Infant mortality research breakthrough

May 3, 1999

Short intervals between pregnancies have been linked to increased risk of infant mortality due to intentional and unintentional injuries and sudden infant death syndrome (SIDS), a team of researchers from the University of Chicago Children's Hospital reports May 3, 1999 at the annual meeting of Pediatric Academic Societies (the American Pediatric Society, the Society for Pediatric Research and the Ambulatory Pediatric Association) in San Francisco, California.

Using a 50 percent random sample of United States birth and death data from 1990 (1,824,606 births), researchers assessed the relationship between short (less than 12 months) interpregnancy intervals--the time between the birth of one child and the conception of another child--and cause-specific infant mortality rates.

The study looked at infant mortality due to 11 causes of death: maternal complications, complications of placenta, hypoxia/asphyxia, congenital anomalies, prematurity, respiratory distress syndrome, pneumonia, sudden infant death syndrome, infections, and unintentional and intentional injuries. In addition to pregnancy intervals and infant birth weight, factors such as maternal age, education, marital status, race/ethnicity, birth order, prenatal care, and tobacco and alcohol use were factored into the analysis.

Results showed that short interpregnancy intervals are associated with higher risks of infant mortality due to intentional and unintentional injuries and SIDS when controlling for sociodemographic factors and birthweight.

Intervals less than six months were associated with a three-fold increased risk in infant death due to intentional injuries, a 74 percent increased risk due to unintentional injuries, and a 55 percent increased risk due to SIDS.

In addition, a duration of less than six months between pregnancies was associated with a two-fold increased risk of infant mortality and a duration of six to 12 months between pregnancies was associated with a 39 percent increased risk of infant mortality when all causes were combined. Infant birth weight and sociodemographic characteristics of the mother played a large role in this increased risk of death.

There was no association between short intervals in pregnancy and the risk of death due to congenital anomalies, maternal complications, infections, hypoxia/asphyxia, and complications of placenta.

"This study shows that short intervals are associated with specific causes of death and underscores the importance of birth spacing for infant health," says Babak Khoshnood, MD, research associate in the department of pediatrics at the University of Chicago Children's Hospital. "The effect of short interval on infant mortality may just be the tip of the iceberg. Short intervals may also be related to maternal stress, parental attention toward the child, a child's developmental milestones, or the incidence of non-fatal accidents particularly since short birth spacing is more common in, and might be more taxing for disadvantaged families with fewer resources to care for their children."

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