Four fetal SNP alleles with the strongest univariate associations: paternally-transmitted IGF2 rs10770125 (P-value=2×10<sup>-4</sup>) and INS rs2585 (P-value=7×10<sup>-4</sup>), and maternally-transmitted KCNQ1(OT1) rs231841 (P-value=1×10<sup>-3</sup>) and KCNQ1(OT1) rs7929804 (P-value=4×10<sup>-3</sup>), were used to construct a composite fetal imprinted gene allele score which was associated with maternal glucose concentrations (P-value=4.3×10<sup>-6</sup>, n=981, r<sup>2</sup>=2.0%) and GDM prevalence (odds ratio per allele 1.44 (1.15, 1.80), P-value=1×10<sup>-3</sup>, n=89 cases and 899 controls).