Maternal Marijuana Exposure and Birth Weight: An Observational Study Surrounding Recreational Marijuana Legalization

Abstract

Objective To study the relationship between prenatal marijuana and infant birth weight using natural cohorts established before, during and after the 20-month lapse between legalization and legal recreational sales in Washington State. Study Design Over 5 years, 5,343 pregnant women with documented urine drug screen (UDS) results delivered at Tacoma General Hospital or Good Samaritan Hospital. Maternal medical data were extracted for three delivery cohorts established based on before (T1), during (T2), and after legalization (T3) of recreational marijuana and legalized availability. Univariate and multivariate models were created to study marijuana exposure on infants' birth weight. Results Marijuana exposure increased the risk of low birth weight (LBW; odds ratio [OR] = 1.42, 95% confidence interval [CI]: 1.01–2.01). This was more pronounced in full-term babies (OR = 1.72, 95% CI: 1.10–2.69), and was independently associated with a higher risk for small for gestational age (SGA; OR = 1.51, 95% CI: 1.49–1.53). The associations between marijuana exposure and SGA were maintained in cohort-specific models (OR = 1.53, 95% CI: 1.01–2.32 for T2, and OR = 1.43, 95% CI: 1.01–2.02 for T3, respectively). Conclusion Marijuana exposure verified by UDS was associated with LBW and SGA. However, recreational marijuana legalization and availability did not have direct impact on newborns' risk of LBW or SGA.

Birth Outcomes of Neonates Exposed to Marijuana in Utero

“…Risk of low birth weight was significantly increased among pregnant women who were exposed vs women who were not exposed to marijuana (RR, 2.06 [95% CI, 1.25 to 3.42]; P = .005), but the results were heterogeneous (τ 2 = 0.49; χ 2 7 = 230.25; P <.001; I 2 = 97.0%) ( Figure 2 A). 24 , 25 , 29 , 30 , 32 , 34 , 36 We could not solve the heterogeneity. When considering a diagnosis of small for gestational age, (defined <fifth percentile by birth weight), 6 studies 20 , 21 , 25 , 31 , 34 , 35 had enough data to be included, with a total of 22 928 patients.…”

“…After full-text screening, 16 studies, encompassing 59 138 patients, were ultimately included. 20 , 21 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 Figure 1 shows the flowchart of this workflow.…”

“…Details about included studies’ summaries and baseline characteristics are presented in Table 1 and Table 2 and eTable 1 in the Supplement . 20 , 21 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 Analyzed studies included 14 studies conducted in the United States, 20 , 21 , 24 , 25 , 26 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 1 study conducted in Canada, 27 and 1 study conducted in Jamaica. 28 Study group sizes ranged from 30 individuals who used marijuana vs 25 individuals who did not in Hayes et al 28 to 11 178 individuals with no marijuana use vs 1245 individuals who used marijuana in Linn et al 29 ( Table 1 and Table 2 ).…”

“…There was a significantly increased risk of small for gestational age among pregnant women exposed to marijuana compared with pregnant women who were not exposed (RR, 1.61 [95% CI, 1.44 to 1.79]; P < .001), and the results were homogenous (χ 2 5 = 1.56; P = .91; I 2 = 0%) ( Figure 2 B). 20 , 21 , 25 , 31 , 34 , 35 When comparing actual birth weight in grams, 10 studies 20 , 21 , 24 , 26 , 27 , 28 , 30 , 34 , 36 , 37 had enough data for inclusion, with a total of 18 405 patients. Fetal weight was significantly increased among pregnant women who were not exposed compared with pregnant women exposed to marijuana (mean difference, −112.30 [95% CI, −167.19 to −57.41] g; P < .001).…”

“…The results, however, were heterogeneous (τ 2 = 4673.87; χ 2 9 = 30.18; P < .001; I 2 = 70.0%) and we could not solve the heterogeneity ( Figure 3 A). 20 , 21 , 24 , 25 , 27 , 28 , 30 , 34 , 36 , 37 There were 3 studies 20 , 21 , 37 with enough data to compare neonatal head circumference, with a total of 2425 patients. Neonatal head circumference was significantly increased among pregnant women who were not exposed compared with pregnant women exposed to marijuana (mean difference, −0.52 [95% CI, −0.95 to −0.09] cm; P = .02).…”