A method for assessing risk of preterm birth for a pregnant subject, the method comprising: (a) preparing a microparticle-enriched fraction from a sample from the pregnant subject, wherein the preparing step comprises_using size-exclusion chromatography with an agarose solid phase and an aqueous liquid phase; (b) detecting a level of two or more proteins in the fraction, wherein the two or more proteins are one or more proteins of the preterm group subset consisting of hemopexin, alpha-1B-glycoprotein (A1BG), serum albumin, apolipoprotein D (APOD), apolipoprotein L1 (APOL1), zinc-alpha-2-glycoprotein (AZGP1), Ig heavy chain mu 1 (IGHM1), IgM heavy chain mu 2 (IGHM2), and serotransferrin, wherein the protein or at least one of the proteins is HPX, and one or more proteins of the term group subset consisting of complement component 1r (Clr), complement component 3, complement component 4B (C4B), complement factor H, Ig heavy chain alpha 2 (IGHA2), and Ig kappa variablel-9 (IGKV1-9); and (c) determining that the pregnant subject is at an increased risk of preterm birth when the level of one or more proteins of the preterm birth group consisting of A1BG, ALB, APOD, APOL1, AZGP1, HPX, IGHM1, IGHM2, and TF is above a threshold level, and/or when the level of one or more of proteins of the term birth group consisting of C1R, C3, C4B, CFH, IGHA2, and IGKV1-9 is below a threshold level; or determining that the pregnant subject is not at an increased risk of preterm birth when the level of one or more proteins of the preterm birth group consisting of A1BG, ALB, APOD, APOL1, AZGP1, HPX, IGHM1, IGHM2 and TF, is below a threshold level, and/or when the level of one or more of proteins of the term birth group consisting of C1R, C3, C4B, CFH, IGHA2, IGKV1-9, is above a threshold level. (a) preparing a microparticle-enriched fraction from a sample from the pregnant subject, wherein the preparing step comprises_using size-exclusion chromatography with an agarose solid phase and an aqueous liquid phase; (b) detecting a level of two or more proteins in the fraction, wherein the two or more proteins are one or more proteins of the preterm group subset consisting of hemopexin, alpha-1B-glycoprotein (A1BG), serum albumin, apolipoprotein D (APOD), apolipoprotein L1 (APOL1), zinc-alpha-2-glycoprotein (AZGP1), Ig heavy chain mu 1 (IGHM1), IgM heavy chain mu 2 (IGHM2), and serotransferrin, wherein the protein or at least one of the proteins is HPX, and one or more proteins of the term group subset consisting of complement component 1r (Clr), complement component 3, complement component 4B (C4B), complement factor H, Ig heavy chain alpha 2 (IGHA2), and Ig kappa variablel-9 (IGKV1-9); and (c) determining that the pregnant subject is at an increased risk of preterm birth when the level of one or more proteins of the preterm birth group consisting of A1BG, ALB, APOD, APOL1, AZGP1, HPX, IGHM1, IGHM2, and TF is above a threshold level, and/or when the level of one or more of proteins of the term birth group consisting of C1R, C3, C4B, CFH, IGHA2, and IGKV1-9 is below a threshold level; or determining that the pregnant subject is not at an increased risk of preterm birth when the level of one or more proteins of the preterm birth group consisting of A1BG, ALB, APOD, APOL1, AZGP1, HPX, IGHM1, IGHM2 and TF, is below a threshold level, and/or when the level of one or more of proteins of the term birth group consisting of C1R, C3, C4B, CFH, IGHA2, IGKV1-9, is above a threshold level.