•Pregnant women with ‘low’ omega-3 blood levels have higher risk for early preterm birth.•DHA supplementation during pregnancy can reduce premature birth rates in higher risk individuals.•There is no agreed upon blood DHA level that would define what ‘low’ omega-3 status is.•Blood DHA levels from 6 pregnancy studies were converted to a common DHA metric for comparison.•Having a standardized metric for ‘low’ DHA status is needed for use in clinical practice. Recent trials in pregnant women on the effects of supplemental DHA on early preterm birth (ePTB) risk have shown that there is a maternal blood docosahexaenoic acid (DHA) level below which risk for ePTB was increased and supplemental DHA was effective at reducing risk. However, DHA levels were expressed in different terms across these trials making cross study comparisons impossible. The purposes of this study were 1) to report interlaboratory conversion factors from study-specific metrics to a common metric, red blood cell (RBC) DHA measured by OmegaQuant Analytics (OQA), and 2) to translate reported pre- and post-treatment DHA levels from these trials into a RBC DHA for comparison. Data from five published and one unpublished study are included. Across these studies, the effects on RBC DHA levels after supplementation with 0, 200, 600, 800 and 1000 mg of DHA were (as a% change from baseline): 0 mg, no change; 200 mg, 15–20% increase; 600 mg, 55–60% increase; 800 mg, 13–65% increase; and 1000 mg, 51% increase. Standardization of fatty acid analysis and reporting and a target omega-3 or DHA level for identifying those for which higher dose DHA supplementation is indicated to prevent ePTB are needed for clinical use.