Cytomegalovirus (CMV) subunit vaccine candidates include glycoprotein B (gB), and phosphoprotein ppUL83 (pp65). Using a guinea pig cytomegalovirus (GPCMV) model, this study compared immunogenicity, pregnancy outcome, and congenital viral infection following pre-pregnancy immunization with a three-dose series of modified vaccinia virus Ankara (MVA)- vectored vaccines consisting either of gB administered alone, or simultaneously with a pp65 homolog (GP83)-expressing vaccine. Vaccinated and control dams were challenged at midgestation with salivary gland-adapted GPCMV. Comparisons included ELISA and neutralizing antibody responses, maternal viral load, pup mortality, and congenital infection rates. Strikingly, ELISA and neutralization titers were significantly lower in the gB/GP83 combined vaccine group than in the gB group. However, both vaccines protected against pup mortality (60.5% in controls vs. 11.4% and 8.3% in gB and gB/GP83 combination groups, respectively; p<0.0001). Reductions in pup viral load were noted for both groups compared to control, but preconception vaccine resulted in a significant reduction in GPCMV transmission in the monovalent gB group only (26/44, 59 % v. 27/34, 79 % in controls; p<0.05). We conclude that, in the MVA platform, adding GP83 to a gB subunit vaccine interferes with antibody responses and diminishes protection against congenital GPCMV infection, but does not decrease protection against pup mortality.