Fetal Heart Monitor
FETAL HEART RATE MONITORING
by Dr. Marie O. Andal, OB-GYN
Intrapartum (during labor) fetal health surveillance is very important to detect potential fetal decompensation and be able to make interventions early enough to prevent fetal injury or death The fetal brain is the primary organ of interest but is not currently accessible for evaluation antenatally. It is well-known that characteristic fetal heart rate (FHR) changes often come before any brain injury. Currently, the most valuable non-invasive method of intrapartum evaluation is FHR monitoring. Finding of normal FHR can reassure the parturient and the Obstetrician that it is safe to continue labor if no other problems are present.
In our setting, there are two types of monitoring done during labor. The first type is through intermittent auscultation (IA) using either a stethoscope or a device called a Doppler transducer. Monitoring is done by periodically listening to the fetal heartbeat through the maternal abdomen. This is recommended to all low- risk women in established first stage of labor. The IA of the FHR is carried out after a contraction for at least 1 minute, at least every 15 minutes and must be recorded as a single rate. Accelerations and decelerations must be recorded if heard. The maternal heart rate must always be differentiated from the fetal heart rate.
The other type is electronic fetal monitoring (EFM). EFM uses a special equipment to measure the response of the baby’s heart rate to the contractions of the uterus. EFM can be external, internal or both. The external method of EFM or Cardiotocography (CTG) is the focus of this article. With CTG, a pair of belts is wrapped around the maternal abdomen. One belt uses Doppler to detect the fetal heart rate. The other belt measures the length of contractions and the time between them. CTG continuously records the heartbeat of the fetus and contractions of the mother’s uterus during labor. During the monitoring, a fetal heart tracing is produced which can be interpreted and reviewed by the attending obstetrician. CTG is not routinely recommended for low-risk women in established labor. When is electronic fetal monitoring recommended? Table 1 shows the antenatal and intrapartum risk factors that should prompt the obstetrician to advise the use of continuous electronic fetal monitoring.
The FHR tracing obtained is interpreted based on the Three-Tier. FHR Classification System. Category 1 FHR tracings are considered normal, and no specific action is required. With this tracing, one is virtually certain that the fetus is not suffering from hypoxia, acidemia or other causes of distress. Category 2 tracings are considered indeterminate.
This category requires evaluation and surveillance and possibly other tests to ensure fetal well-being. Category 3 tracings are considered abnormal and require prompt evaluation. Detection of an abnormal FHR pattern (Category III) is an indication for abdominal delivery or cesarean section (CS) (Level 1, Grade A). The presence of 3 consecutive Category II abnormal FHR patterns, despite resuscitative measures (providing oxygen to the pregnant woman, changing woman’s position, discontinuing labor stimulation, or treating maternal hypotension), is an indication for CS. If an emergency CS is warranted for an abnormal FHR pattern or acute fetal compromise, the optimal decision-to-delivery interval should be ideally within 30 minutes.
Different studies support the need for immediate CS when an abnormal FHR is identified. Overall, there was a significant trend towards neonatal acidosis (pH < 7.2) and 5-minute Apgar score of <7 in cases with abnormal FHR patterns. Ominous patterns were associated with increased incidence of neurological morbidity ((neonatal encephalopathy) (Odds ratio [OR] 2.9, 95% confidence interval [CI] 1.07-7.77). Occurrence of multiple late decelerations was associated with an increase OR of cerebral palsy (OR 3.9,95% CI 1.7-9.3).
I came from a training institution where the idea set up for fetal heart rate monitoring is always being emphasized. Since the start of my practice here in the locality, the only FHR monitoring used (for low risk and high-risk patients at that) is only IA. Now, it is of great relief that the Palawan MMG Multipurpose Cooperative Hospital has already acquired a Digital Cardiotocogram (CTG7 Fetal/Maternal Monitor). Now, high-risk patients in labor whom continuous electronic fetal heart rate monitoring is recommended, can be monitored appropriately. With proper use of the cardiotocogram and right interpretation of fetal tracings, timely intervention come in play and on the other hand, unnecessary measures are avoided. Overall, the goal is to achieve a good outcome: to deliver a healthy baby and have a happy mommy.
REFERENCES:
- Macones GA, Hankins GD et al. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation and research guidelines. J Obstet Gynecol Neonatal Nurs 2009; 38 (1): 4- 5.
- ACOG. ACOG technical bulletin. Fetal heart rate patterns: monitoring, interpretation, and management. Int J Obstet Gynecol 1995; 51: 65-74.
- POGS. Clinical Practice Guidelines on Cesarean Section, 2nd Edition, November 2012. 61-64