Clinical significance of fetal heart rate patterns during labor I. Baseline
From a population ~ti 2,774 high-r&k patierbts monitored durirlg labor, 1,304 single pregnunciu.v in cephalic presentation and with dirrct monitoring for at least I hour bejore completion or rP.sarean-sectio71 wre studied. The maternal and fetal clinical data and the tracings were hand reviewed, coded, and programmed.for computer anu[ysi.r. In the r-word ww .stndird baseline, itA changes (tachycardia, fixed, saltutory), the accelerations, rrrtd the de&rations (early, variable, late). Fzyty-f our p er cent had some type of FHR derrleration. .4rrrlrration.t were worded in over 12 per rent qf all cases and were aswriatcd with rord problems in 41 per rent. Subgrouping the patients by age of grstatiorl (536 wrks, 37 to 41 uwks(. and 242 uwks) revealed a IO per- rent prolonged gr>statiotl rat,) and only 0.8 pe?- renf prematwe: thew had a luuw 5 m&z zdr Apgar score. Fora. weight and uge were positive/y cow&ted with Apgar score. Bnseirrw rhwps wr( rrcwh more frrquerlt among pre- and postmature @ant>, purticularl? tcuhvrardia in th(J latter (40 &r cent). Thr premature ivfants had a 25 per cent incidence oj fetal distress and the postmtwr infants had 20 per cult. Neonatul morbidity and mortality rates were lrery high among premature infants und a mortality rate oj2.3 per cent was found among postmature injatlts. Saltatorv pattern and particularlvjixed baseline SBP~ rhararteristir oj polorlged gestatiori and placentul insuf~ cienry. With tachymrdia, they
WIDESPREAD application of intrapartum electronic, fetomaternal monitoring has been as much the result of intensive investigation in this field over the past 15 years as that of the very able promotional work of equipment manufacturers. Unfortunately, the possession of a monitor does not necessarily imply adequate training for its proper use. Furthermore, the recording of artifact-free tracings is only the prerequisite for the rational use of the information in making clinical judgments. There are not well-established
concepts in this area due, perhaps in part, to a lack of reports dealing with a sufficiently large number of patients. If one were to have such reports, it would then be possible to establish generalizations which could guide in the interpretation of the recordings obtained in specific clinical situations. Only with these tools we should be able to duplicate the improvement in neonatal mortality rates recently reported 2y* SO. ” with the use of intrapartum electronic monitoring. On the other hand, it has been shown that clinical auscultation alone cannot pick up all distresses. even those so gross as to terminate in death. 34 The currently accepted interpretations of changes in the fetal heart rate (FHR) patterns have been proposed by Han”. If an d Caldeyro-Barcia and his school”. ‘, w 25 and include: normal rate between 120 to 150 per minute6 or 120 to 160 per minute’“; brudvcardia when frequency is less than 120 per minute; tachycardia when over 160 per minute; “early” decelerations (type I dip): “variable” decelerations; “late” decelerations (type II dip): and absence of “beat-to-beat” variations of the
From thr Departmeni of Obstetric.s and Gyne~-rolvgy, C,~hirago Lying-in Ho.spital, C~Gwsity of Chicago. This work roas supported in part Spragw Memorial Foundation.
by a grant
The Annual Prim Aulard Paprr, presented Forty-third Annual Matting of the Central Obstetricians and 3.3)
Gen. 170 (13.0)
June 1, 1976 Am. J. Obstet. Cynecol.
Fig. 10. Continuous 80 minute recording accelerations seen on top became larger early decelerations blunted them. Shortlv around the neck was delivered.
