After application, the electrodes were connected to the Monica AN24 monitoring device which was attached to the abdominal wall with an elastic band to prevent it from moving and to ensure a similar position across all of the studies. The skin was washed with soap and water if the participant had recently used skin ointment. Before application, the skin was lightly abraded to remove superficial dry squamous cells which could reduce electrode impedance. The fifth electrode was placed 5 cm lateral to the electrode on the right side. For the late gestation recordings (34-38 weeks GA), four electrodes were placed on the anterior maternal abdomen, one 5 cm above the umbilicus, one just above the pubic hairline, and the other two laterally, with one 10 cm to the right and the other 5 cm to the left of the umbilicus. Recordings were carried out in quiet rooms between 08h00 and 16h00 on weekdays with participants lying at a 15° right or left lateral tilt. ![]() Ethical approval was obtained from the Health Research Ethics Committee of Stellenbosch University (Ethics approval number: N06/10/210). All participants had an ultrasound examination to confirm the gestational age. All assessments were done at Tygerberg Hospital. Participants from the clinical site in South Africa were recruited at a local community health centre. Stillbirth was one of the primary outcomes. Recruitment included low and high risk pregnancies, with a wide range of exposures to alcohol, nicotine, cannabis and methamphetamine. The Safe Passage Study was designed to investigate the role of prenatal alcohol exposure (PAE) in 12,000 pregnancies. Here we describe several unique patterns which have appeared in this data set and demonstrate its association with uterine activity at 34 to 38 weeks gestation. The transabdominal recording of the fetal heart rate was feasible as early as 20-24 weeks gestation. More information on the MHR is emerging, as part of the data collected in the Safe Passage Study, where fetal heart rate patterns and fetal movements were recorded at different gestational ages. In addition, it records electrical impulses from the uterus to illustrate contraction patterns resembling what is observed with direct recordings of intrauterine pressure. The fetal (f) ECG signal quality is significantly better during the first stage of labor in comparison to Doppler cardiotocography and the monitor can provide a continuous printout of the MHR with less MHR/FHR ambiguity when compared to the cardiotocograph. The Monica AN24™ (Monica Health Care, Nottingham, UK) uses the raw data obtained from five electrodes placed on the anterior abdominal wall of the mother. Reports on incidental monitoring of the MHR by scalp electrodes or ultrasound transducers provide little information on different MHR patterns. There is also little information about the periodic effects of uterine activity on the MHR prior to the onset of labour. There is a paucity of literature regarding maternal heart rate (MHR) under resting conditions during pregnancy, before the onset of labour. Another developing field of interest is assessment of heart rate variability (HRV) as a biomarker for autonomic nervous system (ANS) function. As heart rate is one of the determinants of cardiac output, it is essential to know more about the significance of ranges of maternal heart rates in pregnancy. Importantly, cardiac disease is becoming one of the leading cause of maternal death in developed countries because of increased maternal age and extended survival of patients with congenital heart disease. Poor maternal cardiac function is associated with reduced fetal growth as reflected by reduced birth weight and preterm delivery, with reduced cardiac output and maternal cyanosis suggested as underlying mechanisms.
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