Author: Tamerou Asrat, M.D.
Objective: Upon the completion of this CNE article, the reader will be able to
- Discuss the importance of appropriate follow-up regarding an equivocal fetal monitor strip that is obtained for reasons that are outside the setting of antepartum testing.
- Describe the differences between “variability” and fetal heart rate “accelerations”.
- Explain the importance of obtaining an umbilical artery cord blood sample and a placental evaluation in cases that involve low Apgar scores or abnormal fetal heart rate tracings.
- Define the criteria that are needed in order to say that an acute intrapartum hypoxic event occurred that was sufficient to cause cerebral palsy.
A 24-year-old female Gravida 2 Para 1 with an expected date of delivery of 4-27-98, presented to labor and delivery on 4-24-98 at a gestational age of 39 4/7 weeks with a complaint of cramping. Her prenatal course was uncomplicated and uneventful. She was placed on a monitor and was noted to have contractions that were occurring approximately every 3 to 5 minutes. Her vital signs were normal and she had no other complaints. Her vaginal exam was as follows: fingertip dilation, 50% effaced, minus 1 station, cephalic presentation. The initial strip is as follows:
She was placed on her left side and observed for possible early labor. Continuous fetal heart rate monitoring occurred and the tracing stayed similar to that seen in strip #1. Strips #2 and #3 occurred approximately 1 hour and 2 hours, respectively, into the observation time. Her contractions during this time period spaced out somewhat and were occurring approximately every 5 to 8 minutes apart.
Following what was seen in strip #3, she was monitored for an additional 5 hours. On re-examination, no cervical change occurred. In addition, her contractions completely spaced out and she no longer felt any cramping. Therefore, her prenatal care provider was contacted and the decision was made to discharge the patient home. She was given instructions to follow-up with her next scheduled appointment, and she was given information on how to perform daily fetal kick counts. In addition, she was told to return to labor and delivery for any vaginal leakage of fluid, redevelopment of contractions every 5 minutes apart or closer, vaginal bleeding, or decrease in fetal movement. Strips #4 and #5 depict what was seen just prior to her discharge from the hospital. In total, she was monitored for approximately 7 hours and the entire tracing was similar to those seen in strips #1, #4, and #5. The only variations seen on the strip for the entire monitoring period were those seen on strips #2 and #3.
At approximately noon, two days later, the patient called labor and delivery with a complaint of decreased fetal movement. That morning when she woke up, she had taken her other child to preschool, and then returned home. While at home, she noticed that there was very little fetal movement, if any. She denied any other complaints or symptoms. She also stated that she was following the daily fetal movement counts and they were within the expected range on the day of her prior discharge and the following day (the day prior to this call). She then was instructed to come into labor and delivery for evaluation. On arrival, the patient stated that she again was feeling cramping that was increasing in intensity, similar to the labor she experienced with her first child. Tracings # 6 and #7 show what was initially seen after her arrival.
Based on the findings, the patient was immediately admitted to the hospital. Her vital signs were all within normal limits. On vaginal examination, her cervix was found to be 3 cm dilated and 80% effaced, with the presenting part at zero station. No vaginal bleeding was identified. She was placed on her left side, and an intravenous line was inserted. She was quickly hydrated and oxygen at 8 liters by mask was instituted. Because of no improvement in the tracing, she was informed of the findings and consented for an emergency cesarean section that was accomplished shortly thereafter (approximately an hour and 15 minutes after arrival). At the delivery, thick meconium was encountered. The baby was a 3,127 gram male with Apgar scores of 2 at 1 minute, 5 at 5 minutes, and 7 at 10 minutes. The newborn was taken to the neonatal intensive care unit for further management. An umbilical artery cord blood gas was obtained and the results were as follows:
pH = 7.09
PCO2 = 67
PO2 = 15
HCO3 = 16 (bicarbonate)
BD = 13 (base deficit of 13 / this value is often recorded as base excess or BE, but the number will be the negative, i.e. BE = –13)
The neonate showed poor tone throughout the first three days of life and developed seizures, the first of which occurred within 2 hours of birth. An EEG was obtained and was read as significantly abnormal. The child eventually went on to demonstrate major neurologic impairment with spastic quadriplegia and microcephaly. The placenta was sent to pathology and was found to have several infarcts ranging from 1 to 2 centimeters in size, some of which were old in appearance and others that were more recent in onset. Also seen was evidence of vascular thrombosis and micro-calcifications.
