Birth less than 37 weeks after conception. Infants born as early as 23–24 weeks may survive but many face lifelong disabilities (e.g., cerebral palsy, blindness, deafness). Premature infants account for 8–9percnt of live births but two-thirds of infant deaths. 40–50percnt of cases have no explanation; other cases can be attributed to such causes as maternal hypertension or diabetes, multiple pregnancy, or placental separation. With good care, about 85percnt of live-born premature infants should survive. Infants born very early (before 32–34 weeks) lack fully developed lungs and often develop respiratory distress syndrome. They also have problems maintaining body temperature and fighting infection. Most deaths result from breathing problems, infections, and brain or lung hemorrhages. Premature infants are characterized by low birth weight, small size, irregular breathing, absence of subcutaneous fat, and thin skin.
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Disorder with characteristics of premature aging. Affected persons have thin skin, go bald or gray early, and develop diseases of aging decades earlier than normal individuals. Not all systems are affected; there is no senility, no aging in the central nervous system. There are two major types. In the extremely rare Hutchinson-Gilford syndrome, children look 60 years old by age 10 and die at an average age of 13. The unrelated Werner syndrome is a recessive hereditary disease that begins in young adulthood and makes patients look 30 years older than they are; their average life span is 47 years.
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