What can be hidden behind negative NIPT? Trisomy 18 mosaicism and complex fetal anomalies – case report

Background. First-trimester screening is the most im­por­tant method for detecting major fetal anomalies. Non­in­va­sive pre­na­tal tests (NIPTs) have been used more frequently to evaluate genetic anomalies, but this test must be ac­com­pa­nied by an ultrasound scan of the fetal anatomy. Case re­­port. A 32-year-old woman, thirteen weeks pregnant, with­out risk factors for genetic syndromes, performed as the first screening test, in the first trimester, a NIPT which in­di­ca­ted a reduced probability for the tested genetic ano­ma­lies. She came to our clinic for a screening ultrasound scan that revealed the presence of multiple fetal anomalies: spina bifida with intracranial signs (crash sign, dry brain), in­creased nuchal translucency (3.3 mm), generalized te­gu­men­tary edema, complex cardiac anomaly (common ar­tery trunk, right aortic arch and tricuspid regurgitation), com­plex omphalocele with liver and intestine, unilateral re­nal agenesis, and single umbilical artery. It was decided to terminate the pregnancy. The molecular analysis of the karyo­type resulted in trisomy 18 mosaicism. Conclusions. Non­in­va­sive prenatal testing should not be used as the only screening method for fetal anomalies, even though an ex­ten­ded panel of tests is used. Ultrasound scanning has a pri­mary role in the detection of fetal anomalies.