Spontaneous resolution of fetal nuchal cystic hygroma.

Complete resolution of the hygroma occurred in two fetuses with the mid-trimester ultrasound diagnosis of a nuchal cystic hygroma. Cytogenetic studies showed a normal 46,XX karyotype in one fetus, and a 47,XX, +18 in the other. Complete regression of cystic hygroma has been reported in fetuses with normal chromosomes, as well as in those with trisomy 21, and with Turner's syndrome. The incidence of spontaneous in utero resolution of fetal nuchal cystic hygroma is unknown. The natural history of cystic hygroma in utero cannot be correlated with the chromosome complement. An antenatal karyotype determination should be offered to any patient whose fetus has cystic hygroma, even to those with spontaneous resolution.