Clinical significance of fetal heart rate patterns during labor

Clinical significance of fetal heart rate patterns during labor I. Baseline

patterns

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

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

from

thr,

The Annual Prim Aulard Paprr, presented Forty-third Annual Matting of the Central Obstetricians and
at thr A.ssociation Sprlng.y.

Krprint Hyrrson 60637.

CampurL Chicago,

rrqu&.\: Profewr,

Dr.

Luis A. Cibih, 584 I MaTland

Ma9 .4w.,

of

Illino~r

290

Volume Number

FHR patterns during labor. I 291

125 3

4k 112-22-07

2200

gm FETUS

Apgor

9-10

Placenta

400

gm

Z-15-72

Fig. 1. A 16 minute recording of intrauterine pressure, lower channel, and FHR, upper channel. The scales are shown in the ordinates; the time in the abscissa is 1 minute between the heavy vertical lines. This tracing illustrates the only case recorded with a steady baseline of 110 to 115 beats per minute. Moreover, it shows four early decelerations. The infant was “small for dates” and did well neonatally.

FHR baseline. A number of other investigators have contributed with human observations and animal experiments which support the suggested pathophysiologic interpretations of these classifications.‘, 3, 16* 27, 31

With the establishment of the Section of Maternal and Fetal Medicine at the Chicago Lying-in Hospital in June, 1970. it was decided that all high-risk pregnant patients in labor, as well as all uterine stimulations with oxytocics, should have continuous uterine contractions (UC) and fetal heart rate (FHR) monitorings. For this purpose there were used either “external methods” (tocotransducer and ultrasound transducer), or “internal,” “direct” methods (intrauterine catheters and subcutaneous electrodes). From June, 1970, to December, 19’74, a total of 12,339 patients were delivered at the Chicago Lying-in Hospital and 2,774 of them were continuously monitored from 30 minutes up to 30 hours. It was decided to analyze this material, carefully reviewing the tracings (uterine pressure and FHR), to attempt to correlate their changes with clinical conditions of the mother and fetal outcome. This was done with the intention of reporting a moderately large clinical experience gathered in a teaching institution and, thus, not representative of what could be expected in a model maternity hospital. Moreover, the clinical material is heavily loaded with maternal pathologic conditions because these were the reasons for instituting supervision by continuous monitoring.

Materials and methods From the total pool of monitored patients, there were selected for analysis only those who had “direct”

recordings for at least 60 minutes before dilatation completed, or in whom the record was discontinued so that a cesarean section could be done (only two very good “external” recordings were included). Thus there were reviewed 1,304 consecutive cases of single pregnancies in cephalic presentations (the only excluded cases were 112 patients who had significant FHR changes following the administration of a paracervical block). The records were hand reviewed, coded, and programmed for computer analysis of the various possible correlations between fetomaternal clinical conditions and patterns of FHR tracings. Clinical data. From the maternal chart were extracted: patient age, gestational age, pathologic condition-(l) normal, (2) hypertension. or (3) premature rupture of membranes; (d) “others” (which included diabetes, abruptio placentae, premature or postmature labor, cardiopathy, hyperthermia, desultory labor, and miscellaneous). (When there was more than one condition in a patient, the clinically more important was coded.) The type of labor (spontaneous, enhanced, induced) was noted. There were also noted the presence of clinical fetal distress (meconiumstained amniotic fluid, sustained fetal tachycardia, markedly irregular heart rates), the medications administered (analgesia, magnesium sulfate), the type of anesthesia for labor/delivery (local, conduction, general), and the type of delivery (spontaneous, forcepsvacuum, cesarean-section). From thefetal chart were extracted the Apgar scores at 1 and 5 minutes; condition of the cord-free, or problems (which were coded together: around neck, limbs or shoulder, velamentous insertion, true knots, too short or too long, against head, etc.: when there

292

Cibils

June 1, 1976 Am. J. Obstet. Gynecol.

3495

+ 96-53-00

LARGE *

“RAPID

gm

FETUS

OSCILLATIONS”

F.H.R.

INTRAVENOUS gm FETUS Apt&w

2955

80-18-59

of

Apf)or

Placsntol

B-IO

BASELlN,E

750

UNAFFECTED

OEMEROL 9-10 Placenta

675

pm

qm

6-24-71

BY 2-4-74

i Fig. 2. The top tracing is a 40 minute recording of a term spontaneous labor illustrating the average type of normal rapid oscillations of FHR; they occur 4 to 5 per minute and oscillate 4 to 10 beats per minute. Small early decelerations coincide with most contractions. The bottom tracing is a 50 minute recording of a term induced labor and illustrates rapid oscillations of very large range, 12 to 20 beats per minute. It furthermore illustrates that intravenous administration of 50 mg. of meperidine to the mother did not affect those rapid oscillations.

that there were and the placental weight: the neonatal evolution until discharge, with specific attention to respirator-y distress syndrome (RDS) and death (the autopsy reports were reviewed when available). Data from the recordings. The duration of the period analyzed (in minutes) was noted along with the was no specific

no “cord

number

notation

problems”):

ofcontractions

it was assumed

the birth

of more

weight

than

IO mm.

