[Influence of circadian rhythm on fetal and maternal Doppler parameters--is a diurnal variation detectable?]

Doppler sonography is an established method in fetal medicine. Up to now a possible circadian rhythm of fetal and maternal Doppler parameters has only been insufficiently characterized and documented. This survey aimed at evaluating the significance of Doppler parameters with regard to diurnal variations. We have analyzed whether or not a circadian rhythm of fetal and maternal Doppler parameters is detectable.

A non-selected collective of 100 patients with a singleton pregnancy between the 20th and 39th week of gestation was examined with Doppler sonography at the Medical School of Hannover. Besides the Doppler sonography, which was performed at three fixed times a day, the maternal blood pressure was examined each time. Outcome parameters were resistance index (RI), pulsatility index (PI) and the maximum velocity (V (max)) of the A. umbilicalis, A. cerebri media and the Aa. uterinae as well as the maternal blood pressure.

There were no significant differences for the RI, PI and V (max) of the Aa. uterinae for the whole collective, nor for the subgroups of maternal hypertonia, preeclampsia, notching and fetal growth restriction (IUGR). There were also no significant diurnal variations of the Doppler parameters for the fetal vessels. In particular, there were no differences in the measured Doppler parameters in comparison to the collective with unremarkable gravidity. In some subgroups statistical significance could be achieved, but due to the minor variations, no clinical importance has to be considered.

A circadian rhythm of the Doppler parameters could not be confirmed in the examined collective. The time of the applied Doppler sonography on physiological conditions might represent a factor which does not affect the validity of the Doppler sonographic results. As a consequence a single Doppler examination at a freely chosen time seems to be sufficient to obtain a correct assessment of fetal and maternal blood perfusion. Further studies on larger collectives are necessary to evaluate the clinical importance of a possible circadian rhythm, especially in fetuses with pathological Doppler values.