of a 35 week induction for (bottom) and when completion thereafter a vigorous prematul-e
Baseline. The qualitative information obtained from the analysis of the tracings disclosed that more than 54 per cent had FHR decelerations of some type, and a variety of alterations of the baseline, the significance of which is, as yet, not very well understood. The detailed analysis of the dccr1rrmtion.c .ruh.group.~ will he made in subsequent papers; in the present work an evaluation of the various baseline chang-es which occur singly or in association or coincidence with FHR decelerations will be attempted. Rapid oscillations. The rapid oscillations of‘ the baseline were present whenever labors without serious complications were recorded. ‘They ranged around the average baseline between 5 and 10 beats per minute. even though on some occasions they may have had very regular, wider oscillations of up to over 15 peats peI minute (Figs. 2 and 3). The diminution of these oscillations, which under normal circumstances are maintained during accelerations or decelerations, frcquently represents alterations of fetal homeostasis and should he considered a warning sigtl. Accelerations. The transient increase of the FHR coinciding with contractions has bern recorded in 12.4 per cent of cases reviewed (Fig. 4). However, the erratic, unpredictable transient accelerations (Fig. 5)
PRM. ‘rhe small transient was imminent. increasing infant with a loop of cord
were recorded on rare occasions. ~L‘hese patterns have heen seen more often in the early part of first stage, showing a tendency to have superimposed (or be blunted hy) early or variable decelerations (Figs. 4 and IO). A very frequent coincidence was observed: in 41 per cent 01‘ cases they appeared in patients who subsequently revealed cord problems, particularly around the neck. Decelerations. Some mechanical factors may transiently affect the FHR. Among the most common, tlrclring ck,u~n (or pushing) efforts may have a profound influence upon the baseline pattern and even cause decelerations (Fig. 9, top) and rebound tachycardia. The effect more frequently seen is a short-lasting, rapid, early deceleration coincidental with the increased intra-abdominal pressure (Fig. 9, lower part). These decelerations are almost indistinguishable from early decelerations seen occasionally at the end of first stage (Fig. 10). On rare occasions the hearing-down efforts have no effect whatsoever upon the FHR. The bmehr ordinarily ranged between 120 and 150 per minute, but alterations were present in several pathologic clinical conditions with moderate to severe fetal distress. For this reason, it was decided to tabulate the patients according to age of gestation in an attempt
FHR patterns during labor. I 299
d 36 wk6 “EARLY”
Fig. 11. The patients grouped by age of gestation were compared for incidence of FHR decelerations, and cord problems. The groups are identified under the bars, and the exact percentages are shown on top of each. To the left are early decelerations, in the middle variable, and to the right late. On extreme right, cord problems. Statistical analysis was done for the entire
group, separately fo; cord problems.
to explore for possible correlations which may reveal possible unknown etiologic factors. The cases were thus grouped in those who were 36 and less weeks of gestation (considered chronologically premature), 37 to 41 weeks (considered term), and 42 weeks and over (considered postmature). Some quantitative data of the first and third groups are shown and compared in Table III. It is interesting to note that 10.1 per cent were postmature, whereas only 6.8 per cent were premature by dates, in contrast to average figures in our hospital of 13 per cent. This apparent discrepancy is the consequence of taking only age of gestation as standard for grouping (it is important to restate that all breech and twin births were excluded from the study group); when the cases were grouped by weight, those below 2,500 grams constituted 12 per cent of our total study, suggesting a high number of low-birth-weight infants. Almost all significantly different parameters were predictable because they are age dependent, with the exception of average Apgar score at 5 minutes, and fetal/placental ratio which was lower among prematures and may have pathophysiologic implications. Significant positive correlations were found in the premature group between gestational age and Apgar scores at 1 and 5 minutes, as well as fetal weight and Apgar score. Furthermore there was a positive correlation between gestational age and F/P ratio, but a negative one between Apgar scores and number of decelerations. The tabulation of some qualitative variables and their comparison among the three groups reveals some unexpected coincidences. In Fig. 11 are shown, for each separate group, the proportion of cases present-
ing the three types of decelerations used for classification, and the same for cord problems. The incidence of variable decelerations and cord problems affects almost one half of all prematures, the other groups having a much balanced proportion of this and the other decelerations. Tachycardia. The presence of early tachycardia (present from the moment the recording started) was very high among the premature infants, and also found in a disproportionate number of postmature infants (Fig. 12). The development of tachycardia following alterations of the FHR patterns is also shown in the same figure, the term infants being significantly less affected than both the pre- and postmature infants. Saltatory and fixed baseiine. The study of two other baseline changes, saltatory and fixed, is very revealing because it shows impressive differences, seemingly dependent on gestational age (Fig. 13). Almost 40 per cent of prolonged pregnancies had a fixed baseline of FHR at one time or another, while only 6 per cent of term
strikingly significant manner, the postdated infants had a saltatory pattern. These various changes (saltatory, fixed, and tachycardic baseline) occurred in a transient manner, again much more often among the postmature infants, and the pre- and postmature infants had them in a sustained manner in very high number.
shifting back and forth from one to another, suggesting that perhaps they may have a common underlying predisposing Fig.
