History of fetal monitoring ROBERT
Sir Robert Walpole (1746)
ofourcurrentobstetricliterature treats the past with disdain, I have undertaken with enthusiasm the task of compiling a brief history of fetal monitoring. Our obstetric predecessors were probably no less intelligent than are current investigators, and they often held with passion their various concepts and theories. Their papers contained much philosophical discussion, not particularly because they lacked data but in part because of their new and challenging ideas. While new techniques are now described at an unabsorbable rate, the presentation of new obstetric concepts is rare. If it were possible to determine what young house officers must read, I would include high on any list J. II. DeLee’s Principles and Practice of Obstetrics. * It is a complete expression of DeLee’s ekperience and viewpoints as well as a thorough review of our obstetric heritage. Hopefully, this paper will express some of the enthusiasms and spirit found in older papers and texts regarding fetal monitoring. I have limited the discussion primarily to biophysical concepts and have, of necessity, ignored the important test of fetal well-being obtained through amniotic fluid analysis and maternal hormonal or enzymatic tests. BECAUSE
From the Defartment Sacramento Medical Dazk.
of Obstetrics and Gynecology, Center, University of Calijornia,
Reprint requests: Dr. Robert C. Good& Department of Obstetrics and Gynecology, 2315 Stockton Blvd., Rm. 3004, Sacramento, Caigornia 95817. *DeLep, J. B.: Principles 1913.
The C. V. Mosby
Auscultation Fetal heart tones. In Western medical literature, Mayor’ of Geneva (1818) is credited with being the first to report the presence of fetal heart tones (FHTs).’ Their presence was independently discovered and extensively publicized by the French nobleman Lejumeau, Viscount de Kergaradec,’ in 1821. Legends would have us believe that the former discovered the fetal heart rate (FHR) while applying his ear to the abdomen of a woman to hear the fetus move, and the latter by attempting to hear, with Laennec’s stethoscope, a fetus splash in its amniotic fluid. Kergaradec, a pupil of Laennec, apparently refused to acknowledge Mayor’s earlier description, a dispute which was stirred by regional rivalry.3 As noted by Gultekin-Zootzmann,” there were clearly predecessors of Kergaradec in auscultation of FHTs other than Mayor. However, Kergaradec was the first to attribute clinical importance to the auscultation of FHTs. Surprisingly, he did not practice obstetrics but mentioned in his publications several practical applications of FHT auscultation. These included diagnosis of pregnancy and of plural pregnancies and determination of the state of fetal health and the fetal position. His limited obstetric experience was indicated by his suggestion that FHT auscultation was useful in the diagnosis of ectopic pregnancies5 While physicians on the continent were slow to appreciate Kergaradec’s 1821 description of FHT auscultation, Kennedy’ of Dublin published within 12 years’ time a monumental monograph on auscultation of the fetal heart (Fig. 1). Kennedy was an industrious person, 323
Fig. 1. Title page of Kennedy’s Longo, Loma Linda Universiq .)
