Persistent racial disparities in low birth weight (LBW) in the United States may be better understood through the adoption of a life course perspective that considers differential exposure and vulnerability of Black and White women to socioeconomic position across generations. Using a multigenerational dataset of singleton birth certificates from South Carolina from 1989 to 2020 linked along the maternal line, we constructed intergenerational social mobility trajectories of grandmaternal and maternal education and compared unadjusted and adjusted associations between trajectories and LBW among Black and White women. We found that White women were more likely to be upwardly mobile, and Black women to be downwardly mobile. We found a protective association between upward mobility and LBW for all White women, but only for the most highly educated Black women, consistent with the theory of marginalization-related diminished returns. We also observed a difference by race in the association between downward mobility and LBW, such that high childhood socioeconomic position better buffered low adulthood socioeconomic position for White women than Black women, consistent with theories of compensatory advantage. Finally, we observed racial disparities in the prevalence of LBW even at the highest levels of maternal education, highlighting the inability of even high socioeconomic position across two generations to reduce Black/White disparities in LBW.