Study: ECGs for Maternal and Fetal Heart Rate Evaluations

Using a fetomaternal electrocardiogram (ECG, a noninvasive way to measure electrical changes in the heart) to monitor the fetal heart rate in the last two months of a high-risk pregnancy can help determine whether the unborn foal is healthy, according to Christina Nagel, MSc, PhD, at the Graf Lehndorff Institute for Equine Science in Neustadt, Germany. Using that technology, Nagel et al. recently completed a study in which they examined heart rate and heart rate variability in the pregnant mare and her fetus.

Fetomaternal ECGs

In her study, Nagel evaluated the heart rates of pregnant mares and their fetuses using a fetomaternal ECG.

"In contrast to other methods (of monitoring the pregnancy, such as transrectal palpation or transabdominal ultrasonography), which show only a short period, the fetal ECG can be used for long-term monitoring so that it is possible to get a good evaluation of the fetal well-being," Nagel explained.

Fetomaternal ECGs were first evaluated in 2010 as a fetal monitoring tool. In the current study Nagel et al. aimed to determine the normal values in heart rate (HR) and heart rate variability (HRV, the slight changes in heart rate from beat to beat) of the pregnant mare and her fetus, and to detect physiological changes during ongoing gestation.

Nagel and her team monitored seven Warmblood broodmares (aged 5 to 20 years) and their fetuses during the last two months of pregnancy and parturition (labor) with ECG equipment to gain a better understanding of how the two cardiovascular systems function together.

Key findings in the study included:

  • Overall, there was no significant increase in the mares' heart rates throughout gestation;
  • The mares' heart rates increased during the last month of pregnancy;
  • Conversely, the heart of most fetuses decreased in the last month from about 110 beats per minute (BPM) and to around 80 BPM; and
  • During delivery some foals' heart rates dropped to 50 BPM during delivery (which could explain why prolonged deliveries are so dangerous to foals, the researchers noted).

"In the mare, the increase in heart rate is a sign of increased demands of the cardiac system, because of the ongoing pregnancy and the growing foal," said Nagel. The decrease in the fetal heart rate could be due to the maturing of the foal's autonomous nervous system in preparation for life outside the womb, she added.

Nagel believes these baseline values could be useful for detecting fetal or maternal stress during pregnancy, as large variations in HR or HRV in either the mare or the fetus could be indicative of a problem.

"I don't think it is necessary to do the fetomaternal ECG in normal pregnancies, but in high-risk pregnancies it should be used," Nagel suggested.

Many equine practices have the ECG equipment needed to provide long-term monitoring. However, specialized training is needed to read an ECG report, so work closely with a veterinarian if a mare has a high-risk pregnancy and requires monitoring.

Nagel recommended that veterinarians monitor high-risk pregnancies daily for a minimum of 30 minutes, but 24-hour ECGs are also possible for extreme cases.

Although fetomaternal ECG can help assess the health of the foal, it cannot be used to predict foaling, she added.

The study, "Heart rate and heart rate variability in the pregnant mare and its foetus," was published in March in the journal Reproduction in Domestic Animals. The abstract is available on PubMed.

About the Author

Marie Rosenthal, MS

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