Associations between pregnancy glucose measurements and risk of preterm birth: a retrospective cohort study of commercially insured women in the United States from 2003-2021.

PURPOSE: To investigate associations between glucose measurements during pregnancy and risk of preterm birth (PTB).

METHODS: Retrospective cohort study of commercially insured women with singleton live births in the United States from 2003-2021 using longitudinal medical claims, socioeconomic data, and eight glucose results from different types of fasting and post-load tests performed between 24-28 weeks of gestation for gestational diabetes screening. Risk ratios of PTB (<37 weeks) were estimated via Poisson regression for z-standardized glucose measures. Non-linear relationships for continuous glucose measures were examined via generalized additive models.

RESULTS: Elevations in all eight glucose measures were associated with increased risk (adjusted risk ratio point estimates: 1.05-1.19) of PTB for 196,377 women with non-fasting 50-gram glucose challenge test (one glucose result), 31,522 women with complete 100-gram, 3-hour fasting oral glucose tolerance test (OGTT) results (four glucose results), and 10,978 women with complete 75-gram, 2-hour fasting OGTT results (three glucose results). Associations were consistent after adjusting for and stratifying by sociodemographic and clinical factors. Substantial non-linear relationships (U-, J-, and S-shaped) were observed between several glucose measurements and PTB.

CONCLUSIONS: Elevations in various glucose measures were linearly and non-linearly associated with increased risk of PTB, even before diagnostic thresholds for gestational diabetes.