Hg

intensity

recorded during that time. In the tracings the following were analyzed and noted. 1. The busclinr FHR between 120 and 150 beats peg’ minute is considered normal: over 1.50 per minute is considered tachycardia at the beginning of the recording. This was calculated by taking the rate between contractions and for a period of over 15 minutes. When there were decelerations, the baseline was calculated after complete recovery. Only one case had a

steady rate of less than 120 per minute, thus considered bradycardia (Fig. 1). 2. The “rapirl oscillations” of the baseline5* 6 are small fluctuations occurring at a frequency of 3 to 6 per minute, with a range of up to 15 beats per minute (Figs. 2 and 3). They seem to be present in all normal tracings and are also called “beat-to-beat variations.“‘3, I5 3. “Accelrrutions” are transient increases of the rate, of more than 10 beats per minute, lasting usually less than 1 minute, and returning to control levels. These accelerations may coincide with the uterine contractions. and seem to be triggered by them (Fig. 4), or they may occur in a completely unpredictable erratic pattern

(Fig.

:i).

4. Durrlrratioxs are transient decreases of the rate lasting at least 20 seconds. The shape of the tracing and its time relationship with uterine contractions have been the basis for their classificatiox?, ‘* “3 ‘a. I5 into (1)

Volume Number

FHR patterns during labor. I 293

125 3

“RAPID

OSCILLATIONS” 2875

# 116-35-13 ,-*“i.

of the

gm FETUS

--.--..,-.,

-.j

FETAL

Apgor 6-9

.-

^^.r^^‘.i

2750 gm FETUS

RATE

BASELINE

625. gm

Placenta

^_^_.^_^-^-^^__^^

Fig. 3. A 20 minute recording of an induced labor in a term same as in Fig. 2 but the paper speed is double, to illustrate oscillations occur 4 to 5 per minute and oscillate 8 to 15 beats with contraction occurs in the third before last contraction

+ 109-36-39

HEART

I-17-73

^

pre-eclamptic labor. The a possible misinterpretation. per minute. One transient shown.

Apgar 8-10 I

scales are the The rapid acceleration

Placenta 575 gm Q-21-71 ec : : : r crc K c c : c c C.,E “,” : Gc : c : / ~~-, --, -I

’

:

I

r ? 9; ./ i i

“ACCELERATION”

of

c109-25-41 ..‘...I-

3600 .

.

. . .

FETAL gm

with

HEART A. Jar

FETUS

. J,.....~.““~..~..;..-.

.

. ..^.

-.

8-10

UTERINE Placenia _ .

CONTRACTIONS 600

gm .

^‘,

_

S-11-72 ._

I

Fig. 4. The top shows a 40 minute recording of a term enhanced labor where transient accelerations with contractions occur in the left half. In the right half the accelerations are blunted by typical early decelerations. The bottom tracing illustrates 50 minutes of recording in a term enhanced labor where large transient accelerations of FHR started close to the peak of most contractions. There were no obvious cord problems in either one of these cases.

294

June I. 1976 Am. J. Obstet. Gynecol.

Cibils

+ IIS-33-

2600

85

Aoaar

am FETUS

Fig. 5. A 40 minute recording of an induced illustrates the repetitive occurrence. on a normal unrelated to contractions. Uneventful outcome.

#

3200

65-28-03 .I

2N

gm

FETUS

_I.,

MO

Placenta

425

labor in a 37 week baseline, of significanr

Apgar

8-10

am

pre-eclamptic pregnancy. It transient accelerations totally

Placenta

700

gm

Ll ,a”

LA_)12

2 -21-74

./

9-27-72 Al:,,

7

ii0

.-.

..“A”

I

I

Fig. 6. A continuous 40 minute recording of a labor induced at term for PRM. The top illustrates a normal FHR baseline and the occurrence of variable decelerations, deteriorating and followed by increasing baseline. The bottom starts with two prolonged decelerations followed by saltatory pattern on a generally bradycardic haseline (average around 100 per minute.). Delivery 30 minutes later produced a normal infant with two loops of cord around the neck.

early I32 I5 or type II dips. For the

or (3) lutr or type 6 (2) uariablu, of the present work. an “K&?

I dips,j. purpose

&c&ration” was considered least 10 beats per minute coinciding

with

evidence

of maternal

in the

intrauterine

Caldeyro-Barcia contraction deceleration

a decrease (regardless

a uterine

contraction,

but

maneuver

(Figs.

