First-trimester simple hygroma: Cause and outcome

Objective: First-trimester fetuses with simple nuchal hygromas represent a population that is different from midgestation nuchal cystic hygroma in terms of karyotype abnormalities and long-term prognosis. Study Design: Sixty-eight consecutive fetuses diagnosed with simple nuchal hygromas between 10 and 14 weeks' gestation were evaluated ultrasonographically and karyotyped. Those with normal chromosome complements were ultrasonographically monitored throughout the remainder of the pregnancy for resolution of their hygromas. Results: Twenty-three of 27 fetuses with normal karyotypes resolved their hygromas within 4 weeks of diagnosis and were phenotypically normal at birth. Forty-one fetuses were karyotypically abnormal, with trisomy 21 being the most common abnormality. Conclusions: Fetuses with first-trimester simple nuchal hygromas are at high risk for aneuploidy and should be offered prenatal testing. Such fetuses with normal karyotypes will likely resolve their hygromas by 18 weeks' gestation, and most will be phenotypically normal at birth.