The early and accurate detection of intrauterine infection is an important challenge in clinical obstetrics. Currently there are no reliable clinical markers to adequately indicate subclinical intrauterine infection. The thymus gland perimeter and transverse diameter were evaluated sonographically concluding that there was a progressive increase in thymus gland size with progressing gestational age. Recent studies have shown a strong correlation between fetal thymus involution and the presence of chorioamnionitis and funisitis in preterm labor.