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351: Prenatal assement of the fetal thymus: utility of 2D and 3D ultrasound in healthy fetuses

      Objective

      To present the normative data of the volume of the developing fetal thymus and compare fetal thymus volume by 3D ultrasound (3D-US) with 2D ultrasound (2D-US) measurements.

      Study Design

      We studied 135 consecutive normal singletons between 18 and 38 weeks gestation, measuring thymic maximum transverse diameter (MTD) anterior-posterior diameter (APD), superior-inferior diameter (SID), maximum transverse area (MTA) based on previously described methods. Thymus volume (TV) was obtained by 3D-US using VOCAL. Linear regression was used to assess the correlation between individual measurements corrected for estimated fetal weight and the gestational age (GA). A p<0.05 was considered statistically significant. Institutional review board approval obtained prior to the study.

      Results

      Ultrasound assessment of the fetal thymus was possible in 90.4% of the cases. Both 3D-US and 2D-US measurements were significantly correlated with GA (TV r = 0.97, P < 0.001; MTA r= 0.79; MTD r=0.49; APD r= 0.57; SID r= 0.45; all p < 0.01).

      Conclusion

      We present the first normative data of the volume of the developing fetal thymus. 3D-US fetal thymus volume can be obtained in a majority of cases and is more significantly correlated to GA than the MTD, APD, AID and MTA. Assessment of the fetal thymus may be indicated where conditions that could affect the thymic size are suspected (e.g. fetal infections, diGeorge syndrome).
      Tabled 13D Fetal Thymus Volume (mL) During Pregnancy
      GAPercentile
      5th50th95th
      18-200.931.522.03
      20-221.762.032.45
      22-242.132.393.37
      24-263.704.354.53
      26-284.275.405.60
      28-386.277.279.47