Prenatal experience with infant- and child-directed speech (IDS/CDS) may affect newborns' speech perception. We examined this possibility using an existing neonatal database from a recent cross-language study (Moon, Lagercrantz, & Kuhl, 2011). Seventy-three American and Swedish neonates (Mage = 32.58 hr, SD = 13.58 hr) were retrospectively coded as either having High (n = 32) or Low (n = 41) prenatal IDS/CDS exposure based on whether there were any children younger than 4 years old in the household during pregnancy. We compared the mean sucks for contingent presentations of prototypes and nonprototypes of vowel stimuli (native or foreign) among groups. A mixed 3-way ANOVA revealed a significant interaction: Neonates responded to prototypes and nonprototypes differently in the High IDS/CDS group, whereas there was a lack of differential responses in the Low IDS/CDS group. Future research with well-controlled measurement of prenatal speech is warranted.