title: Assessment of first-trimester thymus size and correlation with maternal diseases and fetal outcome.
abstract: BACKGROUND
  We investigated the reliability of fetal thymus measurement during first-trimester screening, and associated fetal thymus size with crown-rump length, maternal diseases and fetal outcome.
  
  
  METHODS
  In a retrospective cohort of 971 normal singleton first-trimester fetuses, we measured the anterior-posterior diameter of the thymus in a midsagittal plane in 767 fetuses. The intra-observer and inter-observer reliabilities were tested by intra-class correlation coefficient. We correlated thymus size with fetal crown-rump length, and investigated its association with maternal diseases (diabetes mellitus, rheumatic disorders, hypertension and coagulation disorders) and fetal outcome (small for gestational age, preterm birth and umbilical artery pH) using regression analyses.
  
  
  RESULTS
  The intra-observer and inter-observer reliabilities of fetal thymus measurement were excellent (intra-class correlation coefficient 0.926, 95% CI 0.745-0.981 and 0.945, 95% CI 0.886-0.993, respectively). A linear relationship was found between crown-rump length and thymus size (β = 0.023, p = 0.001). Pregnancies affected by maternal diabetes had a decreased fetal thymus size (β = -0.209, p = 0.001), whereas in pregnancies affected by maternal rheumatic disease the thymus size was increased (β = 0.285, p < 0.001). Fetal thymus size was not associated with maternal hypertension or maternal coagulation disorders. There was a positive association between preterm birth and fetal thymus size (p < 0.001).
  
  
  CONCLUSIONS
  Measurement of first-trimester thymus size is reliable. Fetal thymus size has a linear correlation with crown-rump length. Maternal diabetes, rheumatic disease and preterm birth appear to have an association with fetal thymus size.
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.
authors.forename: Judith M A
authors.identifier: http://orcid.org/0000-0002-2174-6368
authors.initials: JM
authors.lastname: Borgelt
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.
authors.forename: Mareike
authors.identifier: http://orcid.org/0000-0003-2331-2317
authors.initials: M
authors.lastname: Möllers
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.
authors.forename: Maria K
authors.identifier: http://orcid.org/0000-0002-0160-686X
authors.initials: MK
authors.lastname: Falkenberg
authors.affiliation: Institute of Biostatistics and Clinical Research, University of Münster, Münster, Germany.
authors.forename: Susanne
authors.identifier: http://orcid.org/0000-0001-6903-2906
authors.initials: S
authors.lastname: Amler
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.
authors.forename: Walter
authors.identifier: http://orcid.org/0000-0002-9943-1235
authors.initials: W
authors.lastname: Klockenbusch
authors.affiliation: Department of Gynecology and Obstetrics, University Hospital Münster, Münster, Germany.
authors.forename: Ralf
authors.identifier: http://orcid.org/0000-0002-5353-5135
authors.initials: R
authors.lastname: Schmitz
mesh_terms: D018568:Crown-Rump Length; D016640:Diabetes, Gestational; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D009929:Organ Size; D011247:Pregnancy; D011248:Pregnancy Complications; D011261:Pregnancy Trimester, First; D047928:Premature Birth; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012216:Rheumatic Diseases; D012307:Risk Factors; D013950:Thymus Gland / Q000000981:diagnostic imaging* / Q000196:embryology*; D016216:Ultrasonography, Prenatal; D014469:Umbilical Arteries
keywords: Pregnancy; diabetes in pregnancy; fetal development; first trimester; prenatal ultrasonography; preterm birth; thymus gland