Nonlinear analysis of biomagnetic signals recorded from the umbilical artery in normal and pre-eclamptic pregnancies

Abstract

Objective: In this study we investigated the hemodynamics of the feto-placental circulation in normal and pre-eclamptic near term pregnancies using the biomagnetometer SQUID. Thirteen abnormal and 25 normal pregnancies were included in this study. Study design: The biomagnetic signals were analyzed using nonlinear analysis in order to differentiate these two types of pregnancies. Results: The application of nonlinear analysis reveal a clear saturation dimension value for pre-eclamptic and non-saturation for normal pregnancies. These findings were statistically significant and were correlated with fetal heart rate monitoring, pH and Apgar score: high biomagnetic cases (140–300 fT /√Hz) were related with normal patterns, pH>7.25 and Apgar >7, while low biomagnetic recordings (50–110 fT /√Hz) were connected with abnormal patterns, pH<7.25 and Apgar<7. Conclusions: It is suggested that the biomagnetic measurements with SQUID and the application of nonlinear analysis, is a promising procedure in assessing fetal health, especially in high risk pregnancies.

Introduction

The hemodynamics of the umbilical circulation have been the focus of intensive interest during the past decade because an increase of resistance in the flow velocity waveforms (FVW) from the umbilical artery is commonly associated with an increased risk for pre-eclampsia [1] and fetal growth retardation [2].

It is thought that this increased resistance of umbilical artery flow reflects histopathological changes in the uteroplacental and fetoplacental circulations [3] . Such arterial flow disturbances are currently investigated by Doppler ultrasound. However, the Doppler velocimetry in the fetal umbilical artery has been reported to be extremely variable, with a sensitivity ranging from 20% to 80% [4], and there is potential for further improvement.

In recent years an interesting development was the introduction of the biomagnetometer SQUID into clinical practice. SQUID, which stands for Superconducting Quantum Interference Device, is an investigating tool capable of measuring the exceedingly weak magnetic fields emitted by the living tissues. Magnetic fields are produced spontaneously by all living tissues as a consequence of the continuous ionic movements across the plasma membranes [5] . The higher the concentration of living cells in the test area the higher the biomagnetic fields produced and the higher the recorded activities. This technique has been used successfully for studying fetal heart [6], [7], brain activity [8], [9], hemodynamics of the umbilical artery [10], and more recently, in detecting breast and ovarian tumors [11], [12]. It is worth noting that biomagnetometry is a non-invasive and totally harmless procedure, since the instrument acts as a receiver and not as a transmitter.

Here we report on the potential value of the biomagnetometer SQUID and the use of nonlinear analysis in assessing the feto-placental circulation which is very important especially in high risk pregnancies.