RESUMEN
OBJECTIVE: To evaluate the thymic-thoracic ratio (TT ratio) on fetal ultrasound and its association with conotruncal heart defects. METHODS: A case control study was carried out to retrospectively assess the TT ratio on fetal echocardiograms performed between 19 and 39 weeks of gestation, showing congenital heart defects, from January to December 2018. The control group was comprised of fetuses with no echocardiogram evidence of congenital cardiac malformations. Cases of multiple pregnancies and patients where the TT ratio could not be established have been excluded. RESULTS: A total of 338 pregnancies have been analysed. Fifty-two pregnancies were diagnosed with fetal heart defects (15%), 17 of which showed conotruncal heart defects (32.7%). The TT ratio in normal fetuses (286 pregnancies) increased with gestational age, and had an average of 0.43 ± 0.06. Compared to the control group (normal fetuses), fetuses with conotruncal heart defects had significantly lower mean TT ratio (0.33 ± 0.07). Those that were diagnosed with nonconotruncal heart defects did not show any statistically significant difference in the TT ratios compared with the control group (0.40 ± 0.09 vs. 0.43 ± 0.06, respectively). CONCLUSION: The TT ratio was significantly lower in fetuses with conotruncal heart defects compared with both the control group (normal fetuses) and the fetuses with nonconotruncal heart defects.