Prenatal Cannabis Use and Neonatal Outcomes: What the Latest Research Reveals

Over the past two decades, the rate of cannabis use during pregnancy has more than doubled, making it the most commonly used federally illegal substance in pregnancy. As cannabis use becomes increasingly mainstream and the statistics of use from expectant mothers rise, a critical and complex question continues to spark debate: What are the potential effects of using cannabis during pregnancy on neonatal health? For some pregnant women, cannabis offers relief from nausea, anxiety, or chronic pain. However, growing scientific evidence warns that this choice may carry unintended risks for the developing fetus.

Key Findings: The Impact of Prenatal Cannabis

The study¹, Prenatal Cannabis Use and Neonatal Outcomes: A Systematic Review and Meta-Analysis, offers the most in-depth look at pregnancy and cannabis use to date. Drawing from data spanning more than 21 million pregnancies across 51 studies, this systematic review and meta-analysis provides insights into how prenatal cannabis exposure may impact four major neonatal outcomes.

After adjusting for confounding factors such as tobacco use, the researchers found that prenatal cannabis use was associated with increased risks for several adverse outcomes:

• Low Birth Weight (LBW)
• Preterm Birth (PTB)
• Small for Gestational Age (SGA)
• Perinatal Mortality

The strength of evidence was rated moderate for LBW, PTB, and SGA, and low for perinatal mortality. Additionally, a dose-response relationship was observed as heavier self-reported cannabis use was associated with even greater risks.

Interpreting the Findings: A Closer Look at the Limitations

While the findings raise concern, it is crucial to interpret them within the context of several significant limitations, which include:

Observational Data and Causality

All included studies were observational. Unlike randomized controlled trials (which are unethical in this context at current), observational studies cannot definitively establish cause and effect. Associations may be influenced by unmeasured or residual confounding variables.

Self-Reported Cannabis Use

Many studies relied on self-reported cannabis use, which is prone to underreporting due to stigma, fear of legal repercussions, or recall bias. This underestimation could skew exposure assessments. Furthermore, the expectant mother could underreport use of cofounding factors, including tobacco and alcohol.

Variability in Exposure Measurement

There was no consistent measurement of cannabis exposure across studies. Differences in frequency, dose, timing (e.g., first vs. third trimester), and potency were often not accounted for, making it difficult to determine dose-response relationships.

Confounding by Other Factors

Although the study adjusted for tobacco use, many other potential confounders—such as alcohol use, other drugs, socioeconomic status, environmental exposures, maternal diet, chronic stress, and access to prenatal care—were inconsistently measured or not controlled for. These factors independently affect neonatal outcomes and may partially or fully explain observed associations.

Study Heterogeneity

Differences in study design, populations, geographic regions, and outcome definitions introduce variability, limiting the precision and generalizability of pooled estimates.

Path Forward: The Need for Rigorous Research

Understanding the true impact of prenatal cannabis use requires accurate, reliable data. If confounding factors like nutrition, environmental toxins, maternal stress, and concurrent substance use are not fully accounted for, it becomes impossible to isolate the specific contribution of cannabis. For example, low-income individuals may experience higher stress, poorer diet, and greater exposure to pollutants—all of which can contribute to low birth weight or preterm birth, independent of cannabis use.

Without precise exposure measurements (e.g., biological verification via urine or blood tests), standardized definitions, and comprehensive adjustment for these confounders, current findings must be interpreted with caution. Misattributing risk solely to cannabis without considering broader maternal health factors risks oversimplifying an extremely complex issue.

To more accurately determine the risks associated with prenatal cannabis use, future studies must:

• Use biological markers to verify cannabis exposure and reduce reliance on self-reporting.
• Standardize exposure measurements (including dose, frequency, potency, and timing during pregnancy).
• Control for a broader range of confounders, such as maternal nutrition, environmental exposures, psychological stress, and other substance use.
• Employ prospective, longitudinal designs that follow individuals over time to establish temporal relationships.
• Conduct subgroup analyses to explore how effects may vary by demographic factors.

Final Thoughts

The systematic review highlights concerning associations between prenatal cannabis use and adverse neonatal outcomes. While these findings are important, they must be interpreted with caution due to several limitations, including reliance on observational studies, self-reported data, and incomplete control for potential confounding factors.

These challenges underscore the urgent need for more rigorous clinical research. Without well-designed, controlled studies, it is difficult to draw clear conclusions about the specific risk cannabis may pose during pregnancy. As a result, both patients and healthcare providers are left without the concrete, evidence-based guidance necessary to make fully informed decisions.

While healthcare providers should continue to advise caution regarding cannabis use during pregnancy, they also need to acknowledge the complexity of the existing evidence. At the same time, the research community must prioritize more accurate, controlled studies to better understand the specific risks and disentangle the effects of cannabis from other maternal and environmental factors.

Improving the quality and precision of research in this area is essential. By generating clearer, more definitive data, we can better understand the effects of cannabis on maternal and fetal health and offer guidance that is rooted in science. By advancing the quality and precision of research, we can move toward evidence-based guidance that protects maternal and child health.

Studies Referenced:

^{1. Lo JO, Ayers CK, Yeddala S, et al. Prenatal Cannabis Use and Neonatal Outcomes: A Systematic Review and Meta-Analysis. JAMA Pediatr. Published online May 05, 2025. doi:10.1001/jamapediatrics.2025.0689}