Low thymic size in preterm infants in the neonatal intensive care unit, a possible marker of infection? A prospective study from birth to 1 year of age.

AIM

To study the growth of the thymus in preterm infants.

METHODS

Ultrasonographic thymic size (Ti) was studied in 80 preterm infants (gestational age 24-36 weeks) from birth to discharge from the neonatal intensive care unit (NICU). Thirty-three of these infants were followed to 1 year of age.

RESULTS

At birth, the median Ti was 5.2 compared with 11.8 in term infants. At discharge, the median Ti was 10.0 and not significantly different from Ti in term infants at birth (p = 0.22). The size of the thymus was significantly associated with postmenstrual age and weight (both p < 0.01). Infections during admission were negatively associated with the size of the thymus (p < 0.01). During the first 3 months after discharge, preterm infants had a significantly higher frequency of infections than did term infants (p = 0.002); hereafter, the preterm infants had significantly fewer infections than term infants (p = 0.002). The median Ti in preterm infants and term infants at 1 year of age was 21.1 and 17.3, respectively. This difference was not statistically significant (p = 0.41).

CONCLUSIONS

Growth of thymus was not compromised by preterm birth. Ti is negatively associated with the frequency of infections in preterm neonates submitted to NICU.