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Related to neonatal period: Perinatal period
the interval from birth to 28 days of age. It represents the time of the greatest risk to the infant. Approximately 65% of all deaths that occur in the first year of life happen during this 4-week period.
ne·o·na·tal pe·ri·od(nē'ō-nā'tăl pēr'ē-ŏd)
The time elapsed between birth and 28 days of age. The first 24 hours of life are the most vulnerable time for the neonate because major physiologic adjustments are needed for extrauterine life.