Increased Umbilical Artery Pulsatility Index in Third-Trimester Fetuses with Trisomy 21

To examine the umbilical arterial Doppler flow patterns in late third-trimester fetuses with trisomy 21.

This is a retrospective study on fetuses with trisomy 21 that were evaluated after 33 weeks' gestation at the Department of Obstetrics and Gynaecology of the University of Tuebingen, Germany. The umbilical and the middle cerebral artery (UA and ACM) pulsatility index (PI) measurements and the abdominal circumference were transformed into z-values.

Forty-two fetuses met the study criteria. The mean gestational age at the time of the first and the second visit was 35.0 and 36.6 weeks, respectively. The mean UA PI was 1.31 and 1.38, which corresponds to z-values of 2.20 and 2.70. In 24 (57.1%) cases, both PI measurements were above the 95th centile. A linear regression analysis demonstrated that the mean of both UA PI was not dependent on the abdominal circumference or on any other examined maternal and pregnancy characteristics. The mean ACM PI at the first and the second visit was 1.62 and 1.48, respectively, corresponding to mean z-values of -0.59 and -0.75, and in none of the cases was it below the 5th centile.

In half of the third-trimester fetuses with trisomy 21, the resistance in the UA is increased - even in the absence of placental insufficiency.