Compared with full-term babies, preterm infants are at higher risk of having medical disabilities in adulthood and are less likely to have higher education, a well-paying job, or a family.

Investigators at the University of Bergen, Haukeland University Hospital, and the Norwegian Institute of Pubic Health, all in Norway, found rates of adult disabilities increased with decreasing gestational age at birth.

The study, with first author Dag Moster, MD, PhD, from the University of Bergen, is published in the July 17 issue of the New England Journal of Medicine.

Using data from the national birth registry, the researchers tracked all infants born in Norway without congenital anomalies between 1967 and 1983. They divided the gestational age into 5 categories:

• 23 weeks to 27 weeks, 6 days.
• 28 weeks to 30 weeks, 6 days.
• 31 weeks to 33 weeks, 6 days.
• 34 weeks to 36 weeks, 6 days.
• 37 weeks or more (reference category).

Precise Linkage

Following these children until 2003, the researchers linked their birth information with information from national registries of medical disabilities, education, income, family status, social security benefits, unemployment compensation, and criminal records. Precise linkage of such records was possible because every resident in Norway has a national identification number that is used by all registries.

Children who died before age 5 years were excluded from the analyses of medical disabilities. They also excluded those who died before age 20 years or who received medical disability benefits from the analyses of education, income, employment, social security benefits, life partner, reproduction, and criminal activity.

For education, investigators included only those whose age made it possible to have attained a particular level. For example, they excluded those who were born after 1980 when assessing completion of a bachelor’s degree.

A total of 903,402 children were born alive between 1967 and 1983 with a gestational age at birth of at least 23 weeks and without congenital anomalies. Of these, 13,582 died before age 20 years and 22,128 were not registered as residents in Norway as adults, leaving 867,692 in the adult cohort.

Five-year survival increased from 20% for children born at 23 to 27 weeks of gestation to 99% for those born at term. The neonatal mortality rates decreased steadily for all gestational ages from 1967 to 1983.

Prevalence of Disabilities

The study found that the prevalence of having cerebral palsy was 0.1% for full-term babies vs 9.1% for those born at 23 to 27 weeks (relative risk for birth at 23 to 27 weeks of gestation, 78.9; 95% CI, 56.5 – 110.0); the prevalence of mental retardation was 0.4% vs 4.4% (relative risk, 10.3; 95% CI, 6.2 – 17.2; and the prevalence of receiving a disability pension was 1.7% vs 10.6% (relative risk, 7.5; 95% CI, 5.5 – 10.0).

The increased prevalence of cerebral palsy coincided with the increase over time of the survival rates of babies with the lowest gestational ages, leaving increased survival as the most likely explanation for the increased prevalence, according to the study authors.

Preterm Disadvantages

Even without medical disabilities, babies born preterm appeared to be at a disadvantage. They were less likely than babies born at term to complete high school (P = 0.003), obtain a bachelor’s degree (P = 0.009) or a postgraduate degree (P=0.006), or have a high income (P < 0.001.These preterm babies were also less likely to find a life partner and to have children, although they were not more likely to be involved in criminal activity.

The authors speculate that the link between premature birth and adverse adult outcomes may represent long-term effects of subtle brain dysfunction caused by the early births.