2.5. Supplement Database
We created a database that contains label information for each supplement reported. There were 472 unique supplements. Ninety-four did not contain nutrients of interest, e.g., amino acids, fiber, probiotics, and botanicals. Another 24 supplements included a nutrient of interest, but there was missing information on participant intake. The remaining 354 were included in our analyses. All supplements were categorized by the investigators based on the content, name, and primary purpose (for example, a fish oil supplement containing vitamin E was categorized in the category omega-3 fatty acid).Of the 354 supplements analyzed, only 136 met the definition of a prenatal multivitamin–mineral supplement, i.e., containing ≥3 vitamins + ≥1 mineral and specifically marketed for conception, prenatal, or postnatal use. This is the same definition used by Bailey et al. [Three sources of supplement label information were used to determine nutrient content: The Dietary Supplement Label Database (DSLD), 6 the Supplement Online Wellness Library (OWL) [Supplemental folate and folic acid were interpreted as 1 μg = 1 μg, despite known differences in bioavailability. Both the DHQ-II and NDSR provide the output of folate intake as dietary folate equivalents (DFE), accounting for differences in the bioavailability of folate consumed as naturally occurring food folate compared to synthetic folic acid added to fortified foods. Most supplements contain the synthetic form of folate, folic acid, while some prenatal vitamins do include at least a portion of the supplemental folate as the natural, active form 5-methyltetrahydrofolate. Many supplements contain a combination of preformed vitamin A or provitamin A carotenoids in varying proportions, which is not always reported on the supplement label. Supplemental vitamin A intake was also interpreted as 1 IU preformed vitamin A = 1 IU provitamin A carotenoids, despite differences in bioavailability. It was then converted to retinol activity equivalents (mcg RAE) using the conversion factor 1 IU = 0.3 mcg RAE [