Presence of the 'lemon' sign in fetuses with spina bifida at the 10-14-week scan.

In three cases of lumbosacral spina bifida diagnosed at 12, 13 and 14 weeks of gestation there was an associated lemon sign, or scalloping of the frontal bones, and in one case the fetal nuchal translucency was increased. In a multicenter ultrasound screening study at 10-14 weeks there were 61,972 singleton pregnancies including 29 cases of spina bifida, none of which was diagnosed at the routine first-trimester scan, but 28 of the 29 cases were detected by ultrasonography at 16-22 weeks; in one case the diagnosis was missed at the 20-week scan and the defect was identified at 32 weeks during a scan for localization of the placenta. The fetal nuchal translucency was above the 95th centile in only one of the cases (3.4%). It is possible that the majority of fetuses with spina bifida have a lemon sign in the first trimester, but the sensitivity of the 10-14-week scan in the diagnosis of spina bifida and the prevalence of the lemon sign at this gestation will only be established by further studies incorporating early systematic examination of the head and spine.