Near-Term Infants at Risk for Poor Health in Childhood

Ricki Lewis, PhD

March 05, 2012

March 5, 2012 — Moderate and late preterm (32 - 36 weeks' gestation) and early-term (37 - 38 weeks' gestation) infants are at higher risk for certain adverse health outcomes during early childhood, indicating that risk follows a continuum, rather than a dichotomy of preterm and term, according to a study published online March 1 in the British Medical Journal.

Elaine M. Boyle, MD, from the University of Leicester, United Kingdom, and colleagues analyzed longitudinal data on 18,818 infants born in the United Kingdom between September 2000 and August 2001 who were enrolled in the Millennium Cohort Study. The current analysis assesses the association of gestational age with various health measures for 14,273 infants at 3 years and 14,056 infants at 5 years.

Outcome measures were growth (height, weight, and body mass index), illness or disability lasting more than 3 months, wheezing and asthma, prescription drug use, hospital admissions unrelated to accidents, and how parents rated their children's health. Children were assessed at home at 9 months, 3 years, and 5 years of age. Parents provided the information on gestational age at birth, hospitalizations, long-term illness, wheezing and asthma, prescription drug use, and evaluation of overall health, thereby introducing possible recall bias.

Infants born between 32 and 36 weeks fall into a gray area between preterm and term infants and are less well studied. However, a previous investigation that found continuing elevated risk at 37 to 38 weeks' gestation inspired the current study.

Dr. Boyle and colleagues discovered "a gradient of worsening health outcomes with decreasing gestation at birth" that "extended across the whole range of gestational age groups, from very preterm to full term, suggesting a 'dose-response' effect of prematurity," they write. However, the late-preterm group had the highest proportion of obesity at 3 and 5 years. The most common indications for hospitalization were gastrointestinal or respiratory problems.

The elevated health risks of late preterm and early-term infants may affect public health to a greater extent than do the medical problems of early-preterm infants because the number of older-gestation babies is so much greater. For example, population attributable fractions for 3 or more hospitalizations from 9 months to 5 years were 5.7% (95% confidence interval [CI], 2.0% - 10.0%) for birth at 32 to 36 weeks and 7.2% (95% CI, 1.4% - 13.6%) for birth at 37 to 38 weeks compared with 3.8% (95% CI, 1.3% - 6.5%) for children born very preterm (<32 weeks).

"Our results challenge widely held views that long term health outcomes for moderate and late preterm babies are similar to those for babies born at full term," the authors write. Even babies born early term are at higher risk, they add.

One reason that the more mature preterm babies (32 - 36 weeks) may have increased risks for poorer health outcomes is that the group includes infants with induction or cesarean delivery resulting from obstetric complications, perhaps implicating an intrauterine problem rather than prematurity.

The researchers suggest that gestation-related risks be considered along a continuum, rather than along a dichotomous distinction of preterm vs term births.

The Bupa Foundation supported this study. The authors have disclosed no relevant financial relationships.

BMJ. Published online March 1, 2012. Full text

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