A simple method of internal tocography

A Review of Signal Processing Techniques for Non-Invasive Fetal Electrocardiography

Fetal electrocardiography (fECG) is a promising alternative to cardiotocography continuous fetal monitoring. Robust extraction of the fetal signal from the abdominal mixture of maternal and fetal electrocardiograms presents the greatest challenge to effective fECG monitoring. This is mainly due to the low amplitude of the fetal versus maternal electrocardiogram and to the non-stationarity of the recorded signals. In this review, we highlight key developments in advanced signal processing algorithms for non-invasive fECG extraction and the available open access resources (databases and source code). In particular, we highlight the advantages and limitations of these algorithms as well as key parameters that must be set to ensure their optimal performance. Improving or combining the current or developing new advanced signal processing methods may enable morphological analysis of the fetal electrocardiogram, which today is only possible using the invasive scalp electrocardiography method.

Standards in fetal monitoring--practical requirements for uterine activity measurement and recording

External monitoring of uterine contractility in human labour can record contraction frequency accurately, but cannot determine true intra-uterine pressure reliably. It is therefore suitable for use in spontaneous labour where there is a need for a marker of contractions to aid in continuous fetal heart rate pattern interpretation. Intra-uterine pressure measurement can provide quantitative information more reliably over intervals of 10-60 minutes. Although active pressure values for individual contractions can vary by up to 50% when measured simultaneously by two or more intra-uterine catheters/transducers, this variation is not systematic and cumulative measures vary by less than 5%. The measurement of baseline tone is affected by variables not related to uterine activity and should therefore be excluded when quantitative measures are made.

Measurement of uterine activity in labour--clinical aspects

Intra-uterine pressure measurement remains the most objective way of measuring uterine activity in labour, and in this respect is superior to clinical assessment or external tocography. However there is little evidence to show that improving the assessment of uterine activity in labour is associated with an improvement in the outcome of labour for mother or fetus. It seems logical that use of intra-uterine pressure monitoring will provide additional safety in women with a scarred uterus, breech presentation, high parity, or apparent failure of response to induction or augmentation of labour with the usual dose rates of oxytocics, but this has not been established by appropriately sized clinical trials. Further research to establish the role of uterine activity measurement in labour is urgently needed.

The accuracy of catheter-tip pressure transducers for the measurement of intrauterine pressure in labour

OBJECTIVE

To assess the reliability of intrauterine pressure measurements in labour with transducer tipped catheters.

DESIGN

Prospective clinical study.

SETTING

Delivery ward, National University Hospital, Singapore.

SUBJECTS

20 women admitted in early labour were randomly allocated to two groups.

INTERVENTIONS

Women in the first group had two catheters that had been tied together introduced transcervically into the same amniotic fluid pocket. The second group had two catheters introduced in different directions so that each catheter tip was in a different pocket of amniotic fluid.

MAIN OUTCOME MEASURE

The contraction to contraction pressure difference recorded by the two catheters in the same uterus. In addition, the cumulative uterine active pressure generated by one catheter was compared with that of the other.

RESULTS

There were differences in peak pressure of up to 4-5.3 kPa (30-40 mmHg) during some contractions. The difference in pressure recordings between the two catheters could not be explained by effects of loculation of amniotic fluid. However, the pressures recorded were not systematically higher in one catheter than in the other. Cumulative uterine activity was very similar when assessed by each catheter in the same uterus.

CONCLUSION

Intrauterine pressure measurements using transducer tipped catheters provide reliable information on the cumulative pressure wherever the catheter tip was sited in the uterus, but there are variations in pressures recorded during individual contractions.

Intrauterine manometry: reapplication of an old concept

Electronic fetal heart rate and uterine activity monitoring during labor requires expensive equipment and a source of electricity. However, it is not available to most of the women in the world. Intrauterine manometry provides a method which can be employed in underdeveloped settings to assess uterine contractions and to time auscultation. The vertical column of fluid in a standard intrauterine pressure catheter (IUPC) correlated well (R = 0.93) with the intrauterine pressure measurements obtained by a standard IUPC/pressure transducer system. Intrauterine manometry provides an alternative measure of uterine tone which may be employed in underdeveloped areas.

The endocrinology of parturition in the human

Current evidence suggests that oestrogens, progesterone, relaxin, the prostaglandins, and oxytocin are all hormones concerned to a major degree with the onset and maintenance of parturition. Oestrogens, relaxin, and the prostaglandins are particularly involved with cervical ripening, while prostaglandins, progesterone and oxytocin are more involved in regulating myometrial contractility. Catecholamines may also have some regulatory function in relation to uterine contractions. Progesterone dominance during pregnancy is associated with a firm closed cervix, few myometrial gap junctions, low calcium levels in the cells, and a quiescent myometrium. At term, a change in the oestrogen/progesterone balance favours cervical ripening and increased uterine activity. Of particular importance at the level of the muscle cell are changes in the number of oxytocin receptors; a complex interaction between cAMP and phosphoinositide metabolism governs the intracellular level of calcium, thus regulating contractile activity.

The effect of parity on uterine activity in labour

Uterine activity was studied in 40 multiparous Singapore women of Chinese origin who were in normal labour and had a normal delivery. A catheter tip pressure transducer coupled with a uterine activity integrator was used to quantify uterine activity. Normal labour progress was defined as labour progressing within 2 h to the right of a line drawn on the partogram at 1 cm/h in the active phase of labour. A wide range of activity was observed. The median level of uterine activity rose from 815 kPas/15 min at 3 cm dilatation to 1731 kPas/15 min at 9 cm dilatation with an overall median level of 1130 kPas/15 min. The 10th centile value rose from 430 kPas/15 min at 3 cm dilatation to 923 kPas/15 min at 9 cm dilatation. Profiles of dilatation-specific activity values were constructed. These values were significantly lower than in a comparative group of nulliparous patients. The parous uterus requires to expend significantly less effort to effect normal vaginal delivery than its nulliparous counterpart.

Strain uterography in labour

Multi-strain measurements of uterine contractions were made on 36 women at 36 to 42 weeks of pregnancy. The tracings obtained supported the existence of one dominant pacemaker area in the fundal region of the uterus and indicated that the contractile wave travelled in a downward direction with an average speed of 6 cm/second. The analysis of all normal labours showed that strains of the longitudinal muscle fibres changed from extension in the fundal region of the uterus to compression in its lower part, through a local zero strain in a narrow zone below the umbilicus. Intensity of the uterine contractions reached 6 per cent in extension and -2 per cent in compression. Information about the number of peak contractions, the frequenty of contractions and the tonus of the myometrium during relaxation are of importance in the evaluation of uterine dysfunction.