This case demonstrates the importance of remembering that the management of a fetal heart rate strip in a patient who ultimately goes home (prior to delivery) is different than a patient who is admitted and will ultimately deliver. When a patient is admitted to be delivered, an occasional fetal heart rate deceleration is a common finding and is usually of no significance unless the decelerations become repetitive and other changes are noted in the overall strip. However, obstetrical healthcare providers need to remember that any tracing performed in the antepartum period (one that is run on a patient who goes home prior to delivery), is equivalent to a non-stress test (NST). When a pregnant patient has a high-risk condition such as hypertension or diabetes, or develops an antepartum problem such as decreased fetal movement, they are often sent for antepartum testing, which may involve an NST, or a contraction stress test (CST), or a biophysical profile (BPP), or a modified biophysical profile (MBPP). When a patient undergoes one of these tests, she is usually followed-up based on a specific protocol for the test that was performed, in relation to the result of the test. Therefore, when a patient presents for the purpose of having an antepartum fetal surveillance test, more than likely, a protocol will be followed and the appropriate follow-up test will be scheduled.
When a patient presents for a different reason (such as cramping, or vaginal discharge, or a headache in a patient with normal blood pressure, etc), the healthcare system may not view the fetal heart monitor tracing in the same fashion as an "antepartum fetal surveillance" test. However, it is very important to recognize that the strip needs to be handled in a similar manner. Using a hypothetical, if a patient, with a history of chronic hypertension that is under good control, presents for a scheduled NST and the tracing is completely normal – read as reactive – the patient will often be rescheduled for another test that will occur sometime in the next few days to a week (based on the type of test performed and its given protocol). If the tracing or NST in this well-controlled hypertensive patient is reactive but equivocal (meaning that a deceleration occurred), the patient might have a more in-depth evaluation (such as a BPP or CST) or may be rescheduled to come back the following day for another test (again, depending on the given protocol for the institution). Similarly, some patients are sent for antepartum testing and the indication may not require a specific re-schedule. A good example for this is a complaint of decreased fetal movement in an otherwise low-risk patient. If the NST is reactive, the patient is often rescheduled as "clinically indicated" (meaning that no definite future appointment was made). On the other hand, if the test is reactive but equivocal (in this hypothetical patient with decreased fetal movement), the patient will have a more in-depth back up test performed or be asked to repeat the test the following day.
It is extremely important to recognize that this same type of "follow-up" protocol should occur when a patient (who is not on an antepartum testing scheme) presents to labor and delivery for a totally different reason but has fetal monitoring performed.
The tracing from the original visit to labor and delivery in the "case presentation" in this article is very reactive because of the numerous fetal heart rate "accelerations" that were seen. However, it is also equivocal because of the two decelerations that were picked up and depicted in
strips #2 and #3. Because the overall tracing was very reassuring, the patient was not beyond her expected delivery date, and she was not in labor, it was very appropriate to allow her to go home. However, because of the equivocal finding, she should have been scheduled to return the next day for a follow up NST.
It is difficult to say whether or not the poor outcome seen in this case could have been prevented. One potential scenario could be that a repeat NST performed the following day would have been reactive without any decelerations and she would be followed as "clinically indicated" – only to have some unforeseen acute event occur on the night before or the morning of her second admission. Whereas, another scenario might have been that a repeat NST the following day would have had further decelerations that prompted induction or possibly an ultrasound to check the amniotic fluid volume (and if abnormally low, again induction), both resulting in a delivery before any damage occurred. Based on the placental evaluation, it appears that there was a placental abnormality that is consistent with ongoing uteroplacental insufficiency (infarcts of recent onset). In addition, the umbilical artery cord blood gas is not consistent with an acute event that was occurring at the time of delivery, nor is the strip from the second labor and delivery visit. However, because a follow-up test was not scheduled or performed, we cannot say for certain which situation occurred.
An umbilical artery cord blood gas, that is indicative of a severe acute ongoing hypoxic event, will usually have a very low pH (one that is below 7.0). In addition, the bicarbonate will usually be lower than what was seen (often less than 14) and the base deficit will most often be higher (12 or above) (see ref. 1). The umbilical artery cord blood gas in this case is abnormal but is only consistent with a mild to moderate acidosis (with a pH of 7.09) and it has a mixed respiratory / metabolic component because the pCO2 is also slightly elevated (normal range of about 35 to 55 for one standard deviation) (see ref. 4).
