While dietary guidelines about intake of specific nutrients in pregnant women are well-established, surprisingly little is known about dietary eating patterns or nutritional risk factors for SPTB.

In data from two large nationally-representative European studies, SPTB was predicted by a western diet, a finding confirmed by a smaller cohort in Australia. In a small cohort in Poland, intake of short- and medium-chain fatty acids was lower in women who had SPTB, and the placental-fetal transport of fatty acids was significantly different in SPTB cases. Furthermore, more than a single serving daily of either artificially-sweetened or sugar-sweetened beverages was also linked to SPTB. Low blood biomarker levels of antioxidant nutrients (ascorbic, vitamin E)7 and nutrients with an established anti-inflammatory role in health (omega 3 fatty acids,8 vitamin D9-11) have been suggested as potential nutrient modulators of SPTB. While these are very interesting findings, they do not explain whether these food patterns prevail in an urban U.S. population or why SPTB occurs. Furthermore, none of these potentially modifiable diet associations has been examined in the context of the entire series of physiological systems operating during pregnancy, namely diet, the gut microbiome, maternal plasma metabolome, placenta, and cord blood.

There is biological rationale to assume that dietary components could modify the gut microbiome and the maternal plasma metabolome during pregnancy. Artificial sweeteners induce glucose intolerance through an alternation in the gut microbiota. Chronic ingestion of sugar-sweetened beverages also results in similar plasma metabolic abnormalities (gut microbiome measures were not reported). In animal models of high fat diet feeding (similar to western diet), addition of N3FA ameliorated the gut dysbiosis and reduced endotoxin production. Furthermore, in healthy volunteers, the investigators have recently linked typical dietary intake patterns with the gut microbiome. Dietary patterns of high protein and animal fat intake were predominantly associated with Bacteroides enterotypes, while carbohydrate intake was associated with Prevotella. While the microbiome composition changes rapidly after change in diet, the enterotype identity is resilient over time. The investigators followed these findings with another study comparing the extreme diets of vegans (no animal products) to the more typical mixed western diet pattern of omnivores, and extended the analytical approaches to include assessment of the plasma metabolome. By observing the microbiome and metabolome, the investigators were clearly able to distinguish with 91% accuracy whether a subject was vegan or omnivore. Furthermore, the investigators could determine metabolomic characteristics that were contributed by gut bacterial metabolism, but only in subjects with high plant food intake. These findings in healthy volunteers raise the possibility that gut microbial populations could interact with maternal tissues or plasma to produce an inflammatory state that might result in preterm parturition. Indeed, the alteration of the gut microbiota observed in the third trimester of pregnancy and its effects on host metabolism are supportive of this notion.