Valsalva tracing. and

reaches coincides

As dclined

associates’, its

of the FHR of at of the baseline) without 1 and

by Hont2,

’ it starts

before

2)

“zwriable

dwrluation,”

beats

per

minute:

seconds,

the

tracing

having

t3 and

outstanding

the

deceleration

peak and the “valley” of the in time very closely kvith it. A

as described

usually in the early the heart rate falling

intensity unpredictable

part of the very rapidly this

recovery

by

is sustained being

Han”,

for

equally

between rapid,

a

U-shaped pattern characteristic is that neither nor

of

its duration

uterine or

are In

the

over-all

(Fig. 6). ‘The the degree of therefore

cases

90

10 to 50

in proportion

contractions,

variable.

r3 starts

rise of the contraction, to between 60 and

of

repeated

to the being and

Volume 125 Number 3

FHRpatternsduringlabor.I 295

“LATE”

DECELERATIONS,

# 108-11-74

3325

on Continuour

gm

“SALTATORY”

FETUS

Apgar

4-4

BASELINE Placenta

and TACHYCARDIA 600

gm

8-21-73

00 /

Fig. 7. Induction of labor at term. The top 50 minutes of monitoring illustrate a series of late decelerations with the baseline rising between them. In addition there is a clear saltatory pattern on the ascending limb of the deceleration and on the baseline. Under the effect of O2 the amplitude of decelerations dropped and the saltatory disappeared. The bottom tracing, 2 hours later, shows recurrence and worsening of decelerations, rising baseline, and diminution of rapid oscillations. A cesarean section revealed a concealed abruptio placentae and produced a depressed infant.

prolonged variable decelerations there is a transition pattern evolving toward the next described. In the “lute decelerations” described by HorP l4 or type II dips by Caldeyro-Barcia and associates,5* 6 the beginning of the fall in rate starts when the contraction reaches its apex or slightly later; its lowermost point is usually more than 20 seconds after the contraction began its relaxation. The recovery is marked by slow rise, the total duration of the deceleration being close to 60 seconds (Fig. 7). Usually the amplitude of the FHR drop is directly proportional to the intensity of uterine contractions, and with frequent contractions they tend to be progressively more severe; conversely, they become less severe when the frequency and/or intensity of the contractions diminish. 5. A “jixed baseline” is recorded when the normal “rapid oscillations” are not present, or their range is so small that it fluctuates within less than 3 beats. The tracing has an extremely clean and regular appearance (Fig. 8). It may be present from the start of the record or appear in the course of labor. It may also develop after decelerations have occurred, in which cases its appearance is not as flat as shown in this illustration.

The described acceleration and deceleration may still be recorded with this type of baseline (Fig. 14). It is equivalent to the pattern described by Hon13r l4 as “absence of beat-to-beat variation” and by Hammacher and associates” as “silent.” 6. The “saltatory” pattern was observed and defined when the range of the rapid oscillations recorded was of 20 beats per minute or more, and oscillating between two and four times per minute (Figs. 6 and 7). These rapid changes make them clearly different from the previously defined patterns. This pattern may occur during uterine contractions only, between contractions, or alternate with decelerations. On the other hand, their appearance may be transient during the course of labor or become permanently established until delivery. They probably correspond to what Hon defined as “marked irregularity.“12-15 7. It was considered that “tachycardia” was present when the baseline heart rate was over 150 per minute. When decelerations were present, only the period after recovery was taken: on occasions, this was only a brief period but sufficient to indicate the basal rate (Fig. 7). 8. “Bradycardia” was considered to be present when

296

Cibils

June 1, lY7ti .4m. J. Ohstet. Gynecol.

“FIXED“

F.HR.

BASELINE

-

DELIVERY

55 minutes

Fig. 8. Sixteen

minutes of enhanced labor in a 36 week pre-eclamptir gestation. Fixed beats per minute unaffected bv contractions. Delivery produced a mildly depressed, infant, who did well.

Table I. Average clinical studied (total 1.304)

data from all patients

LATER

low-birth-weight

tions, like pelvic examinations, 9).

baseline

at 135

were disregarded

(Fig.

Results Patient’s age Gestational

age (wk.)

Duration recordings

?3.6 39. I 238

13-46 27-44

60-999

6.9 2.3 172.5

81.6 16.8 7.x 9.3

I‘)-5‘34 b .. o- 195 o-9 O-IO 850-4950 230-999

60.5 25.5 1 .i 1.2 582.8 136.5

(min.)

