Preferred and Actual Interbirth Intervals in Women with Multiple-Partner Fertility

Objective: Mothers with multiple-partner fertility have longer interbirth intervals (IBI) than mothers with single-partner fertility, suggesting that partner change makes it harder to achieve preferred birth spacing and family planning. Previous studies have, however, overlooked possible differences in preferred IBI length. Here, we investigated how partner change between the first and second child moderates the association between preferred and actual IBI. Methods: We used retrospective self-report survey data from 728 mothers living in Finland with at least two children. Results: Mothers with multiple-partner fertility had longer actual IBIs (35 months) than mothers with single-partner fertility (89 months). We found a weaker association between preferred and actual IBI length in mothers with multiple-partner fertility compared to mothers with single-partner fertility when controlling for maternal age, miscarriages, abortions, and in-vitro fertilization. Conclusions: Our findings support the notion that multiple-partner fertility makes it harder for mothers to achieve their preferred birth spacing, as partner change is associated with considerably longer IBIs. The increased discrepancy in preferred and actual IBIs in mothers with multiple-partner fertility should be considered both in family planning and future studies.