In a group of 810 singleton pregnancies without malformations or chromosomal abnormalities blood flow velocity wave forms of the umbilical artery were recorded in the third trimester by means of a pulsed duplex Doppler system. We calculated the pulsatility index (PI). 133 newborn with a birthweight below the 10th centile were classified as small-for-gestational-age (SGA) (prevalence: 16%). The sensitivity of the test (elevated PI) for these neonates is 52% and the specificity 97%, the positive predictive value is 78% and the negative predictive value 91%. Therefore, Doppler Sonography of the umbilical artery is not an appropriate screening test to identify SGA babies prenatally. The results for jeopardized SGA babies (caesarean section because of pathological CTG traces, transfer to the neonatal intensive care unit) are much better. 31 out of 133 belonged to that group. For these foetuses, the sensitivity of the test is 94% and the negative predictive value 97%. Hence, Doppler Sonography of the umbilical artery allows very well to identify the endangered SGA foetuses on the one hand and to exclude foetal jeopardy with a normal PI on the other.