No. contractions No. decelerations Apgar at 1 minute

Apgar at 5 minutes Fetal weight (Cm.) Placental weight Gm.1 Fetal/placental ratio

3,141.5 613.5 5.22

2.4&8.5

0.87

the rate was consistently below 120 per minute. This may represent a steady baseline or be the consequence of repetitive severe decelerations which do not recover completely before the next one starts. The latter pattern has been called “overlapping type II dips” by Caldeyro-Barcia and associates.“~ ’ The described changes may have occurred only transiently or be permanently established: these two circumstances were separately coded. Likewise, when there was clear evolution from one pattern to another (i.e., late decelerations followed by tachycardic baseline) it was so noted. Finally, the total number of decelerations was noted for each case, coding on the more severe one when there was association of them. All the observations here reported include only the period befow ccrui~al dilatation completed because maternal bearing-down efforts often trigger FHR changes. The transient changes produced by external manipula-

In Table I may be seen the averages of some quantitative clinical data of the patients studied. The very large ranges suggest an inhomogeneous population of patients which should be subgrouped in order to find the significance of some of these variables. The qualitative data extracted from the charts and from the analysis of the recordings are shown in Table II. It may be seen that there is a very high incidence of patients undergoing their first labor- which. in part, is a reflection of the parity of our obstetric population. Only 20 per cent of them were considered to have a normal prenatal course until the moment monitoring began, whereas the remaining 80 per cent were affected by one or more pathologic condition. Almost ‘75 per cent of the patients in this group necessitated either enhancement or induction of labor, whereas almost 14 per cent had clinical signs or symptoms of fetal distress with almost the bame incidence of neonates depressed at the first minute of life. Slightly more than 25 per cent had cord problems, the presence and signs of which may have prompted the obstetrician to institute cominuous monitoring. About 42 per cent were delivered spontaneously, whereas over 1 1 per cent had cesarean sections. all nonelective. The neonatal mortality rate of 1.3 per cent includes infants who had respiratory distress syndrome (RDS) as well as those with congenital malformations incompatible with life. The morbidity late of 1.2 per cent RDS represents only those who survived.

Volume

125

Number

3

FHR patterns during labor. I 297

#

3795

124-66-60

EFFECT

of

gm FETUS

BEARING

DOWN

3255

1c 63-73-36

Apgor

om

7-9

EFFORTS

FETUS

Placenta

upon

Apaar

F.H.R.

7-10

800 pm

4-11-74

DELIVERED

I9 min. LATEF

Placenta

750

gm

12-31-72

Fig. 9. Effect

of bearing-down efforts upon FHR. The top 50 minute tracing, from a term induced pre-eclamptic labor, illustrates the rapid drop of FHR and slow recovery following pelvic examination. Subsequent contractions with mild pushing efforts triggered a saltatory-like pattern, but when the pushing was vigorous (right part) the FHR fluctuations were very dramatic, occurring with each one of them. The lower 50 minute tracing, from a term spontaneous labor in second stage, illustrates transient accelerations of FHR with contractions and superposition of large early decelerations every time the patient pushed. Both of these patients delivered term-size vigorous infants.

Table

II. Distribution

of some

pertinent

Mult

Number Percent

731 (56.1)

Normal

573 (43.9)

263 (20.2)

Pre-existing tachycardia

Number Percent

1,304

cases

studied

Type

of labor

deceterations

FHR

Hypert.

PRM

Other

spent.

Enhan.

Induc.

No

Early

Var.

219 (16.8)

463 (35.5)

359 (27.5)

338 (25.9)

521 (40.0)

445 (34.1)

598 (45.9)

247 (18.9)

312 (23.9)

baseline Tachyc

changes

Yes

No

Salt.

Fixed

No

1,217 (!>3.3)

87 (6.7)

1,046 (80.2)

102 (7.8)

156 (12.0)

1,112 (85.3)

Cord

problems

975 (74.8)

the

condition

No

No

Number Percent

FHR

among

Maternal

Parity

Null

data

ardia

Yes

192 (14.7)

Clinical distress

f. NO

1,123 (86.1)

Apgar

5 min.

Spent.

Fort. VllC.

c/m.

181 (13.9)

183 (14.4)

41 (3.1)

553 (42.4)

604 (46.3)

147 (11.3)

Anesthesia

for delivery

Analg.

MgSO,

329 (25.2)

847 (65.0)

413 (31.7)

(EO)

No

(;.iO)

of delivery

I min.

medication No

Type

147 (11.3)

Yes

Intrapartum

Yes

5 6

Late

Local

Conduct.

(619:)

264 (20.2)

Neonatal

Gen. 170 (13.0)

condition

Death

RDS

Good

(i.730)

$0)

1272 (97.5)

298

June 1, 1976 Am. J. Obstet. Cynecol.

Cibils

#

101-92-7s

2045

gm

FETUS

Fig. 10. Continuous 80 minute recording accelerations seen on top became larger early decelerations blunted them. Shortlv around the neck was delivered.

