Background <p>Interpregnancy interval (IPI) has been reported to be associated with the risk of pregnancy complications. Short IPIs have been associated with higher risks of preterm birth, small for gestational age, low birthweight, fetal growth restriction, and perinatal mortality. However, there is limited information on how these associations differ according to the developmental status of a country. This review is therefore designed to examine the impact of the developmental status of a country on the relationship between IPI and perinatal complications.</p> Methods <p>Studies will be identified through a comprehensive search of MEDLINE, EMBASE, Global Health, LILACS, and African Index Medicus databases, using key terms including “interpregnancy interval”, “birth interval”, “preterm birth”, “small for gestational age”, “fetal growth restriction”, and “perinatal mortality”. Studies to be included will be screened for data reporting on IPI and relevant outcomes. The study population will consist of women with two or more singleton births. The exposure of interest is short IPI, categorised as (1) &lt; 24&#xa0;monthsmonths; ≤ 18&#xa0;months; and ≤ 12&#xa0;months between the birth of a child and conception of the next pregnancy. These exposure groups will be compared against the World Health Organisation recommendation of an IPI of at least 24&#xa0;months. Co-primary outcomes are preterm birth, small for gestational age, fetal growth restriction, low birthweight, and perinatal mortality. The developmental status of study populations will be categorised according to the World Bank income-based country classifications for low-, middle-, and high-income countries. Studies will be included if they have an observational design and excluded if they are systematic reviews with no new data. All studies will be screened, data extracted, and bias assessed by two independent authors, with all discrepancies being resolved by consensus or the advice of a third author. If studies have a low heterogeneity (<i>I</i>² &lt; 50%), the Mantel–Haenszel method, with a fixed-effects model, will be used to calculate pooled odds ratios (ORs) with 95% confidence intervals. If studies have high heterogeneity (<i>I</i>²&#xa0;≥ 50%) a random-effects (inverse-variance) model will be used instead.</p> Discussion <p>Results from this review have the potential to guide future recommendations on optimal IPI in both high and low-resource countries. Further, they have the potential to assist in developing health strategies to target specific populations at risk from short IPI-related adverse pregnancy outcomes.</p> Systematic review registration <p>PROSPERO CRD420251075289.</p>