June 1, 1976 Am. J. Obstet. Gynecol.
12. Incidence of tachycardia (over 150 beats per minute) observed in the three groups. On the left those who already had tachycardia at the start of the monitoring, and on the right those in whom it subsequently developed; note how high for prematures and postmatures.
The diagnosis otfrtul &YP~J was made in more than one quarter of the premature infants and almost 20 per cent of postmature infants-a significant difference compared to the term group. The same relatively high number of premature infants were born depressed (Fig. 13). The ultimate test: the neonatal morbidity and mortality rates were significantly higher among the premature infants. as might be expected (Fig. 16). It is worth noting that no postmature infant had RDS, but a high number of them died in either late first stage or the neonatal period, in a much higher proportion than the term ones. This outcome and the FHR alterations observed very often among the postmature may indicate that these fetuses have signs of intrapartum distress which should be appropriately interpreted. The above-described fixed baseline seems very characteristically present in the postmature labor. It may have associated other changes as accelerations and any of the three types of decelerations. When it is recorded with late decelerations and/or tachycardia it becomes a very ominous sign, and prompt action should then be taken (Fig. 14) because the deterioration of these fetuses may be extremely rapid. Isolated tachycardia. This should be considered as a warning sign because it may be due to a number of etiologic factors. When no cause may he found it is labeled “idiopathic*’ and is then of benign significance. More often it occurs following episodes of severe variable or late decelerations (Figs. 6 and 7), when it is called r&ourld or mnpnsatorv tachycardia and should be interpreted as sign of fetal distress. Still in other circumstances it may be among the first indications of
Table III. Average clinical data of cases under weeks’ and over 41 weeks’ gestation*
Patient’s age Gestational age Dm-ation recording (min.) No. contractions No. decelerations Apgar at I minute Apgar at 5 minutes Fetal weight (Gm.) Placental weight (Cm.) Fetal/ pktcental ratio
17.7 7.7 9.9 3.468.0 45-1.0
*Statistical analysis calculated by the two-sample
maternal hyperthermia which could be caused by different etiologic factors. The most common cause of intrapartum hyperthermia is amnionitis, but dehydration, fatigue, excess heat, etc. may be important c,ontributing causes of poor temperature regulations. The fetal heart rate will respond rapidly when therapeutic measures are implemented and effective to lower the temperature. Direct stimulation of the fetal head during pelvic examination will almost predictably cause an impressive deceler-ation of the FHR, particularly when pressure is exerted over the fontanels (Fig. 9).
Comment The mate& included in this analysis represents only 47 per cent of all monitored patients during the 4% years of the study. Excluded were only those with multiple pregnancies, breech or transverse lie, 01 the internal recording was less than 60 minutes’ duration. Thus the selection of this obstetric population was made only on the basis of the recordings obtained and the presentations of the fetus. Because it is a relatively Lange number. it represents quite well the clinical findings expected in a high-risk population (excluding malpresentations and multiple gestations). Only 42.4 per cent delivered spontaneously whereas 1 1.:) per’ cent had cesarean sections, contrasted with 53 and 8.08 pet’ cent. respectively, for the over-all hospital popula-
FHR patterns during labor. I 301
Fig. 13. The incidences of saltatory on the left. The number of fixed in classifies those into alterations which remainder of the recording. Note alterations.
and fixed baseline occurring in the three groups are compared prolonged gestation is impressive. The right side of the figure were transient and those which were sustained throughout the how many pre- and postmature infants had these baseline
3415 pm FETUS
Fig. 14. Continuous 100 minute recording of enhanced labor in 42 week pregnancy. On top, under continuous O2 administration are seen short bursts of saltatory pattern coinciding with the peak of contractions. To the right, suddenly, the baseline became fixed. At the bottom, a burst of marked saltatory pattern appeared followed by decelerations, and wavy fixed baseline. By cesarean section a vigorous infant was obtained.
rate there are no repeats; these are included per cent of the total obstetric population. More
of all patients
of deceleration, reported
highest all these
a sizeable incidence series, very
number was that
of cases.lOz of variable
by others 35 Of
who the in the
June Am. J.
d 36 wks (88 cases),
3 42 wks (132 cases1