Table 1.

Studies assessing cognition in infants and toddlers (up to 24 months).

Investigators	Cohort	Domain tested	Participants	Exposure	Findings	Caveats
Fried and Watkinson, 1988	OPPS	Overall development {BSID, Mental and psychomotor development index, and Infant behavior record [(Primary cognition composite score composed of object orientation, goal directedness, attention span, reactivity, and vocalization subtests), (Auditory score composed of responsiveness to persons, examiner and mother, reactivity, and listening to sounds subtests), (Visual score composed of responsiveness to objects, attention span, manipulating, and sights-looking subtests)]} 24 months only: Language development [Reynell developmental languages scales, (Comprehension and expression subtests)] Total no. of outcome measures = 41	12 and 24 month children of women who reported MJ use during pregnancy 12 month olds: (heavy MJ: N = 17; CTL: N = 162) 24 month olds: (heavy MJ: N = 18; CTL: N = 100)	MJ use self-reported throughout for each trimester Categories: Exposed Heavy = AWJ > 5	12 month olds: Prenatal MJ exposure was associated with higher cognition scores (BSID: primary cognition composite)† No other differences were observed	Relatively small number of participants studied in the heavy MJ-exposed group Mothers reported tobacco cigarette smoking, and alcohol use. It is not clear whether this was controlled for Maternal MJ use was determined exclusively from self-report
Richardson et al., 1995	MHPCD	Overall development (BSID, Mental and psychomotor development index) Total no. of outcome measures = 36	9 and 19 month children of women who reported MJ use during pregnancy 9 month olds: (heavy MJ: N = 73; moderate MJ: N = 31; light MJ: N = 104; CTL: N = 312) 19 month olds: (heavy MJ: N = 57; moderate MJ: N = 34; light MJ: N = 119; CTL: N = 358)	MJ use self-reported at 4th & 7th pregnancy months and at 24–28 h post-delivery for each trimester Categories: Exposed by trimester Light = 0 < ADJ < 0.4 Moderate = 0.4 ≤ ADJ < 1 Heavy = ADJ ≥ 1	9 month olds/3rd trimester: Heavy prenatal MJ exposure group performed more poorly on cognitive development (BSID: mental development index)* Prenatal MJ exposure was associated with lower cognition scores (BSID: mental development index)* No other differences were observed	When adjusted mean cognitive scores of all groups studied were compared against a normative data set by the authors, they exceeded the average range Mothers reported tobacco cigarette smoking, and alcohol use, but this was controlled for Maternal MJ use was determined exclusively from self-report
Singer et al., 1999	CWRUS	Visual recognition memory (Fagan test of infant intelligence, novelty score for four problems) Total no. of outcome measures = 4	Up to 2 month children of women who self-reported MJ use during pregnancy: (MJ: N = 58; CTL = 16)	MJ use self-reported at “as soon as possible” post-delivery period Also, maternal and infant urine analyzed for cannabinoids; infant meconium was analyzed for THC Categories: Exposed	No differences were observed	Cognitive scores were not reported Mothers reported other drug use. It is not clear whether this was controlled for
Singer et al., 2002	CWRUS	Overall development (BSID-II, Mental and psychomotor development index) Total no. of outcome measures = 6	6, 12, and 24 month children of women who reported MJ use during pregnancy: (MJ: N = 102; CTL = 313)	MJ use self-reported at “as soon as possible” post-delivery period Also, maternal and infant (in some cases) urine analyzed for cannabinoids; infant	No differences were observed	Cognitive scores were not reported Mothers reported tobacco cigarette smoking, alcohol, and cocaine use, but this was controlled for meconium was analyzed for cannabinoids Categories: Exposed
Noland et al., 2003a	CWRUS	Goal-directed action (A-not-B task); Overall development (BSID-II, Mental and psychomotor development index, and behavioral rating scale) Total no. of outcome measures = 4	9 to 12 month children of women who reported MJ use during pregnancy: (MJ: N = 9; CTL: N = 42)	MJ use self-reported 2 weeks post-delivery Also, maternal and infant urine analyzed for THC Categories: Exposed	No differences were observed	Cognitive scores were not reported Mothers reported tobacco cigarette smoking, alcohol, and cocaine use, but this was controlled for Relatively small number of participants studied in the MJ-exposed group
Singer et al., 2005	CWRUS	Visual recognition memory (Fagan test of infant intelligence, novelty score, percent performing in risk range, familiarization phase average looking time, and trial phase average looking time) Total no. of outcome measures = 24	6 and 12 month children of women who reported MJ use during pregnancy: (MJ: N = 107; CTL: N = 245)	MJ use self-reported 2 weeks post-delivery Also, maternal and infant urine analyzed for THC Categories: Exposed by trimester	6 month olds: Severity of prenatal MJ exposure in the 3rd trimester was associated with shorter average looking times† No other differences were observed	Faster looking times did not relate to visual recognition memory Mothers reported tobacco cigarette smoking, alcohol, and benzodiazepine use, but this was controlled for
Richardson et al., 2008	MHPCD	Overall development {BSID, Mental and psychomotor development index, and Infant behavior record [(Primary cognition composite score composed of object orientation, goal directedness, attention span, reactivity and vocalization subtests), (Auditory score composed of responsiveness to persons, examiner and mother, reactivity, and listening to sounds subtests), (Visual score composed of responsiveness to objects, attention span, manipulating, and sights-looking subtests)]} Total no. of outcome measures = 57	16 month children of women who reported MJ use during pregnancy: (MJ: N = 85; CTL: N = 176)	MJ use self-reported at 7th pregnancy month and at 24 h post-delivery for each trimester Categories: Exposed by trimester	No differences were observed	Cognitive scores were not reported Mothers reported tobacco cigarette smoking, and alcohol use, but this was controlled for Maternal MJ use was determined exclusively from self-report

ADJ, Average daily joints; AWJ, Average weekly joints; BSID/BSID-II, Bayley scales of infant development 1st and 2nd editions; CTL, Control group; CWRUS, Case Western Reserve University Study; MHPCD, Maternal Health Practices and the Child Development Study; MJ, Marijuana group; NIAAA, National Institute on Alcohol Abuse and Alcoholism; NIDA, National Institute on Drug Abuse; OPPS, Ottawa Prenatal Prospective Study; THC, Tetrahydrocannabinol.

^*Negative associations on cognitive outcomes,

^†Positive associations on cognitive outcomes.