The fetal monitor tracing from the second visit to labor and delivery (strips #6 and #7) is clearly abnormal. There is absence of variability and the baseline appears to wander or is unstable. This is most consistent with a pre-existing injury to the brain (see ref. 7 & 9). When analyzing a fetal monitor tracing, the most important aspect is the variability (or squiggliness of the line). The variability of a fetal monitor tracing, when present, tells you that the "push" / "pull" effect of the central nervous system is working. The sympathetic nervous system tries to increase the heart rate, whereas the parasympathetic nervous system tries to slow it down. In a microscopic view, this increase / decrease effect is depicted as variability on the fetal monitor tracing. Thus normal variability is indicative of a central nervous system that is not significantly hypoxic or acidotic at the time (see ref. 7 & 10).
Fetal heart rate "accelerations" are different. By definition, an "acceleration" (in a pregnancy at or beyond 32 weeks gestation) is an increase in the heart rate that peaks at least 15 beats per minute above the baseline and lasts for at least 15 seconds from the time the heart rate leaves the baseline to when it returns to the baseline (see ref. 2). The majority of these accelerations are associated with fetal movement (verified by simultaneous ultrasound evaluation of the fetus in conjunction with fetal monitoring) (see ref. 8). This finding makes good physiologic sense. If a person were to record their pulse in the resting state and then retake it immediately after running 10 to 15 feet, they would most likely notice a slight increase in their heart rate related to the small burst of activity. This phenomenon is also seen in the fetus in relation to fetal movement. The presence of accelerations on a fetal monitor tracing is a very reassuring sign. The absence of accelerations in a laboring patient, however, is not necessarily ominous, especially if there is variability.
The term "reactive" is used based on whether or not a specified number of fetal heart rate "accelerations" have occurred in a specified time period. Numerous articles have been published on this topic with slight variations (see ref. 7). Most institutions that perform antepartum fetal surveillance and utilize the NST, as one of their tests, will define the number of accelerations that need to be seen in a specified time period in order for the strip to be called "reactive". If there are no areas on the strip that meet the defined requirement of accelerations, then the tracing will be called non-reactive. Therefore, the terms reactive and non-reactive pertain to "accelerations" not the variability.
Strip #5 would be considered reactive (with 3 to 4 accelerations, as defined above, in a 7-minute window), and as a second interpretation, the variability is moderate or normal.
As a side discussion, one might question the length of time from when the patient presented the second time to labor and delivery and her ultimate delivery by cesarean section (an hour and 15 minutes). Cesarean sections are usually described as "scheduled" versus "emergency". A "scheduled" cesarean section is usually one that is placed on an operating room schedule hours or days in advance for a non-acute pregnant patient. An "emergency" cesarean section is all others. Unfortunately, "emergency" cesarean sections often fall under a time scrutiny – the "30-minute rule". The joint statement from the American College of Obstetrics and Gynecology (ACOG) and the American Academy of Pediatrics (AAP) states that not all emergency cesarean sections are subject to the 30-minute rule (see ref. 6). To perform a cesarean section under the 30-minute rule cuts corners on normal patient and physician prep time and can increase the risk of maternal hemorrhage and infection. Therefore, it should only be used under certain circumstances. Thus, a patient who arrives at term with ruptured membranes, not in labor, but is a footling breech, does not have to be delivered within 30 minutes.
In an abbreviated synopsis, the 30-minute rule is as follows: "All hospitals offering labor and delivery services should be equipped to perform emergency cesarean delivery. The required personnel including nurses, obstetric attendants, anesthesia personnel, and neonatal resuscitation team members should be readily available. The consensus is that these hospitals (when presented with certain obstetrical emergencies) should have the capability to begin the incision of the cesarean section within 30 minutes of the decision (decision to incision)" (see ref. 6). These "30-minute rule" cesarean sections are often called "stat" or "crash" c-sections by some institutions to differentiate them from a non-30-minute rule emergency cesarean section. According to the joint statement from ACOG and the AAP, the term readily available "should be defined by each institution within the context of its resources and geographical location" (see ref. 6). The delivery for this case presentation would not fall under the 30-minute rule; however, observing this type of tracing for several hours would also probably not be appropriate.
Though the outcome in the case presentation is poor, the importance of obtaining an umbilical artery cord blood gas and placental evaluation cannot be understated. The tracing that is depicted in
strips #6 and #7, could also be seen in a fetus that has suffered a major neurologic injury due to other causes such as an inutero umbilical cord accident, a TORCH infection (toxoplasmosis, rubella, cytomegalovirus, herpes), a significant fetal-to-maternal hemorrhage that produces severe fetal anemia, or a spontaneous stroke or CNS bleed from a ruptured arteriovenous malformation (AVM) or aneurysm, etc. A placental evaluation and the umbilical artery cord blood gas values can often help in the analysis of these possibilities.
