ST waveform changes during repeated umbilical cord occlusions in near-term fetal sheep

Am J Obstet Gynecol. 2001 Mar;184(4):743-51. doi: 10.1067/mob.2001.111932.


Objective: This study was undertaken to determine whether changes in the fetal ST waveform during repeated umbilical occlusion reflect the development of hypotension and acidosis.

Study design: Chronically instrumented, near-term fetal sheep received 1-minute total umbilical cord occlusion either every 5 minutes for 4 hours (1:5 group, n = 8), or every 2.5 minutes until blood pressure fell <20 mm Hg on 2 successive occlusions (1:2.5 group, n = 8).

Results: Umbilical cord occlusion caused variable decelerations, with sustained hypertension in the 1:5 group and little change in acid-base status (pH = 7.34 +/- 0.07 after 4 hours). In contrast, the 1:2.5 group showed progressive hypotension and metabolic acidemia (pH 6.92 +/- 0.1 after the final occlusion). There was a marked increase in ST waveform height during occlusions; this increase was greater in the 1:2.5 group (P <.001), but there was overlap between the groups. ST waveform height between occlusions was significantly higher in the 1:2.5 group (P <.001) until negative and biphasic ST waveforms developed in these fetuses between occlusions in the final 30 minutes.

Conclusion: ST waveform elevation occurs during umbilical cord occlusions but only crudely reflects the severity of hypoxia. Interocclusion waveform height may be a better reflection of the severity of hypoxia. The appearance of biphasic and negative waveforms between occlusions may be a useful marker for severe decompensation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acidosis / etiology
  • Acidosis / physiopathology
  • Animals
  • Blood Pressure
  • Constriction
  • Electrocardiography*
  • Female
  • Fetal Hypoxia / complications
  • Fetal Hypoxia / etiology
  • Fetal Hypoxia / physiopathology*
  • Fetus / blood supply
  • Gestational Age*
  • Heart Rate, Fetal*
  • Hydrogen-Ion Concentration
  • Hypotension / etiology
  • Hypotension / physiopathology
  • Pregnancy
  • Sheep
  • Umbilical Cord*