Cannabis Use During Pregnancy Was Associated with More Than Double the Risk of Stillbirth | Research

The takeaway

A large case-control study found cannabis was the most common illicit drug detected in stillbirth cases, with a positive cord test associated with 2.3 times the odds of stillbirth.

Read this if you are pregnant or planning pregnancy and want to understand substance use risks.

Cannabis-positive cord test: 2.34x odds of stillbirth (partially confounded by smoking)

What the researchers found

Among 663 stillbirth deliveries and 1,932 live birth controls, a positive umbilical cord test for any illicit drug was associated with stillbirth (OR 1.94). Cannabis was the most commonly detected drug, and its positive cord test was associated with 2.34 times the odds of stillbirth (95% CI: 1.13-4.81), though this effect was partially confounded by smoking.

Both self-reported smoking and objective cotinine levels showed a dose-response relationship with stillbirth risk. Even apparent passive smoke exposure (positive cotinine but no reported smoking history) was associated with doubled stillbirth odds (OR 2.06, 95% CI: 1.24-3.41).

Cannabis use, smoking, illicit drug use, and secondhand smoke exposure, either separately or in combination, were all associated with increased stillbirth risk.

Why it matters

This is among the largest and most rigorously designed studies examining cannabis and stillbirth risk. The use of objective cord testing (rather than relying solely on self-report) strengthens the findings. As cannabis legalization expands, the relevance of these findings may increase.

The numbers in context

663 stillbirths and 1,932 live births. Cannabis cord test: OR 2.34 (95% CI: 1.13-4.81). Any illicit drug: OR 1.94. Passive smoke: OR 2.06. Smoking showed dose-response relationship.

How the study worked

The Stillbirth Collaborative Research Network conducted a case-control study from March 2006 to September 2008, covering over 90% of deliveries in five geographically diverse U.S. regions. Umbilical cord homogenate was tested for illicit drugs and maternal serum was analyzed for cotinine (a smoking biomarker). Objective biological measures supplemented self-reported data.

What this study cannot tell us

The cannabis association was partially confounded by smoking, making it difficult to isolate the independent effect of cannabis. Not all cases had cord homogenate available (63% of stillbirths, 54% of controls). A positive cord test indicates exposure but does not quantify the amount or timing of use. The study cannot determine if cannabis was causally related to stillbirth or a marker for other risk factors.

How to read the evidence

This is a large, multicenter case-control study using objective biological measures, providing strong evidence for the association.

When this study was published

Published in 2014. Research on cannabis use during pregnancy and birth outcomes has expanded substantially since.

The bigger picture

Stillbirth affects approximately 1 in 160 pregnancies in the U.S. and its causes are often unclear. This study identifies modifiable risk factors, particularly cannabis and smoking, that could be targeted through prenatal counseling and cessation support.

Questions still open

What is the independent effect of cannabis after fully controlling for smoking? Is there a dose-response relationship for cannabis and stillbirth? What biological mechanism could link cannabis to stillbirth?

Common questions

Does this prove cannabis causes stillbirth?

The study found an association but cannot prove causation. The cannabis effect was partially confounded by smoking, meaning some of the risk may be due to co-occurring tobacco use. However, the association remained significant even after adjustment.

What is cord homogenate testing?

Umbilical cord tissue is homogenized and tested for drug metabolites. This provides an objective measure of fetal drug exposure that is not dependent on maternal self-report and can detect use over a longer window than urine or blood testing.

Read the original research

Association between stillbirth and illicit drug use and smoking during pregnancy.

Obstetrics and gynecology, 123(1), 113-125

View on PubMed ↗Publisher’s paper ↗

Citation

Varner, Michael W; Silver, Robert M; Rowland Hogue, Carol J; Willinger, Marian; Parker, Corette B; Thorsten, Vanessa R; Goldenberg, Robert L; Saade, George R; Dudley, Donald J; Coustan, Donald; Stoll, Barbara; Bukowski, Radek; Koch, Matthew A; Conway, Deborah; Pinar, Halit; Reddy, Uma M. (2014). Association between stillbirth and illicit drug use and smoking during pregnancy.. Obstetrics and gynecology, 123(1), 113-125. https://doi.org/10.1097/AOG.0000000000000052