interbirthinterval

Interbirth interval (IBI), also called birth interval, is the period between two consecutive live births for the same mother. It is typically measured in months from the date of one birth to the date of the next birth. In population-health analysis, the interbirth interval is the interval between births, though some discussions distinguish it from the interpregnancy interval, which measures time from the end of one pregnancy to conception of the next.

Evidence links short interbirth intervals with higher risks of adverse outcomes for both mother and child. Short intervals—commonly defined as less than 18 to 24 months between births—are associated with increased chances of preterm birth, low birth weight, and infant mortality, as well as maternal complications such as postpartum anemia and infections. Longer intervals do not consistently show the same pattern and may reflect other factors such as maternal age or health status. Lactational amenorrhea from breastfeeding and access to effective contraception are among the factors that influence interval length.

Determinants of interbirth intervals include biological, behavioral, and sociocultural factors. Breastfeeding duration, postpartum contraception availability, education, income, and cultural norms all help shape how soon a mother has another child. Data on birth intervals rely on birth histories collected in surveys and administrative records, which can be affected by recall and reporting biases.

Public health relevance centers on family planning and maternal–child health. Many guidelines advise aiming for a spacing of at least 18 to 24 months after a live birth to reduce risks. Programs that expand access to contraception, promote maternal health, and support informed reproductive choices can influence interbirth intervals and associated outcomes.