Cannabis use among pregnant people is on the rise. This trend is likely to be continue, especially among people who are younger or those live in states where cannabis is legal. Yet, pregnant people may not be aware of the potential risks. Prenatal exposure to cannabis has been consistently linked to low birth weight. Our pilot data further suggests that prenatal exposure to cannabis is associated with rapid growth in the first three years of life followed by increased adiposity and glucose at age 5 years. However, important gaps in knowledge remain. It is unclear whether a particular cannabinoid may be driving this association, as epidemiologic studies have examined the independent or joint effects of delta 9-tetrahydrocannabinol (Δ9- THC) and cannabidiol (CBD). Additionally, there is a need to identify protective factors that mitigate risk, given that this exposure may have occurred in the past. Furthermore, it is unknown whether there are developmental windows in which the offspring may be more susceptible to these cannabinoids. In response to NOT-DA-22- 003, our overarching goal is to determine when and how prenatal exposure to cannabis impacts childhood adiposity and cardiometabolic health. These specific health traits are relevant to adult health as they track across the lifespan and have been previously collected in our rich Colorado-based cohort (Healthy Start; R01DK076648). Pregnant people were recruited between 2010 and 2014, amid state-wide legalization of cannabis for recreational use but prior to widespread health messaging about the potential harm to the fetus. We propose to measure Δ9-THC and CBD in maternal serum (collected at ~17 and ~27 weeks gestation) and in umbilical cord blood. Our central hypothesis is that prenatal exposure to cannabis will be associated with increased adiposity and altered cardiometabolic traits at age 5 years. In Aim 1, we will test the hypothesis that the associations between Δ9-THC/CBD and child health will be stronger among those with co-exposure to tobacco and mitigated by a longer duration of breastfeeding and higher intakes of key nutrients. In Aim 2, we will examine windows of susceptibility in which prenatal exposure to Δ9-THC and/or CBD influences growth and cardiometabolic health among the 5-year-old offspring. we will identify windows of heightened susceptibility. This exploratory study includes a well-characterized, observational cohort with a relatively high prevalence of exposure (13% at mid-gestation) and a novel on cardiometabolic outcomes, making it uniquely positioned to advance our understanding of when and how prenatal exposure to cannabis influences child health. Results may inform future targeted interventions to limit the effects of exposure during pregnancy.