Perinatal outcome in fetuses with extremely large nuchal translucency measurement

Background: Studies have suggested that an entirely normal outcome is likely when the nuchal translucency (NT) measurement is very large and the karyotype, morphology and echocardiography scans are normal. Recently this has been questioned as it is based on very small numbers.
Aim: Assess the outcome of pregnancies with an NT measurement of 6.5 mm or greater.
Methods: Audit of a large first trimester screening program.
Results: Over the ten years to 2006, 76 813 patients underwent first trimester screening, with 120 having an extremely large NT. Thirty-one cases had normal karyotypes, of which there were four sets of twins that demised. Six cases miscarried and ten were terminated, some with morphological abnormalities. Eight cases were still alive for the morphology scan, with the only abnormality being mild pyelectasis in one case. At birth, three cases were normal and another three cases had a good outcome. Two cases had coarctation of the aorta and a good outcome. One case had Noonan's syndrome, another had cerebral palsy and the case with pyelectasis had hydronephrosis, dilated ureters and some contractures.
Conclusions: When the karyotype and morphology scan are normal, the outcome is often good in spite of an extremely large NT. However, even a subtle ultrasound anomaly can indicate a genetic syndrome and echocardiography cannot exclude mild cardiac abnormalities.