Cystic hygroma: comparison between prenatal and postnatal diagnosis.

Antenatal diagnosis of congenital malformation often leads to opportunities for intervention in the pregnancy that may have a profound effect on the outcome of the fetus. The accuracy of the diagnostic technique is a critical factor in judging the appropriateness of such interventions. This article reports the current accuracy of prenatal ultrasound diagnosis of cystic hygroma (CH) in a region with a population of 3.5 million and an annual birth rate of 52,000. During a 32-month period (to December 1994), 113 diagnoses of CH were reported to the South East Thames Regional Congenital Malformation Registry. Eighty-nine diagnoses were made prenatally and 24 were made postnatally (at delivery or postmortem). The number of confirmed cases of CH was 52 (46% total diagnoses). The prenatal diagnoses were established at a mean gestational age of 19 weeks. Fifty-six (63%) pregnancies with a prenatal diagnosis of fetal CH were terminated; in only 25% of these was the presence of CH confirmed after termination. Overall, of the 89 prenatal diagnoses, 28 (32%) were confirmed, 45 (50%) were incorrect, and 16 (18%) could not be confirmed or refuted. Only 24% of fetuses with a prenatal diagnosis of CH were live born. The survival rate at 1 year for the live-born infants with CH in this series was 88%. The diagnosis of fetal CH has a recognised association with chromosomal abnormalities, and consequently may lead to termination of the pregnancy. A potential error rate of almost 70% in the prenatal ultrasound diagnosis of this condition requires clinicians to adopt a more cautious approach to the management of the fetus with "cystic hygroma."