Apgar

7-10

PLACENTA

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)

500

gm

7-4-73

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

Volume Number

FHR patterns during labor. I 299

125 3

d 36 wk6 “EARLY”

(88

cases),

37-41

wks

(1084

“VARIABLE”

cases),

342

“LATE”

wks (132

CORD

cases)

PROBLEMS

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

deceleration

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

infants

had

it.

To

a lesser

degree,

but

still

in

a

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.

These

together

because,

changes

were

grouped

very

often,

one

and may

see

compared patterns

shifting back and forth from one to another, suggesting that perhaps they may have a common underlying predisposing Fig.

14.

cause.

A typical

example

is illustrated

in

300

d36

Cibils

wks(88

June 1, 1976 Am. J. Obstet. Gynecol.

cases).

37-41

wks (1064

cases),

242

PRE-EXISTING

SUBSEOUENT

TACHYCAROIA

TACHYCARDIA

wks

(132

Cases)

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.

Fig.

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

~57

X8.(1

17.7 7.7 9.9 3.468.0 45-1.0

669.0

4.56

*Statistical analysis calculated by the two-sample

t test.

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-

Volume Number

FHR patterns during labor. I 301

125 3

“SALTATOAY”, “FIXED”

-SALTATORY”

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.

d

8

TRANSIENT

TACHYCARDIA SUSTAINED

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

120-53-96

“FIXED”

Apgar

9-10

725

Placenta

6-8-73

gm

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.

tion pointed

during out

the that

same

4%

year

in the

11.3

per

span. cent

It

rate there are no repeats; these are included per cent of the total obstetric population. More

than

50 per

cent

of all patients

should

be

in the

of deceleration, reported

cesarean-section 8.08

highest all these

had

some

type

The

comparable

a sizeable incidence series, very

high

to findings

number was that

and

the

incidence

of cases.lOz of variable

lowest

the

by others 35 Of

these,

decelerations late

decelerations.

of primiparity

reffects

who the in the

302

Cibils

June Am. J.

d 36 wks (88 cases),

37-41

wks

(1084

cases),

3 42 wks (132 cases1

$36

wks (88

cases),

37-41

RESPIRATORY

% p=<

0

023

---

wks

(1084

DISTRESS

cares), PERINATAL

1, 1976

Obstet. Gynecol.

2 42 wks (132

cases)

MORTALITY

17 Chl sq. (4 d.f.) = 62.9

20

p=<

0.0005

IO

0 s 36

37- 41

242

s 36

37-41

242

Fig. 15. Incidence and comparison of clinical fetal distress and Apgar scores of 6 or less among the three groups studied. Preand postmatures had high distress rate. Prematures had high depression rate at 1 minute.

Fig. 16. Incidence and comparison of neonatal morbidity (RDS) and uncorrected perinatal mortality rate among the three groups. Premature infants are high on both subgroups. Postmature infants had no RD.6 but high mortality rate.

trend in our patient population, perhaps further distorted by the number of pre-eclamptic patients admitted in our hospital. Likewise, the incidence of 25 per cent cord problems is somewhat higher than expected from an average population lo but found in other high-risk groups.28 perhaps because the very presence of the cord complication and its effect on fetal heart tones alerted the obstetricians to monitor some patients. Further evidence that this group was made of “problem patients” is the fact that only 25 per cent evolved as spontaneous labor, and that only 20 per cent were considered normal before monitoring (these include all elective inductions. slow progressing labors, etc.). These considerations are intended to re-emphasize that this population is not representative of an average obstetric population but rather of a selected high-risk group which predictably will have a high incidence of intrapartum distress and fetal depression

significance has not been well understood. They seem to represent a balance between vagal and sympathetic influences (or tone) upon the fetal heart,3* 4, I43 Ifi, 24, “3 33 influences which may be drastically altered by changes in oxygen tension, blood pH, or both. It is not clear whether there is a physiologic change of these oscillations in response to chronologic maturation of the fetus. Some cardiovascular reflexes are known to appear in sequential manner in animals2s y The significance of transient acc&rations has not been discussed in any detail by those who have studied FHR patterns,s. 6. 13. 15, r8 They have generally been described as constituting a good signlYa 28 or dismissed as without significance. Only recently’g it was stated that they may foretell the presence of cord problems: this has been confirmed in the present study because a coincidence of both in 41 per cent of patients is extremely high. It is difficult to speculate about the mechanism involved because the hemodynamic alterations produced by compression may trigger opposing reflex responses. The baseline changes triggered by increased maternal intra-abdominal pressure and Valsalva maneuver have been observed by others.3* r” They seem not to affect the condition of the infant at birth,3 although they have a very disquieting appearance on the tracings. Sustained tachycardia has been associated by s,,me author53. 4. 7, 17. 18, 20, 25 with fetal distress, whereas others could not find a correlation between them.28~ 3r It has been shown to occur as rebound response following transient episodes of hypoxic bradycardia,1.6, ’ a fact repeatedly observed and well documented in the present series. The very high proportion of tachycardic fetuses among the premature may repre-

