, and that the annual relative rates of increase in cannabis use before and during pregnancy (at each level of frequency) were consistent across racial/ethnic and household income groups.
It’s also worth noting that, in earlier research covering a similar time period (2009-2016), the investigators found significant increases in use via urine toxicology testing that occurs at the first prenatal visit at Kaiser. The increase found through questionnaires, therefore, reflects more than a greater willingness to self-report.