Table 1.

Comparison of characteristics of 3 important prospective longitudinal studies

CHARACTERISTIC	OPPS9	MHPCD2,10	GENERATION R1,11
Year study began	1978	1982	2001
Population	Caucasian, primarily middle class	Largely African American (57%) and single (71%), with low SES	Multiethnic cohort; slightly higher SES compared with nonresponders or incomplete responders
Recruitment	Self-referral for study participation based on posters in prenatal clinics and information from prenatal providers	Actively recruited from an inner-city prenatal clinic in the 4th or 5th mo of pregnancy	Enrolled based on residence in the study area with a due date during recruitment. Recruited from early pregnancy until birth
Cannabis-exposed population and total sample size, n/N	78/698	307/763	220/7531
Polysubstance use	Yes: tobacco (21%) and alcohol (76%)	Yes: alcohol (65%), tobacco (53%), cocaine (3.6%), and other illicit drugs (8.6%)	Yes: alcohol (31%), tobacco (39%), and other substances (4.5%)
Method of data collection to determine cannabis use	Repeated interviews largely within each woman’s home by the same trained, female interviewer for each interview	Standardized interviews	Self-reported questionnaires
Categorization of cannabis exposure	Nonuser, light user (≤ 1 joints/wk), moderate user (2–5 joints/wk), or heavy user (> 5 joints/wk)	Based on ADJ: light (0–0.4 ADJ), moderate (0.5–1 ADJ), or heavy (> 1 ADJ) use	Nonuse, occasional (monthly), moderate (weekly), or heavy (daily) use
Cannabis use measured	Each trimester	First, second, and third trimester, and 8 mo, 18 mo, and 36 mo postpartum	Prepregnancy, early pregnancy, and late pregnancy
Retention rate	At 22 y only 49 (63%) of the group exposed to cannabis remained	Of the total sample, 636 (83%) followed up at 10 y, 580 (76%) at 14 y, and 608 (80%) at 22 y	Follow-up rates for the total sample at 6 y exceed 80% for most measures
Limitations	Small sample with small number of heavy (n = 25) and moderate (n = 37) users Low-risk sample Self-reported use, although used the same interviewer for all interviews in an effort to build rapport	Large, high-risk sample with potential for multiple confounding variables Substantial polysubstance use with alcohol, tobacco, cocaine, and other illicit substances Self-reported use of cannabis	Likely highest-potency THC products owing to increasing potency over time and increased potency of Dutch cannabis products Self-reported use of cannabis Use of self-report questionnaires skewed the sample to a higher SES and more educated sample compared with nonresponders or incomplete responders

ADJ—average daily joints, MHPCD—Maternal Health Practices and Child Development, OPPS—Ottawa Prenatal Prospective Study, SES—socioeconomic status, THC—tetrahydrocannabinol.