Any birth that occurs before 37 completed weeks of pregnancy is considered preterm, according to the study. Preterm births are the leading cause of infant mortality, but more and more preterm babies are surviving, the study authors noted. Yet, little information is available on what happens as these babies reach adulthood, they added.
The current finding comes from a Swedish study of al;most 675,000 people born between 1973 and 1979. Of these, nearly 28,000 were born preterm. The study followed the babies through 2008, when they were between 29 and 36 years old.
A total of 7,095 deaths occurred in the entire group. The researchers found a strong inverse association between each week of pregnancy and the risk of death for two age groups: children between 1 and 5 years old, and young adults (aged 18 to 36 years). No association was found between risk of death and the number of weeks of pregnancy for children between the ages of 6 and 17 years.
For the younger group, each additional week of pregnancy was associated with an 8 percent decreased risk of dying. For the young adults, that number was 4 percent for each additional week of pregnancy.
The incidence of death for young adults was 0.94 per 1,000 person-years for babies born between 22 and 27 weeks' gestation. For babies born between 28 and 33 weeks' gestation, the rate was 0.86 per 1,000 person-years. At 34 to 36 weeks' gestation, the rate was 0.65 and at normal gestation (37 to 42 weeks), the rate was 0.46 per 1,000 person-years, according to the study.
The researchers don't know exactly why there's an increased risk of death in adulthood, after a relatively long period where death risk isn't increased. "There is an increased risk of health problems in premature infants. Maybe some of these conditions have a long latency or period of development," suggested Crump.
Bromberg also noted that some of the life-saving interventions done to premat
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