THE SIGNIFICANCE OF UMBILICAL VEIN DOPPLER CHANGES DURING FETAL HICCUPS

Objective: The physiology of hiccups is a sharp inspiratory gasp again st a closed glottis, causing a sudden sharp fall in intrathoracic pres sure. This would be expected to cause an increase in venous return to the chest; however, we noticed that umbilical venous Doppler waveforms indicated a cessation of flow during hiccups. We observed other hiccu ping fetuses to ascertain the range of response of the fetal umbilical vein Doppler waveforms and derive an explanation for them. Methods: F etuses who were hiccuping at the time of their antepartum testing had observations of umbilical vein flow made, and representative recording s of the trace were obtained. Results: Ten Doppler traces were obtaine d from fetuses during hiccuping. Tn every case there was a brief fall of the umbilical vein Doppler waveform to base line, indicating an arr est of flow. Conclusions: Fetal hiccups are associated with arrest of flow in the umbilical vein as demonstrated by Doppler waveforms. This is contrary to predictions based on previously demonstrated fetal phys iology of hiccups. We speculate that the findings result from obstruct ion of the venous return by a combination of the contracting diaphragm at the level of the inferior vena cava as it passes through the diaph ragm, by raised intra-abdominal pressure from the descending diaphragm , and possibly from kinking of the umbilical vein at the umbilical rin g.