Fifth digit measurement in normal pregnancies: a potential sonographic sign of Down's syndrome.

The objective of the study was to obtain measurements of the fetal fifth finger, as a basis for further studies and for future comparison with fetuses with Down's syndrome. The study group included 173 karyotypically normal fetuses at 15-23 weeks' gestation. Routine biometric measurements were obtained on all, including biparietal diameter (BPD), femoral length (FL) and humeral length (HL), and the length of the fetal fifth finger. Linear growth of the fifth finger was observed across the range of gestational ages (GA), and a linear correlation was shown to exist between the length of the fifth finger and gestational age (y = -7.804 + 0.9079 x GA; r = 0.923; p < 0.0001), biparietal diameter (y = -3.7010 + 0.3043 x BPD; r = 0.913; p < 0.0001), femoral length (y = -0.0983 + 0.3406 x FL; r = 0.926; p < 0.0001), and humeral length (y = -1.3453 + 0.3982 x HL; r = 0.929; p < 0.0001). These results provide normative data of the length of the fetal fifth finger across a range of gestational ages. These data may provide an additional screening parameter for the prenatal detection of Down's syndrome.