The fetal profile line: a proposal for a sonographic reference line to classify forehead and mandible anomalies in the second and third trimester.

Objectives: To test the fetal profile (FP) line, defined as the line that passes through the anterior border of the mandible and the nasion, as a reference line for forehead and mandible anomalies.

Methods: Volumes of 248 normal and 24 pathological fetuses (16-36 and 19-37 weeks' gestation, respectively) were analysed retrospectively. When the FP line passes anteriorly, across or posteriorly to the frontal bone, this was defined as 'negative', 'zero' or 'positive', respectively. When the FP line was positive the distance (F distance) between the FP line and the frontal bone was measured.

Results: No cases with a negative FP line were found in the normal fetuses. Before 27 weeks' gestation the FP line was always 'zero' except in one case. After 27 weeks' gestation the FP line was 'positive' in up to 25% (F distance (mean, range): 2.8, 2.1-3.6 mm). The FP line correctly identified 13 cases with retrognathia, 5 cases with frontal bossing and 3 cases with a sloping forehead.

Conclusion: Although large prospective studies are needed, the FP line may be a useful tool to detect second trimester profile anomalies such as retrognathia, sloping forehead and frontal bossing with the possibility of quantifying the latter.