title: The development of the fetal thymus: an in utero sonographic evaluation.
abstract: OBJECTIVE
  To establish a nomogram for fetal thymus size during gestation.
  
  
  METHODS
  The study is a prospective, cross sectional evaluation of 403 male and female fetuses between 14 and 38 weeks of normal singleton pregnancies. Measurements of fetal thymus size were performed by high resolution transvaginal ultrasonography between 14 and 17 weeks' gestation, and by transabdominal ultrasonography after 18 weeks' gestation.
  
  
  RESULTS
  Adequate thymus size measurements were obtained in all 403 fetuses. Thymus size as a function of gestational age was expressed by the regression equation: (square root) thymus size (mm)= -39.39+4.41 x gestational age (weeks). The correlation coefficient, r=0.965, was found to be highly statistically significant (p<0.0001). The normal mean and the 90% prediction limits were defined.
  
  
  CONCLUSIONS
  The present data offer the normal range of fetal thymus size from early stages of gestation that may allow intrauterine assessment of its development. It may be helpful in the prenatal diagnosis of thymic pathologies.
authors.affiliation: Department of Obstetrics and Gynecology, The Chaim Sheba Medical Center, Tel-Hashomer, Ramat Gan, Israel. zalel_y@netvision.net.il
authors.forename: Yaron
authors.initials: Y
authors.lastname: Zalel
authors.forename: Ronni
authors.initials: R
authors.lastname: Gamzu
authors.forename: Shlomo
authors.initials: S
authors.lastname: Mashiach
authors.forename: Reuven
authors.initials: R
authors.lastname: Achiron
mesh_terms: D005260:Female; D005865:Gestational Age; D006801:Humans; D008297:Male; D011247:Pregnancy; D012016:Reference Values; D012044:Regression Analysis; D013950:Thymus Gland / Q000000981:diagnostic imaging* / Q000196:embryology*; D016216:Ultrasonography, Prenatal