It is crucial to recognize that the American College of Obstetrics and Gynecology and the American Academy of Pediatrics have defined the criteria that are needed in order to say that an "intrapartum" hypoxic event occurred that produced the cerebral palsy seen in the child. These definitions come from a review of numerous publications on the topic as analyzed by the International Cerebral Palsy Task Force (see ref. 3). To say that an acute "intrapartum" event occurred, all four criteria are needed (see ref. 1):
- Evidence of metabolic acidosis in the fetal umbilical cord arterial blood obtained at delivery (pH < 7.0 with a base deficit > 12 mmol/L)
- Early onset of severe or moderate neonatal encephalopathy in infants born at 34 or more weeks of gestation
- Cerebral palsy of the spastic quadriplegic or dyskinetic type
- Exclusion of other identifiable etiologies, such as trauma, coagulation disorders, infectious conditions, or genetic disorders
The following five criteria are suggestive of an intrapartum event or one that occurred within 48 hours, but are nonspecific to asphyxial insults (see ref. 1):
- A sentinel hypoxic event occurring immediately before or during labor
- A sudden and sustained fetal bradycardia or the absence of fetal heart rate variability in the presence of persistent late, or variable decelerations, usually after a hypoxic sentinel event when the pattern was previously normal
- Apgar scores of 0 to 3 beyond 5 minutes
- Onset of multisystem involvement within 72 hours of birth
- Early imaging study showing evidence of an acute nonfocal cerebral abnormality
It is important to understand that severe acute intrauterine hypoxia is a global event. This means that all organs of the fetus are subjected to the same lack of oxygen. Therefore, when the liver or the kidneys are subjected, one will often find elevated liver function tests or renal function tests, respectfully. The liver and the kidneys can regenerate, however. When the brain is subjected to acute severe hypoxia, it is also affected in a global sense. Research has shown that acute intrauterine hypoxic events severe enough to cause permanent brain injury will produce spastic quadriplegia or dyskinetic cerebral palsy. Spastic diplegia, hemiplegic cerebral palsy, and mental retardation without any motor component are not global and are very unlikely to be the result of an intrauterine hypoxic event (see ref. 3 & 5).
In this case presentation we have spastic quadriplegia, but we only have 3 of the top four requirements. The arterial cord blood gas does not meet the conditions. Likewise, in the five suggestive criteria, we do not have a sentinel event that occurs once she arrives on the day she delivers and the Apgar scores are not 0 to 3 beyond 5 minutes. We do have a fetal heart rate strip with 2 decelerations seen two days prior to the delivery date, but the overall tracing that day was reassuring followed by a change to abnormal on the day she is delivered. Therefore, the sentinel event in this case most likely occurred between her first and second hospital visits.
References or Suggested Reading:
- ACOG. Inappropriate Use of the Terms Fetal Distress and Birth Asphyxia. American College of Obstetrics and Gynecology Committee Opinion #326 December 2005.
- ACOG. Intrapartum Fetal Heart Rate Monitoring: Nomenclature, Interpretation, and General Management Principles. American College of Obstetrics and Gynecology Practice Bulletin #106 July 2009 – Reaffirmed 2013.
- ACOG / AAP. Neonatal Encephalopathy and Neurologic Outcome 2nd Edition. American College of Obstetrics and Gynecology and American Academy of Pediatrics 2014.
- Helwig JT, Parer JT, Kilpatrick SJ, Laros RK. Umbilical cord blood acid-base state: What is normal? Am J Obstet Gynecol. 1996,174:1807-14.
- Nelson KB, Grether JK. Potentially asphyxiating conditions and spastic cerebral palsy in infants of normal birth weight. Am J Obstet Gynecol. 1998,179:507-13.
- ACOG / AAP. Guidelines for Perinatal Care 7th Edition. American College of Obstetrics and Gynecology and American Academy of Pediatrics. October 2012 Pages 177-180.
- Freeman RK, Garite TJ, Nageotte MP, Miller LA. Fetal Heart Rate Monitoring 4rd Edition. Lippincott Williams and Wilkins. Philadelphia, PA. 2013.
- Rabinowitz R, Persitz E, Sadovsky E. The relation between fetal heart rate accelerations and fetal movements. Obstet Gynecol 1983,61:16-18.
- Cetrulo CL, Schifrin B. Fetal heart rate patterns preceding death in utero. Obstet Gynecol 1976,48:521-5.
- Parer JT. Handbook of Fetal Heart Rate Monitoring 2nd Edition. Saunders. Philadelphia, PA 1997. Pages 156-9.
- ACOG. Management of Intrapartum Fetal Heart Rate Tracings: American College of Obstetrics and Gynecology Practice Bulletin #116 November 2009 – Reaffirmed 2013.