title: Second-Trimester Sonographic Thymus Measurements Are Not Associated With Preterm Birth and Other Adverse Obstetric Outcomes.
abstract: OBJECTIVE
  Previous studies have demonstrated an association between adverse obstetric outcomes, such as preterm birth, and in utero inflammation. The fetal thymus, which can be visualized in the anterior mediastinum on obstetric sonography, may involute in response to such inflammation and thus may identify pregnancies at increased risk for these outcomes. We therefore sought to determine whether second-trimester fetal thymus measurements are associated with preterm birth.
  
  
  METHODS
  Transabdominal fetal thymus measurements were prospectively obtained in singleton pregnancies at gestational ages of 18 weeks to 23 weeks 6 days during a 5-month period. The transverse and anterorposterior thymus diameters and the thymic-thoracic ratio were measured. Delivery outcomes were collected from our clinical database. The primary outcome was preterm birth, which we defined as delivery between 24 weeks and 36 weeks 6 days. Small for gestational age (SGA) and pregnancy-related hypertension, which are adverse obstetric outcomes that may also be associated with in utero inflammation, were included as secondary outcomes.
  
  
  RESULTS
  We included 520 patients with thymus measurements and obstetric outcome data. The prevalence of preterm birth was 12.3% (n = 64). None of the thymus measurements were associated with preterm birth. Similarly, there was no association between thymus measurements and SGA or pregnancy-related hypertension.
  
  
  CONCLUSIONS
  Sonographic assessment of the second-trimester fetal thymus did not identify patients at increased risk for preterm birth, SGA, and pregnancy-related hypertension. Routine thymus measurements during the second-trimester anatomic scan are not clinically useful for prediction of preterm birth and other adverse outcomes.
authors.affiliation: Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania USA. jbrandt@hackensackumc.org.
authors.forename: Justin S
authors.initials: JS
authors.lastname: Brandt
authors.affiliation: Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania USA.
authors.forename: Jamie A
authors.initials: JA
authors.lastname: Bastek
authors.affiliation: Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania USA.
authors.forename: Eileen
authors.initials: E
authors.lastname: Wang
authors.affiliation: Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Purisch
authors.affiliation: Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania USA.
authors.forename: Nadav
authors.initials: N
authors.lastname: Schwartz
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000000981:diagnostic imaging*; D007236:Infant, Small for Gestational Age; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D047928:Premature Birth / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D013950:Thymus Gland / Q000000981:diagnostic imaging* / Q000196:embryology*; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: fetal growth restriction; fetal thymus; obstetric ultrasound; preeclampsia; preterm birth; screening; second trimester