Question: Is prenatal cannabis use increasing more rapidly over time among pregnant patients without vs those with co-occurring prenatal substance use?

Findings: In this cross-sectional time-series study using data from 367 138 pregnancies among 281 590 unique pregnant patients screened for prenatal substance use during early pregnancy as part of routine prenatal care in Kaiser Permanente Northern California, rates of prenatal use of only cannabis increased faster than rates of use of cannabis and 1 other substance, while rates of use of cannabis and 2 or more substances decreased.

Meaning: This study suggests that increases in prenatal cannabis use may be associated in part with pregnant individuals who use only cannabis and no other substances, which could reflect growing acceptability of cannabis use and decreasing