Postpartum depression is defined as minor or major depression occurring in the year following childbirth. Its prevalence is estimated to be between 10 and 15% in mothers and between 8 and 10% in fathers. It can have short and long term consequences on the health and well-being of the parent concerned but also on child development and on the couple’s and the family’s functioning. There is substantial literature on maternal postpartum depression. However paternal postpartum depression and joint parental postpartum depression have been less studied, in particular in a French context. A disadvantaged socioeconomic position is associated with an increased likelihood of postpartum depression and barriers to accessing prevention and treatment options. The underlying mechanisms of social inequality in parental postpartum depression are currently understudied. Social support during pregnancy, which appears to be a protective factor in maternal and paternal postpartum depression, is a candidate mechanism which can be targeted with interventions as early as at the beginning of pregnancy. The first objective of this thesis was to study the association between social support during pregnancy and joint parental postpartum depression, using data from the ELFE cohort study. Two dimensions of prenatal social support were identified: perceived versus received social support and informal versus formal social support. Next, associations between different aspects of social support during pregnancy and joint parental postpartum depression were estimated using multinomial regression models. This analysis showed that partner support during pregnancy was a protective factor against maternal, paternal and joint parental postpartum depression. The second objective of this thesis was to assess the role of different aspects of social support during pregnancy in social inequalities with regard to maternal postpartum depression, according to maternal migrant status, using multiple mediation analyses and data from the ELFE cohort study. Fathers were omitted from this second objective due to data-related limitations. Partner support during pregnancy mediates social inequalities with regard to maternal postpartum depression in nonmigrant women and in immigrant women. Further research and interventions on the role of informal and formal social support during pregnancy in social inequalities with regard to postpartum depression, taking into account parents’ social and socioeconomic characteristics are needed to improve prevention, especially in mothers and fathers at high risk of postpartum depression.