at

birth.22,

The among

28. 33

extremely high incidence of cord problems the premature is a perplexing observation about which one may only speculate. It could be, in part, due to the fact that small infants surrounded by a disproportionate amount of amniotic fluid have more room between fetus and uterine wall and thus can more readily compress the cord. This may drop easily between head and shoulders and lower segment because there is enough space in between to accommodate the cord. Be that as it may. half of the premature-by-dates infants have cord problems and the obstetrician should be aware of this. The rapid m.tri/lr&on.s of the baseline have long been described to occur in pregnancy and laboti6 but their actual

Volume 125 Number 3

sent the frequently mentioned “physiologic” high heart rate at this stage of gestation, but it certainly should no longer play a role in postmature infants. The finding that so many more premature and postmature infants developed tachycardia must be considered to represent a sign of disturbed fetal homeostasis when evaluated in the context of the other alterations of the baseline. Other authors have reported that infants born follouing episodes of sustained tachycardia were depressed at birth,4* ‘2 ‘* 18. *‘* 25 but only Wood3? was unable to corroborate this observation. Ajixed boseline has been described to occur in a high number of infants born depressed’, llr 35 and to be present in cases of placental insufficiency.4z 7* rl* 23 Those findings have been corroborated by the present study (Figs. 5 and 13). Furthermore, in the present series it was observed at some time during labor, often sustained, in almost 40 per cent of all gestations of 42 weeks or more but in only a minimal proportion of term fetuses and 13 per cent of premature infants. This finding would suggest that a fixed baseline is almost characteristic of prolonged gestation. The interesting phenomenon is that when it is a transient episode it usually follows periods of late deceleration or fetal distress, thus being a possible manifestation of fetal distress. It has also been described to occur in cases of placental insufficiency,‘, l1 a fact repeatedly documented in this series (Fig. 8). These three different circumstances when a fixed baseline may be predictably recorded are situations of relative or compensated fetal distress. It is only after some time with a fixed baseline that the FHR altered by acute distress will resume the normal rapid osciliations.7 Snltutoyy bareline has been associated by Hammacher and associates” with cord complication and considered “a sign of increased fetal distress.” Han’*, r3* I5 has probably described it by the name of marked irregularity but without ascribing to it any specific pathologic significance. The present series of cases suggest that it occurs in a high number of fetuses in distress. particularly in those beyond term (Fig. 13). An indication of its pathophysiologic significance could be inferred from its extremely frequent association with tachycardia and its pendular alternation with fixed baseline (Fig. 14). As with the latter, it frequently may be observed to occur transiently following periods of brief hypoxia (Figs. 6 and 7) or to disguise a deceleration (Fig. 14). It seems then to be another subtle sign of fetal distress, present particularly in mature and postmature fetuses. The frequent association with cord complications” could not be substantiated in this work. The recording of unexpected tachycurdia should

FHR patterns during lath.

I 303

always be considered a potentially ominous sign. Rarely will it be idiopathic and without apparent pathologic significance, particularly when maintaining good rapid oscillations of the baseline. More often they will be a fetal response to some type of stressful situation, the most common one being hyperthermia. It has been a long-standing clinical practice to give oxygen to the mother under these circumstances, in addition to attempting a specific treatment. When this is successful one may be able to observe the complete, slow regressions to normal patterns. This support to the infant, given empirically, seems to be extremely important because in subhuman primates it has been shown recentlyz6 that maternal hyperthermia leads rapidly to fetal acidosis and hypotension, even when good oxygenation is maintained. The high proportion of clinical fetal distress among pre- and postmature infants suggests that this association of high-risk gestation leads to serious jeopardy for the fetus, as may be seen from the high incidence of depressed infants at 1 and 5 minutes of Iife. Others have studied this problem from a different angle and reached equivalent conclusions.21a ** The most revealing observation was not the very high number of premature infants who died or had RDS, but that postmature infants died in much higher proportion than those at term. This occurred in late labor or neonatal life after indications of FHR alterations compatible with distress, but without what one would label as obvious signs of impending death. After the detailed analysis of those cases it seems necessary to reappraise the significance of FHR changes and relate them more specifically to chronological age.8 Only then one could make an adequate interpretation of the clinical conditions of the infant and take the most convenient therapeutic step. Among the changes, saltatory, fixed, and tachycardic baseline were prominently present whereas the classic pattern of deceleration was almost absent. From the foregoing, one may conclude that in a selected population of high-risk obstetric patients who had single pregnancies in cephalic presentation the following have been observed. 1. Only 20 per cent were classified as normal before monitoring and 25 per cent had spontaneous labor. 2. Spontaneous delivery occurred in 42.4 per cent and 11.3 per cent had primary cesarean sections. 3. Slightly more than 25 per cent had cord complications (especially around neck); 19, 24, and 11 per cent had early, variable, and late decelerations, respectively. 4. Clinical fetal distress was present in 14 per cent and slightly more were depressed at birth.

