The relationship between sonographic fetal thymus size and the components of the systemic fetal inflammatory response syndrome in women with preterm prelabour rupture of membranes.

OBJECTIVE: To assess the relation between sonographic fetal thymus size and the components of fetal inflammatory response syndrome (FIRS) in women with preterm prelabour rupture of membranes (PPROM).

DESIGN: Prospective cohort study.

SETTING: University hospital from January through October 2006.

POPULATION: Fifty-six women with PPROM.

METHODS: In these women, fetal thymus perimeter was measured sonographically. At birth, cord venous plasma interleukin-6 (IL-6) level estimation and histopathological examination of the placentas and umbilical cords were performed.

MAIN OUTCOME MEASURES: Small thymus size (< 5th percentile for gestational age) and its association with FIRS.

RESULTS: From the 56 women with PPROM, 54% had chorioamnionitis (CA), 23% had funisitis. IL-6 level was > 11 pg/ml in 52% of women and > 18 pg/ml in 41%. A small thymus was more associated with male fetuses, shorter preterm prelabour rupture of membranes delivery interval, higher IL-6 level, higher frequency of funisitis and CA. When data were regressed for confounding, only IL-6 level and funisitis remained significant independent factors that influence the thymus size. In the subset of women (n = 19) who delivered within 1 week of first measurements, a small thymus had sensitivity and positive predictive value of 93%, specificity and negative predictive value of 75% and accuracy of 89% in the identification of FIRS (IL-6 >18 pg/ml and/or funisitis).

CONCLUSIONS: An association exists between fetal thymic involution and components of FIRS in women with PPROM. Small fetal thymus size may be considered a reliable sonographic marker of fetal involvement in the inflammatory response.