Objective
To investigate oxidative stress as a mechanism of preterm birth in human subjects, we examined associations between urinary biomarkers of oxidative stress measured at multiple time points during pregnancy and preterm birth.
Study Design
This nested case-control study included 130 mothers who delivered preterm and 352 who delivered term who were originally recruited as part of an ongoing prospective birth cohort at Brigham and Women’s Hospital. Two biomarkers, including 8-hydroxydeoxyguanosine (8-OHdG) and 8-isoprostane were measured in urine samples collected at up to four time points (median 10, 18, 26, and 35 weeks) during gestation.
Results
Urinary concentrations of 8-isoprostane and 8-OHdG decreased and increased, respectively, as pregnancy progressed. Average levels of 8-isoprostane across pregnancy were associated with increased odds of spontaneous preterm birth (adjusted odds ratio [aOR]=6.25, 95% confidence interval [CI]=2.86, 13.7), and associations were strongest with levels measured later in pregnancy. Average levels of 8-OHdG were protective against overall preterm birth (aOR=0.19, 95%CI=0.10, 0.34), and there were no apparent differences in the protective effect in cases of spontaneous preterm birth compared to cases of placental origin. Odds ratios for overall preterm birth were more protective in association with urinary 8-OHdG concentrations measured early in pregnancy.
Conclusions
Maternal oxidative stress may be an important contributor to preterm birth, regardless of subtype and timing of exposure during pregnancy. The two biomarkers measured in the present study had opposite associations with preterm birth; an improved understanding of what each represents may help to more precisely identify important mechanisms in the pathway to preterm birth.