304

Cibils

5. The uncorrected neonatal morbidity and mortality rate was 2.5 per cent. 6. The grouping by gestational age of this population revealed that 46 per cent of premature infants had cord problems with variable decelerations. 7. A large proportion of premature and postmaturr infants have pre-existing tachycardia, or may be expected to develop it during labor. 8. A fixed baseline seems almost characteristic of the postterm infant, and the saltatory pattern to a lesser extent. The same occurs with placental insufficiencv. 9. Baseline alterations (saltatory, fixed, and tachycardia) occur much more often among pre- and postmature infants than at term. 10. Prematurity and postmaturity predispose to intrapartum fetal distress.

REFERENCES

I. Althabe,

2. 3.

4.

.5

6.

7.

8

9

10.

I I.

12.

O., Schwartz, R. L., Pose, S. V., Escarcena, L., and Caldeyro-Bar&, R.: Effect on fetal heart rate and fetal PO, of oxygen administration to the mother, AM. J. OBSTET. GYNECOL. 98: 858, 1967. Barcroft, J.: Researches on prenatal life, Oxford, 1946, Blackwell Scientific Publications, Chap. XII, pp. 123-144. Brady, J. P., James, L. S., and Baker, M. A.: Heart rate changes in the fetus and newborn during labor, delivery and immediate neonatal period, AM. .J. OBSTET. GYNECOL. 84: 1, 1962. Brady, J., James, L. S., and Baker, M. A.: Fetal electrocardiographic studies, AM. .J. OBSTET. GYNECOL. 86: 785, 1963. Caldeyro-Barcia. R., Mendez-Bauer-, C., Poseiro, J. J.. Escarcena, L. A., Pose, S. V., Bieniarz, J., Arm, I., Gulin, L.. and Althabe, 0.: In Cassels, D. E., editor: The Heart and Circulation of the Newborn and Infant, New York, 1966, Grune & Stratton,Inc., pp. 7-36. Caldeyro-Barcia, R., Mendez-Bauer, C., Poseiro, J. J., and Pose, S.: Fetal monitoring in labor, in Wallace, H. M., Gold, E. M. and Lis, E. F., Editors.: Maternal and Child Health Practices, Springfield, Ill.. 1973. Charles (1 Thomas, Publisher, pp. 332-394. Cibils, I.. A.: Clinical significance of fetal heart rate patterns during labor. II. Late decelerations, AM. J. OBSTET. GYNECOL. 123: 473, 1975. Cibils. L. A.: Clinical significance of fetal heart rate patterns during labor. III. Agonal pattern (in preparation). Dawes, G. S.: Cardiovascular adjustment of the fetus during asphyxia: the aortic chemoreceptors, in Perinatal Factors Affecting Human Development, Washington, D. C.. 1969, P.A.H.O., pp. 199-201. Gabert, H. A., and Stenchever, M. A.: Electronic feral monitoring as a routine practice in an obstetric service: A progress report. AM. J. OBSTET. GYNECOL. 118: 534. 1974. Hammacher, K., Huter. K. A., Bokelmann. J., and Werners, P.H.: Foetal heart frequency and perinatal conditions of the fetus and newborn, Gynaecologia 166: 349, 1968. Hon, E. H.: Electronic evaluation of the fetal heart rate. AM. 1. OBSTET. GYNECOL. 83: 333, 1962.

June

I, 1976

4m. J. Obstet. Gynecol.

1 1. Neonatal conditions and the morbidity and mortality rates arc poor among prematures. 12. Postmatul,e infants have a significantly high incidence of perinatal mortality. 13. There seem to be characteristic FHR patterns indicating impending severe deterioration among postmature fetuses, particularly a combination of tachycardia. fixed baseline, and minimal decelerations. The author gratefully acknowledges the cooperation of Mr. Richard Blough, Senior Problem Analyst of the Biomedical (:omputation Facilities, University of Chicago, for pr,ogramming and statistical treatment of the data.

