Researchers have examined the contribution of women’s age at first pregnancy to the prediction of union quality across the transition to motherhood, but the emerging picture is inconsistent. The authors investigated the moderator role of union length in the relationship between the 2 variables. A sample of 143 Canadian women completed the Dyadic Adjustment Scale during pregnancy and at 6 months postpartum. As predicted, after partialing out the influence of other demographic variables, union length moderated the relationship between maternal age and changes in union quality across the transition, p < .001. The results showed that postponing motherhood to a later age has positive effects on women’s union quality only among those who are in long-term relationships.