Objective  The aim of this study was to evaluate rates of preterm birth (PTB) and obstetric complication with maternal serum analytes > 2.5 multiples of the median (MoM) by degree of elevation. Study Design  Retrospective cohort study of singleton live-births participating in the California Prenatal Screening Program (2005-2011) examining PTB and obstetric complication for α-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin A (INH) by analyte subgroup (2.5 to < 6.0, 6.0 to < 10.0, and ≥ 10.0 MoM vs. < 2.5 MoM). Results  The risk of obstetric complication increased with increasing hCG, AFP, and INH MoM, and were greatest for AFP and INH of 6.0 to <10.0 MoM. The greatest risk of any adverse outcome was seen for hCG MoM ≥ 10.0, with relative risk (RR) of PTB < 34 weeks of 40.8 (95% confidence interval [CI]: 21.7-77.0) and 13.8 (95% CI: 8.2-23.1) for obstetric complication. Conclusions  In euploid, structurally normal fetuses, all analyte elevations > 2.5 MoM confer an increased risk of PTB and, except for uE3, obstetric complication, and risks for each are not uniformly linear. These data can help guide patient counseling and antenatal management.