This systematic review of 58 observational studies identified hypothetical causal mechanisms explaining the effects of short and long intervals between pregnancies on maternal, perinatal, infant, and child health, and critically examined the scientific evidence for each causal mechanism hypothesized. The following hypothetical causal mechanisms for explaining the association between short intervals and adverse outcomes were identified: maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous cesarean delivery, and abnormal remodeling of endometrial blood vessels. Women's physiological regression is the only hypothetical causal mechanism that has been proposed to explain the association between long intervals and adverse outcomes. We found growing evidence supporting most of these hypotheses.

Voluntary family planning brings transformational benefits to women, families, communities, and countries. Investing in family planning is a development “best buy” that can accelerate achievement across the 5 Sustainable Development Goal themes of People, Planet, Prosperity, Peace, and Partnership.

In Latin America, interpregnancy intervals shorter than 12 months and longer than 59 months are independently associated with increased risk of adverse perinatal outcomes. These data suggest that spacing pregnancies appropriately could prevent perinatal deaths and other adverse perinatal outcomes in the developing world.

BackgroundShort birth intervals are associated with an increased risk of adverse perinatal outcomes. However, reduction of rates of short birth intervals is challenging in low-resource settings where majority of the women deliver at home with limited access to family planning services immediately after delivery. This study examines the feasibility of integrating a post-partum family planning intervention package within a community-based maternal and newborn health intervention package, and evaluates the impact of integration on reduction of rates of short birth intervals and preterm births.MethodsIn a quasi-experimental trial design, unions with an average population of about 25 000 and a first level health facility were allocated to an intervention arm (n = 4) to receive integrated post-partum family planning and maternal and newborn health (PPFP-MNH) interventions, or to a control arm (n = 4) to receive the MNH interventions only. Trained community health workers were the primary outreach service providers in both study arms. The primary outcomes of interest were birth spacing and preterm births. We also examined if there were any unintended consequences of integration.ResultsAt baseline, short birth intervals of less than 24 months and preterm birth rates were similar among women in the intervention and control arms. Integrating PPFP into the MNH intervention package did not negatively influence maternal and neonatal outcomes; during the intervention period, there was no difference in community health workers’ home visit coverage or neonatal care practices between the two study arms. Compared to the control arm, women in the intervention arm had a 19% lower risk of short birth interval (adjusted relative risk (RR) = 0.81, 95% confidence interval (CI) = 0.69-0.95) and 21% lower risk of preterm birth (adjusted RR = 0.79; 95% CI = 0.63-0.99).ConclusionsStudy findings demonstrate the feasibility and effectiveness of integrating PPFP interventions into a community based MNH intervention package. Thus, MNH programs should consider systematically integrating PPFP as a service component to improve pregnancy spacing and reduce the risk of preterm birth.

Evidence shows that effective prevention of rapid repeat pregnancy among adolescents links adolescent-friendly clinical contraceptive services with non-clinical interventions that contribute to positive youth development.