Human birth weight is under stabilizing selection, seeking balance between extremes of high and low, thereby reducing fetal and maternal perinatal mortality risk. Certain combinations of maternal killer immunoglobulin-like receptor () and paternally derived fetal human leuokocyte antigen-C () alleles were previously associated with higher risk of high and low birth weight in a study with limited sample size (n=1,316). Using recently developed methods to impute and haplotypes using single nucleotide polymorphism (SNP) genotype data, we tested associations of fetal and maternal genotypes with offspring birth weight in a large sample. We imputed haplotypes using the KIR*IMP imputation software in 10,602 mother-offspring pairs of European descent from singleton pregnancies from five studies. Using mixed linear regression models to account for mothers with multiple children, we tested associations between maternal vs haplotypes (, genotypes) as well as copy number of activating receptor gene (0, 1, 2 copies of the gene) in the presence of fetal alleles, and offspring birth weight. Associations were analyzed in each cohort before performing a meta-analysis to estimate the interaction effects between maternal and fetal on birth weight across the entire sample. The haplotypes achieved imputation accuracy estimated at >95% in most of the cohorts. No interaction effects were observed between either the maternal vs. haplotype or the maternal locus and fetal . When specifically trying to replicate the previously associated combination of maternal and paternally inherited fetal , there was a negligible change in offspring birth weight for each additional allele and of paternal origin (7g lower birth weight per allele [95% CI: -54, 40], = 0.78). We found little evidence of association between birth weight and maternal haplotypes or fetal and were unable to replicate previously reported findings. Our observations reinforce the importance of replication and the use of large sample sizes in the validation of genetic associations.