for he established the first g)-necologic unit in any hospital in 1835 in the Rotunda (some 20 years before Sims established a similar unit in New York). He published several textbooks and was later to be a serious rival of Simpson for leadership in British obstetrics.’ Kennedy’s stated purpose in writing his 1833 monograph was to convince his fellow accoucheurs of the value of Kergaradec’s technique of FHT auscultation. Several copies of Kennedy’s various books are still in circulation at the Lane Library (Stanford Medical Center), and their file suggests that they were popular with the late nineteenth-centur! San Francisco physician. Many of Kennedy’s textbooks were republished in New York City without recognition of’ their prior British publication, thus leading some writers to believe that he practiced in America. Although some of his views on the significance of fetal distress have not stood the test of time (such as those relative to uterine “flatus”) most of his clinical impressions regarding the significance of various FHR patterns appear compatible with current concepts. In his 1833 book, Kennedy commented upon “M. Merat’s”experiments with newborn rabbits. These studies suggested to Kennedv that, since newborn hearts
beat longer than adult hearts when excised, fetal hearts were more resistant to anoxia. Kennedy also recounted M. le Docteur Bodson’s description in the Academic Royale de Medecine of fetal distress (“sufferance of the fetus”) which stated that the most ominous FHR pattern was “slowness of its return when a contraction is passing on”-perhaps the first description of a late dcceleration FHR pattern. Kennedy noted the importance of the effects of fetal head compression and funis compression on FHR. He finished this discussion with accurate reflections upon the significance of mecoilium-stained fluid. Despite what was an accurate and widely disseminated 1833 clinical description of irltrapartum fetal distress by Kenned!, Winckel’ in 1884 to 1893 was usually cited in American textbooks as the pioneer and authority in relating FHR patterns to fetal distress.‘.I ’ It is interesting to speculate as to why Kennedy’s coilcepts were essentially lost to the t~~entieth-centltr~ American obstetric text. In part, it may have been due to the respect that American authors had for the (:erman writer (DeLee wrote many of his papers in German) or to our predecessors’ overwhelming interest in maternal welfare. or perhaps to their fear of advocating more obstetric interference. In 1910, it was estimated that more than 17,000 American women died during childbirth” and that only tuberculosis destroyed more young women than did pregnanq. Indeed, between the two World Wars, maternal mortality rates were higher in .4merica than in any other advanced nation, and these maternal deaths were the major subject of concern of our obstetric leaders. I” However. with the problem of maternal deaths largel) resolved in the 1950’s, obstetricians again turned to Kennedy’s concerns for the welfare of the human fetus and attempted to understand the significance of its heart rate patterns. Except for Kennedy’s monograph, the majority of early nineteenth-century discussions of auscultation in the obstetric literature were concerned with whether the gravid woman should be standing or supine fol FHT auscultation. or whether the i&rect (stethoscope) or direct (ear to abdomen) method was best, or even whether it was acceptable to examine the nude belly of a woman.“. I2 In 1849. Kilian”’ proposed the “stethoscopial indications for forceps oper-ation.” The forceps must be applied under favorable conditions without delay when the fetal heart tones diminish in frequency to less than 100 bpm or when they increase to 180 bpm, when the) lose their purity of tone, and when only one tone can be clearly heard.,’ In the second half of’ the nineteenth-century, Schwartz” recommended that the FHR be counted as often as possible during labor, both during and he-
tween contractions and suggested that fetal “asphyxic intoxication” modified FHR as did uterine contractions. Jaggard,‘” (1888) quoting Winckel, Runge, and others, stated that any elevation of maternal temperature was followed by a great disproportionate acceleration of the action of the fetal heart, and that chloroform was noted to depress fetal cardiac muscle (bradycardia) and that ergot when producing tetanic spasm of the uterine musculature, evoked FHR changes characteristic of “asphyxia.” Jaggard noted that fetal bradycardia associated with uterine contractions was especially apparent after rupture of the bag of waters and was related to fetal hypertension. Discussion also centered around whether fetal sex and weight influenced FHR. Budin,“j in 1886, reviewed the available literature and his own clinical experiences. Hc concluded that there was “no absolute relation between FHR and sex or weight of the infant” when the pregnancy was near term. In 1893, Wincke17 proposed definite criteria for fetal distress, mainly a FHR under 120 or over 160 bpm. By the late nineteenth century, the mechanisms of FHR bradycardia were fairly well understood in terms of our present knowledge. Schatz17 (1885) had provided detailed descriptions of umbilical cord compression and in 1870 Schwartz’” had described fetal bradycardia following compression of the fetal head. Fischer also credits Kehrer18 with an 1867 description of fetal bradycardia associated with head compression. When one recalls that recorders were not available to these early investigators, their observations become all the more remarkable. Nearly all of these late nineteenth-century reports ascribed the acute fetal bradycardia as “due to vagal activity.