Interbirth

Interbirth refers to the period between two successive births. In demographic and health contexts, it is commonly called the interbirth interval (IBI) and is measured from the date of one live birth to the date of the next. IBI is used to study fertility patterns, maternal health, and child outcomes.

Typical values and guidelines vary by population, but many studies show a median interbirth interval of about two to three years in various settings. Health organizations often emphasize a minimum spacing of 24 months after a live birth before attempting another pregnancy, to reduce risks of adverse outcomes for both mother and baby.

Biological factors influence interbirth intervals. The postpartum period involves uterine involution and the recovery of maternal energy stores. Lactation can suppress ovulation through lactational amenorrhea, contributing to natural, temporary spacing between pregnancies.

Health implications of interbirth interval length are mixed. Short intervals (for example, less than 18 to 24 months) have been linked with higher risks of preterm birth, low birth weight, and small-for-gestational-age infants, as well as maternal complications such as anemia and nutrient depletion. Longer intervals may reflect infertility or age-related factors and can be associated with different health risks.

Determinants of birth spacing include fertility, access to contraception, cultural norms, education, socioeconomic status, and health policies. Variation in interbirth intervals exists across regions and over time, influenced by both biological factors and social determinants.

Measurement typically relies on birth histories from surveys or vital records, with IBI expressed in months or years and sometimes categorized for analytical purposes.