INTRODUCTIONTrisomy 9 is a rare genetic alteration that represents 2.7% of all trisomies. (1,2,7) It was reported for the first time in 1973 by Feingold and Atkins, through the study of lymphocytes in the blood of a male newborn, with multiple congenital anomalies (4,5). Complete gain of chromosome 9 has a fatal prognosis and usually results in first trimester miscarriage. (2) However, in exceptional cases, pregnancies that reach term die in the early neonatal period (4).From the cytogenetic point of view, cases of trisomy 9 present completely, which is not mosaicism, or in a state of mosaicism. The spectrum of this syndrome, in addition to trisomy 9, includes partial trisomies of the short arm 9p, of the long arm 9q, mosaicisms, mosaicisms confined to the placenta and pseudo mosaicisms. (4,5). In the case of trisomy 9, most correspond to de novo mutations. Mosaicisms are related to balanced rearrangement mutations (5). However, phenotypic heterogeneity, as well as the incidence and severity of associated malformations, are directly related to the variable size of the duplicated segment and the frequent concomitant monosomy (2,3,4,6).Most of the cases of trisomy 9 reported in the literature occurred in women under 35 years of age, which makes evident the usefulness of screening for congenital anomalies, even in low-risk populations (1,2). Fetal screening in the first and second trimesters allows early detection of fetal structural abnormalities associated with genetic alterations. In this way, it offers the opportunity to advise the patient, with the aim of carrying out early interventions regarding the prenatal prognosis and postnatal management, even if it is available and for this specific case, the interruption of the pregnancy. (1)(6).This chromosomal abnormality is characterized by a constellation of multiple phenotypic abnormalities that mainly involve craniofacial, central nervous system, cardiovascular, musculoskeletal, and genitourinary abnormalities (1,4,5,7). The main structural anatomical alterations include, for ultrasound screening at 11-13.6 weeks, an increase in the thickness of nuchal translucency (1), then microcephaly and brachycephaly become evident, fontanelles and wide cranial sutures, bulbous nose, lip and cleft palate, short nasolabial fold , hypertelorism, micro-retrognathia, short and wide neck and low implantation of the ears. In the central nervous system, it is common to find associated Dandy Walker Malformation characterized by hydrocephalus, alterations in the development of the cerebellar vermis and ventriculomegaly (4,2). At the cardiovascular level, it is common to find ventricular septal defects, cardiomegaly, valvular dysplasia or even the right aortic arch. Regarding the musculoskeletal system, camptodactyly, clubfoot , hypoplasia or agenesis of the fingers and nails of the hands and feet (4), and dislocation of the hip or knees can be found. In genitourinary organs, horseshoe kidney, renal hypoplasia or dysplasia as well as renal cysts, short penis or bicornuate uterus become evident . Other case reports include abnormal lung lobulation, malrotation, hypoplasia or agenesis of the gallbladder and biliary tract, and hypoplasia of the adrenal gland. In addition, this pathology incorporates within its recognition pattern growth restriction, low birth weight and delayed neurological development. (2,7) Other authors mention that, when faced with elevated serum levels of alpha-fetoprotein in the context of trisomy 9, the finding of spina bifida should be ruled out (1). Serum markers such as the free fraction of BhCG and PAPP-A are found to be decreased in concentration in trisomies 9 and 18. In addition, different abnormal phenotypic findings overlap in both chromosomopathies; however, the genetic study can discern the final diagnosis (1,4).