The diagnosis of fetal microcephaly.

Of 16 fetuses in whom microcephaly was suspected, nine (56.2%) were affected with microcephaly, and seven (43.8%) were unaffected. Subsequently, nomograms with mean and SDs for biparietal diameter, occipitofrontal diameter, head perimeter: bdominal perimeter, biparietal diameter:femur length, and femur length:head perimeter we derived. With the use of the data from 27 sonograms of the 16 fetuses, different thresholds of abnormality were tested. Three standard deviations from the mean for biparietal diameter, occipitofrontal diameter, head perimeter, and femur length:head perimeter were sensitive thresholds for the diagnosis of fetal microcephaly with no false negative diagnoses. Four standard deviations from the mean for occipitofrontal diameter, head perimeter:abdominal perimeter, and femur length:head perimeter were specific tests with no false positive diagnoses. The use of multiple diagnostic tests was necessary to improve accuracy in the diagnosis of fetal microcephaly. Further clinical studies are needed to delineate more clearly optimal tests and thresholds of abnormality.