“” Seitz’” stressed in 1903 that no sharp delineation existed between pathologic and physiologic FHR deceleration during uterine contraction. However, he was perhaps the first to distinguish three stages (or types) of FHR deceleration. The first two were related to vagal activity (head or cord compression?) and the third to complete paralysis of all extracardiac nervous activity, (uteroplacental insufficiency?). In keeping with modern concepts, Seitz suggested that the FHR served as an indicator of fetal oxygenation. While Bumm, in his 1917 German textbook, depicted intrapartum FHR changes and their evaluation. this was not true of American obstetric textbooks.‘” In the same era. DeLeeS devoted almost as much discussion in his textbook to observation of in utero fetal breathing activity as to the FHR. Williams8 barely mentioned FHR, other than it confirmed a diagnosis of pregnancy. The in utero souffle. The fetal souffle (systolic murmur) was considered bv Schroede? to be due to
sounds originating within the fetal heart, associated with hypertrophy of the right ventricle. Virchow apparently attributed its occurrence to insufficiency or vegetation on the fetal tricuspid or mitral valves,” while Braun ascribed the sound to flow through the foramen ovale and Scanzoni considered the souffle to represent functional cardiac anomalies.‘;’ The Ju~ic souffle was first describecl by Kennedy’ (1833) and was later shown by Kehrer”’ to be due to compression of the umbilical cord. In a case where the cord was palpable between the fetal body and the wall of the uterus, he produced a funic souffle (systolic murmur) by compression of the umbilical cord with a stethoscope. Charrier’” (1878) suggested that the appearance of the funic souffle was a sign of impending asphyxia and an indication for termination of pregnancy. Wincke17 (1893) also claimed that cases in which the funic souffle was present during labor were a risk and that operative interference was indicated if it was accompanied by changes in fetal heart tones. However, Jaggard”’ (1888) reviewed the relevant literature and suggested that the funic souffle by itself was not an indication for termination of pregnancy or operative interference. William? in 1903 suggested that the funic souffle occurred in 15% of all pregnancies and was not a sign of any great importance. Sounds of fetal movements. Pajot*” studied the auditory sensations which were produced by active fetal mo\‘ements (bruit de choc foetal), which he considered were due to movement of fetal extremities.“’ .%hlfeld?” (1869) believed that it was impossible to hear the movement of fetal extremities and considered such sounds to be due to spasmodic contractions of the fetal diaphragm. Both writers considered such fetal movement sounds to be indicative of fetal movement and good health. Placental souffle. In utero sounds are a form of energy developed within the uterus in relationship to either the fetal heart or maternal pulsations of the placental bed. Both can be a potential source of monitoring. Braxton-Hicks, nearly 100 years ago, described the various sounds that occur from the placental souffle and their possible interpretation.*” There is no doubt that these placental sounds give a relative indication of blood flow and that such flow could be a useful indicator of perfusion of the placenta. Various techniques to convert these forms of energy into some sort of reliable diagnostic criteria have failed, although the in utero ballistocardiogram at times will demonstrate placental or fetal complexes. Fetal stethoscope (fetoscope). Prior to the twentieth century, obstetricians were divided on whether direct application of the ear to the belly of the pregnant women \vas better than either the biaural or monaural
Fig. 2. Hillis’s
report describing the fetoscope. (Reproduced with permission from Hillis. D. S.: J. A. M. A. 68:910. 1917. Copyright 1917, American Medical Association.)
stethoscope. They were also uncertain as to whether auscultation during or between uterine contractions provided the most information. A vaginal stethoscope (metroscope) designed by Nauche ( 1865) was applied within the “cervical cavity.” Jaggard’” stated that the instrument fell into disuse “on account of the alleged violence to the parts.” However, he cited Verardini (1878) of Bologna as using such an intravaginal
