Maxillo-occipital line: a sonographic marker for screening of open spina bifida in the first trimester of pregnancy.

To describe a new first-trimester sonographic landmark the maxillo-occipital line which may be useful for early screening of open spina bifida. Maxillo-occipital line was prospectively evaluated in 100 low-risk pregnancies at the time of first-trimester sonographic screening examination between 11 and 13 + 6 weeks' gestation. All the pregnant women subsequently had a normal second-trimester scan and normal outcomes. Midsagittal brain images of 14 fetuses with known diagnosis of open spina bifida were evaluated retrospectively to review the maxillo-occipital line. None of the 100 fetuses evaluated prospectively with the maxillo-occipital line below the junction of the midbrain and brain stem were affected by open spina bifida. The aqueduct of Silvius to occiput distance measurement was not obtained in five cases. In all, 14 cases with a diagnosis of open spina bifida, the junction between the midbrain and brain stem, were below the maxilla-occipital line. Maxillo-occipital line is an easy addition to the evaluation of first-trimester screening of open spina bifida. Further studies are needed to determine the false-positive and false-negative rates of this technique.