[Cephalic index: a neglected parameter of standard fetal biometry]

From 1.1.1990 to 15.3.1991, in 1074 women between the 13th and 40th weeks of pregnancy, the biparietal diameter (BIP), fronto-occipital diameter (FOD) and kephalic index (KI = BIP/FOD) were measured. The median of the kephalic index varied between 0.81 and 0.84 during different pregnancy weeks, with a range between 0.67 and 1.00. Correction to normokephaly (KI = 0.84) produced differences of up to 10 mm to measured values of BIP. We believe it necessary to determine the kephalic index in each kephalometry and to correct the measured value of BIP at least in those cases where the measured kephalic index differs significantly from normokephaly (KI = 0.84).