The present study aimed to better understand the contribution of multiculturalism on coparenting dynamics during the transition to parenthood. In order to measure the extent of couples' multiculturalism, the Couple Diversity Index (CDI) was created. This measure considers different parameters as partners' differences of nationality, country of birth, continent of birth, country of compulsory education, mother tongue and religion. Coparenting dynamics were investigated through a couple's discussion-task during the prenatal period and the Lausanne Trilogue Play paradigm during the prenatal and postnatal period. The quantitative analyses results did not show any statistically significant relation between the CDI and coparenting dynamics both during the prenatal and postnatal period. Qualitative analyses revealed that all couples, regardless of the couple's multiculturalism, have to face and negotiate questions tied to the transmission of family and group affiliation values to their child. The specificity of multicultural couples appeared when negotiating one or more cultural identity markers for the child. Thus, the results showed that a multicultural family's identity is already being shaped during pregnancy.