From pregnancy to 36 months postpartum , mothers in the intervention group had significantly greater parenting knowledge ( effect size = 0.42 ) and parental locus of control ( effect size = 0.17 ) , fewer depressive symptoms ( effect size = 0.16 ) and externalizing problems ( effect size = 0.14 ) , and lower past month use of marijuana ( odds ratio = 0.65 ) and illegal drugs ( odds ratio = 0.67 ) .