stethoscope \vithout complications and being successful in hearing FHT’s as early as the “twelfth week.” ‘I‘lre obstetric. head stethoscope (fetoscope) has an important place in .4merican obstetrics. Willis” de>crihed the first instrument in 1917 (Fig. 2) in a brief and concise pitptzl In 1922. DeLee” described an almost identical instrument. The early modeis of the instrument \ver‘c’ advertised by the manufacturer as the “DeI.er” stethoscope.” Auscultatory signs of fetal distress. Prior to the advent of fetal scalp sampling and elecrronic and ullrasonic monitoring, the intrapartum chnical criteria of fetal distress were based mostly upon criteria of Winckel’ ( lH!#). These included: ( I ) rachycardia (FHR of mo1.e than 160 bpm), (‘L) bradycardia (FHR of less than 100 bpm), (3) “irregularity” of FHR (never defined), (3) passage ol rneconium in the vertex presentation, illld (5) gross alteration of fetal movemenls (nevel- defined). Lund’” (194X) later emphasized the significance 01 tachl-cardia. A controlled study by Walker’“’ in 1959 suggested that these clinical criteria were of little predictive vahie. In 1965 Hellman~” suggesrrtl that “WY do not do much more with the complicatcd itistrum(~nts at hand than Laennec did with the 5tethoscopc in 1 X2 1.” ‘I‘hc cxperiencrs of Cox a’. “” in the 1950’s in Australia is representative of’ studies reported during that time period. The main conclusion was that a minimal increase in newborn morbidity and perinatal deaths occurred when only one of the clinical signs of fetal distress was ohser\etl on a single occasion. However, when these clinical signs were observed in combination or repetitively. thr morbidity and pcrinatal mortality rates were milch higher. Except for Walker’s”’ (1959) study in South Africa, there appear- to have been few efforts in that cm to study and evaluate objectively the clinical signs of f’etal distress. Walker demonstrated in a relatively large series that operative interference in cases of suspected fetal distress (according to criteria available at that time) did not improve the neonate’s condition and suggested that clinical criteria of intrapartum fetal distress wcrc probably inadequate. A critical rcporl OII intrapartum FHR auscultation ivith a ma.jor impact on American obstetrics was that ot Benson and associates”” 111 1968. Using the Collaborative Project’s data on nearly 25,000 deliveries, Benson and colleagues concluded that there is “no reliable auscultation indicator of fetal distress existing in term5 of FHR, save in all rxtreme degree.” Since FHR was often determined during the second stage and the typical “second-stage FHR brady car-dia” was not yet recognized as corn~no~~ and benign. this conclusion is now understandable. Using the same Collaborative Project
FHR data, Berendes”” reported in 1969 that in children who had low FHRs during labor four-year neurological examinations showed no critical difference in IQ scores from those with normal FHR. However, a small difference in certain neurological findings was noted, particularly in those children with low FHRs during the first stage of labor. The recent study of Haverkamp and associatesX6 in Denver, comparing clinical monitoring with electronic monitoring, suggests that the aban donment of the former may have been premature.
of fetal monitoring
Fetal phonocardiographic (PCG) recordings Fetal PCG recordings were apparently first made b) Hof%auer and Weis”’ in 1908 and later by Rockwood and Falls”H in 1923. Henley”” (193 l), employing tech.niques developed by the Hollywood industry for sound movies, recorded fetal heart sounds in many of his obstetric patients. Excellent fetal heart phonocardiograms can be obtained from the maternal abdominal wall with microphones with a low-frequency response (between 75 and 105 Hz). The successful PCG recording demands that there be a relative absence of excess abdominal wall noise or movement and is therefore of limited value as an intrapartum FHR monitoring system. Hammacher”” (1967) employed a logic system which converted fetal heart sounds to the square-wave form and counted three signals before accepting the sounds as representative of the FHR. Thus, a heart rate “accepted”
reliable. With this improved technique, Hammacher and Hewlett-Packard produced the first useful clinical fetal monitor. Even in the present time, the fetal PCG technique has much to offer, for it clearly distinguishes the fetal systolic from the diastolic intervals. These are, as noted below, of interest for determining fetal cardiovascular function. The PCG microphone also provides a noninvasive technique for measuring FHR beat-to-beat variability, unlike the Doppler transducer which often confuses the systolic with the diastolic pulses.
Abdominal fetal electrocardiogram Discussion of the development of methods for recording of the fetal electrocardiogram begin with Cremer’?’ 1906 human FHR recording. His subject is sometimes described as his pregnant wife and in other reports as a volunteer from Winckle’s antenatal ward. In 1906, some three years after Einthoven published his original description of the adult ECG, Cremer placed an abdominal electrode over the uterine fundus and inserted a vaginal electrode into a pregnant woman. The recordings showed distinct fetal electrocardio-
Fig. 3. Initial fetal electrocardiogram
recorded by Cremer in 1903. The fetal R waves are indicated by description in the baseline. (Reproduced with permission from Larks, S. D.: AM. J. OBSTET. GYNECOL. 77: 1109, 1959. published by The C. V. Mosby Co.)