13. Hon, E. H.: .I’he classification of fetal heart rate, Obstet. Gynecol. 22: 137, 1963. 14. Hon. E. H.: Additional observations on “pathologic” bradycardia, AM. J. OBSTET. GYNECOL. 118: 428, 1974. 1.5. Hon, E. H., and Quilligan, E. J.: The classification of fetal heart rate, Corm. Med. 31: 779, 1967. 16. James. L. S.. Morishima, H. 0.. Daniel, S. S., Bowe. E. T., Cohen, N. H.. and Niemann, W. H.: Mechanism of late deceleration of the fetal heart rate. AM. J. OBSTET. GYNE~OL. 113: 578, 1972. 17. Joelsson, 1. and Westin, B.: Fetal heart rate during the third trimester of toxemic pregnancy and fetal distress before the onset of labor, Acta Obstet. Gynecol. Stand. 43: 338. 1964. 18. Kubli. F. W.. Hon, E. H., Khazin, A. F., and T’akemura, H.: Observations on the heart rate and pH on the human fetus during labor, AM. j. OBSTET. GYNECOL. 104: 1190, 1969. 19. Lee, C. Y., Di Loreto, P. C., and O’Lane,J. M.: A study of’ fetal heart rate acceleration patterns, Obstet. Gynecol. 45: 142, 197.5. 20. Low, J. A., Boston, R. W., and Pancham. S. R.: The role of fetal heart rate patterns in the recognition of fetal asphyxia with metabolic acidosis, AM. J. OBSTET. GYNECOL. 109: 922, 197 1. “I. Low, J. A., Pancham, S. R., Worthington, D., and Boston, R. W.: Clinical characteristics of pregnancies complicated by intrapartum asphyxia. AM. J. OBSTET. GYNECOL. 121: 452. 197.5. 22. Low, J. A., Pancham, S. R., Worthington, I)., and Boston. R. W.: The incidence of fetal asphyxia in six hundred high risk monitored patients, AM. J. OBSTET. GYNECOL. 121: 456, 1975. 23. Martin. C. B., Siassi, B., and Hon, E. H.: Fetal heart rate patterns and neonatal death in low birthweight infants, Obstet. Gynecol. 44: 503. 1974. 24. Mendez-Bauer, C., Poseiro, J. J., Arellano, G.. Zambrana, M. A., and Caldeyro-Barcia, R.: Effects of atropine on the human heart rate during labor, AM. .J. OBSTET. GYNECOL. 85: 1033, 1963. 25. Mendez-Bauer, C., Arnt, 1. C., Gulin, L., Escarcena, L., and Caldeyro-Barcia, R.: Relationship between blood pH and heart rate in the human fetus during labor, AM. .J. OBSTET. GYNECOL. 97: 530, 1967.

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125 3

26. Morishima, H. 0.. Glaser, B., Niemann, W. H., and James, L. S.: Increased uterine activity & fetal deterioration during maternal hyperthermia, AM. J. OBSTET. GYNECOL. 121: 531, 1975. brain damage and 27. Myers, R. E.: Two patterns of perinatal their conditions of occurrence, AM. J. OBSTET. GYNECOL. 112: 246, 1972. 28. O’Gureck, J. E., Roux, J. F., and Newman, M. R.: Neonatal depression and fetal heart rate patterns during labor, Obstet. Gynecol. 40: 347, 1972. fetal monitorinrr, Y, AM. ”1. OBSTET. 29. Paul. R. H.: Clinical GYNiCOL. 113: 573, 1972. 30. Paul, R. H., and Hon, E. H.: Clinical fetal monitoring. V. Effect on perinatal outcome, AM. J. OBSTET. GYNECOL. 118: 529, 1974. 31. Quilligan, E. J., Katigbak, E., and Hofschild, J.: Correlation of fetal heart rate patterns and blood gas values. II. Bradycardia, AM. J. OBSTET. GYNECOL. 91: 1123, 1965.

FHR patterns during labor. I 305

E. J., and Paul, R. H.: Fetal monitoring: Is it 32. Quilligan, worth it? Obstet. Gynecol. 45: 96, 1975. 33. Renou, P., Newman, N. W., and Wood, C.: Autonomic control of fetal heart rate, AM. J. OBSTET. GYNECOL. 105: 949, 1969. 34. Saling, E., and Schneider, D.: Biochemical supervision of the fetus during labor, J. Obstet. Gynecol. Br. Common W. 74: 799, 1967. 35. Shenker, L.: Clinical experience with fetal heart rate monitoring of one thousand patients in labor, AM. J. OBSTET.GYNECOL. 115: 1111, 1973. 36. Swartwout, J. R., Campbell, W. E., and Williams, L. G.: Observations on the fetal heart rate, AM. 1. OBSTET. GYNECOL. 82: 301, 1961. 37. Wood. C.: Use of fetal blood samnline and fetal heart rate monitoring, in Adamson, K., iditor: Diagnosis and treatment of fetal disorders, New York, 1968, SpringerVerlag, pp. 163-174. ”