P01.05: Relationship between fetal thymus size and cervical length in the second trimester of pregnancy and the risk of preterm birth

Abstract

The purpose of this study was to investigate if there is a relationship between cervical length in the second trimester of pregnancy and fetal thymus size as a potential marker for preterm birth. 79 pregnant women were invited to participate in this study. The inclusion criteria were singleton pregnancy, gestational age between 19+0 and 24+6 weeks, absence of signs of premature rupture of membranes and absence of fetal malformations and congenital infections. These patients were evaluated by transvaginal ultrasound to the measurement of cervical length. It was considered short cervix if less than 25 mm. Fetal thymus size was analysed in the three-vessel view of thorax and its transverse diameter was measured by only one observer. Three measurements were obtained and the median calculated was then transformed into Z-score (SD values from the mean). The pregnant women were divided in two groups: Short Cervix (SC – 22 pregnant women) and Normal Cervix (NC – 57 pregnant women). Both groups had similar characteristics and the mean gestational age of evaluation was 22 weeks. Analysing Z-score values, the fetal thymus transverse diameter was increased in the Short Cervix group (2,708 SC vs -0,043 NC, p=0,003). Despite of the previous studies showed fetal thymus involution as a marker of the fetal inflammatory response syndrome in cases of PROM and a predictor of chorioamnionitis in the third trimester. However, we found that patients in the second trimester, the fetal thymus was increased in cases of short cervix. The hypothesis is this finding is related to initial inflammatory response of thymus due to a chronic and subclinical infection or inflammation.