gram complexes (Fig. 3). Over the next 2.5 years, there were only a few case histories”-“’ until Maekawa and Toyoshima”’ of Japan introduced-the use of the vacuum tube amplifier for fetal electrocardiogram detection and the number of papers on fetal electrocardiography increased progressively. Prior to availability of amplification, the use of a cervical or vaginal electrode was always described, but subsequent reports seldom mention its use. The intervening literature on abdominal fetal electrocardiography has been voluminous and somewhat inconsistent. The abdominal fetal electrocardiogram
the fetal position,42 twins, 45 congenital heart defects,“8 diagnosis of fetal life as early as 57 days after the last menstrual period,?” and in the evaluation of the general state of fetal health. The most enthusiastic supporter of abdominal fetal electrocardiography was LarksSo (1961) who reported a discernible ahdominal fetal electrocardiogram complex as early as 11 weeks after conception and suggested that the fetal electrocardiogram complex itself was useful for determining the state of fetal health. In 1942, Ward and Kennedy”’ reported a success rate in obtaining abdominal fetal electrocardiogram recordings varying from 70% at 20 weeks to 100% at term. However, others were seldom able to achieve
Fig. 4. Result of wide-band fetal electrocardiogram experiment (band width, 0.3 to 75 Hz; sampling rate 512 Hz). N: Reference input (chest lead); b; primary input (abdominal lead); c: noise canceler output. (Reproduced with permission from Widrow, B., Glover. J., McCool, J., et al.: I. E. E. E:. Trans. Biomed. Eng. 63:1692, 1975. published by the Institute of Electrical and Electronics Engineers.) such success.” In practical terms, often nothing more than slight interruptions of the maternal abdominal electrocardiogram (which supposedly occurred as the fetal heart rate) were taken as positive findings.“’ Under circumstances of such poor recordings, it is easily understood how a high incidence of false positive tests of FHR recordings occurred and how the impression developed that sometimes the heart of the dying fetus discharged at 300 to -100 bpm, termed tachyarrhYthmia.“‘. ” Some of these technical difficulties, such as i osing the fetal electrocardiogram at 28 to 3-1 weeks. lvere ascribed to vernix. others to the position of the placenta. In 1963, Kahn’,’ recorded fetal electrocardiograms from multiple sites over the maternal body and hypothcsi/.cd that fetal electrocardiogram currents were preferentially conducted through the umbilical cord and throygh the oronasal cayit), of the fetus.” Roche and Han’” (1965) and Oldenburg and Macklin” ( 1977) likewise concluded that the largest-magnitude f’etal electroc~artliogram signals are obtained with one electrode positioned over the anterioi- aspect of tlie fetal head. Determination of FHR. The abdominal fetal elec-
trocardiogram has been proved useful (~111~ as it technique for determining FHR. While enthusiasm for using this modality of recording the FHR has waxed and waned owr- the past 70 years. the techniques arc again a matter of great interest, for complications from internal direct scalp monitoring techniques are now more obvious.” To count thr FHR from abdominal leads requires a technique tix rcmo\-ing the maternal electrocardiogram compl~u from the tracing as well as excluding myometrial and maternal muscular activity. The maternal electl.oc.ardiogl-am complex is of grrater voltage and its R Icave of greater slope than that of the fetal electlocardiogra~n complex. Older techniques attempted to subtract the maternal electrocardiogram complcs from the recording. either by filtering or b) gating \vith special placement of thr abdominal arid chest wall electrodes. L~nfortunately, as man) as 509; of the f’etal heartbeats may coincide with Ihe maternal ones and ahout 20% of FHT are lost by these methods. The analogw cancellation technique IV;IS introduced b) Surcau and ‘t’rocellier”Y in 1961 and a multichannel method wab employed by Schuler”” in 196X. The simultaneous cancellation techniques had to be precise or else artifacts rhat could erroneously be counted as fetal R MXVCS UXSI‘V created in the recording. &lore recent techniques have sought to exclude the maternal elecwocardiogranl. based on difference in voltage and demand that Ihc maternal electrocardiogram be largei rhan the fetal electrocardiogram 1,) ;I specific ratio.” The use of’ coherent time averaging (