SIDS Program Manual SIDS & Infant Death Program Manual and Trainer's Guide Trainer's Guide

What is SIDS?

Non-Modifiable Risk Factors


SIDS Age Range

The distribution of age at death has been a consistent epidemiologic feature of SIDS cases. The risk of SIDS peaks at 2 to 4 months of age. SIDS is rare during the first month of life and after the age of 6 months. About 90 percent of SIDS cases occur in infants less than 6 months old.53

Research has focused on pathophysiological features specific to infants in the 1- to 6-month age distribution in understanding the interaction between age distribution and SIDS. As discussed in the Triple Risk theory, the 2- to 4-month period is a critical development period for infants. Due to the vast amount of growth and changes infants encounter in this time frame, physiologically they are considered unstable and less able to react to environmental stressors.

A current and emerging issue related to age distribution is bedsharing. Studies of parentinfant bedsharing have been found to be strongly associated with a younger age at death, independent of any other factors.54,55 Other studies have found bedsharing to be a risk factor for infants less than six months of age, but the prone position as a risk factor for all age groups.56


Studies have consistently reported a higher ratio of male to female infants who die of SIDS (60 males : 40 females) independent of any other risk factor. Currently, there is further research to gain a greater understanding of exactly why this is the case by examining differences in X and Y chromosomes and hormonal levels between the genders.