[Single umbilical artery. Effect on fetal growth and doppler flow velocity wave form]

Fetuses with single umbilical arteries (SUA) are often small for gestational age (SGA). We tried to clarify the following questions: 1. In which range of the normal reference chart for 2 umbilical arteries are the S/D-ratios of SUA located? 2. Is it possible to correctly predict the fetuses at risk for asphyxia or fetal death using these reference charts in SNA fetuses? 3. How do placental weight and histological findings in the fetoplacental vessel influence flow patterns in SUAs? 4. How does the vessel diameter of SUAs influence fetal growth?

25 fetuses with SUA were examined by means of ultrasound and Doppler ultrasound 1 to 9 times with measurements of arterial diameter and S/D-ratio. These data were compared with results of normal umbilical cords (data from the literature) and correlated with fetal outcome and histological placental findings.

Out of 94 individual measurements the S/D-ratio was found to be below the 10th percentile in 28 cases (30%), between the 10th and 50th percentile in 31 cases (33%), between 50 and 90th 20 cases (21%), and above the 90th percentile of the reference chart in 15 cases (16%). 14 fetuses were SGA, 2 presented an intrauterine death, 2 were born with chromosomal aberrations and 3 with malformations. 5/6 fetuses with caesarean section for asphyxia or fetal demise were correctly detected to show an elevated S/D-ratio, 1 case of intrauterine death was not. 16/19 placentas were found to be of low weight, in 14 we found villous malmaturation. 18/22 examined SNAs had an elevated diameter above the +2s range of the reference chart for normal arteries. The ratio of the diameters of the umbilical vein and artery was above 2 in 12/14 SGA fetuses, indicating that the SNA's diameter was less than 50% of that of the veins in these cases.

Widening of the SNA lumen leads to a reduction of the S/D-ratio. An SNA diameter of less than 50% of that of the vein results in intrauterine growth retardation. Elevated S/D-ratio correctly identifies SNA-fetuses at risk.