Introduction:

the interest in sonographic visualization of the fetal thymus is related to its important immunological function, the diagnostic possibilities offered by high-resolution ultrasound scanners, and the increased reporting of possible conditions during the gestation process.

Objective:

to determine the frequency of fetal thymic hypoplasia in pregnant women with genetic risks and to relate it to the presence of fetal defects, previous risk factors and the appearance of adverse obstetric effects.

Methods:

we conducted a prospective descriptive study consisting of the ultrasound evaluation of the fetal thymus by means of the thymic-thoracic ratio in 221 pregnant women who come to referral services of the Provincial Center of Medical Genetics, because they presented increased genetic risk for heart disease.

Results:

sixteen fetuses were found with a thymic-thoracic ratio less than or equal to 0.30, which was used as the criterion for thymic hypoplasia in this study: four with heart diseases, four with chromosomal diseases, one with isolated structural malformation, two with preeclampsia, one with delayed intrauterine growth, one preterm and one fetal death. The reference reasons with the highest proportion of positivity were: increased nuchal translucency and image of suspected congenital cardiopathy in screening ultrasound.

Conclusions:

determination of the thymic-thoracic ratio allowed us the diagnosis of thymic hypoplasia, both in the second and third trimester of pregnancy. This type of research is relevant because it helps to identify: congenital defects, risk factors and adverse obstetric effects.