P09.11: Maxillo-occipital line: a sonographic marker for the screening of open spina bifida in the first trimester

To describe a new first-trimester sonographic landmark, the maxillo-occipital line, which may be useful in the early screening of open spina bifida. The Maxillo-occipital line is a straight line drawn along the superior border of the maxilla until it reaches the inner border of the occiput in the mid sagittal plane of the fetal face. In normal fetuses at 12–13 weeks the junction between the midbrain and brain stem is above this line. In case of open spina bifida, the line is below the junction of the midbrain and thalamus. The maxillo-occipital line was prospectively evaluated in 100 low risk pregnancies at the time of routine first trimester sonographic screening at 11+ 0 to 13 + 6 weeks' gestation. All these women subsequently had a normal 20 week morphology scan and normal outcome. Mid sagittal brain images of 14 fetuses with a known diagnosis of open spina bifida were evaluated retrospectively to review the maxillo-occipital line in the mid sagittal plane, taken to measure the nuchal translucency. In all the cases with a diagnosis of open spina bifida, the junction between the midbrain and brain stem was below 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 maxillo-occipital line is an easy addition to the evaluation of the first trimester assessment of the Nuchal translucency and fetal brain. The contribution of this sign in the early detection of spina bifida remains to be determined in larger studies. Further studies are needed to determine the false-positive and false-negative rates of this technique.