The incidence of maternal artefact during intrapartum fetal heart rate monitoring.

OBJECTIVE

To determine the incidence of maternal heart rate artefact (MHRA) when monitoring fetal heart rate (FHR) in labour and to determine obstetrical factors associated with MHRA.

METHODS

In a prospective observational study, maternal and fetal heart rates were displayed simultaneously to document the superimposition of the maternal heart rate (MHR) on FHR tracings. All women in labour who were undergoing external fetal monitoring (EFM) at the Ottawa Hospital from October 2011 to March 2012 were eligible. Every episode of MHRA was documented and classified according to its clinical significance. Wilcoxon test, t tests, and chi-square tests were used to identify time-related differences and obstetrical factors (epidural analgesia, fetal presentation, multiple gestation, maternal BMI, umbilical cord arterial pH, five-minute Apgar scores) that were associated with a potential adverse outcome.

RESULTS

We assessed 1313 tracings with simultaneous displays of the MHR and FHR in labour. MHRA was present at least once in 721 tracings (55%). Of these tracings, 35 were classified as having one or more episodes that might have led to an adverse outcome (either false positive or false negative), giving an incidence of 2.7% of all women in labour. In 33 tracings, the MHRA masked an abnormal FHR tracing. In two tracings, the MHRA masked a normal FHR, which might have resulted in misinterpretation of the tracing (i.e., false positive), leading to unnecessary intervention.

CONCLUSION

The incidence of MHRA is higher than currently thought, and in more than 2% of women in labour may lead to adverse outcomes. We propose routine use of simultaneous maternal and FHR monitoring for women undergoing EFM, especially during the second stage of labour.