The incidence of intrapartum fetal distress with advancing gestational age

FETUS,PLACENTA, ANDNEWBORN

The incidence of intrapartum fetal distress with advancing gestational age HENRY

KLAPHOLZ,

EMANUEL

A.

M.E.E., FRIEDMAN,

M.D. M.D.,

MED.SC.D.

Mn.wrhtwtt\

Boston,

A total

oj 679 @al monitoring wcords uvrc carrlfully rwicwc~d in ordcr to dc&rmino th(’ incidrvw o/ occurr(w e of latcj and z~ariablr dw&ration pattcdrns with wsprct to advancing gc~stational ago. No stutistic.all~ .signt$cant incwase in occurwaco (f thcw patterns could bc cl&v-tad in gc’stations that progrwod beyond 42 uweks. Thcz prwio usly hold conccp that routiw prophylactic. intcvwntion in g&ations 42 woks or mow must br challenged. (AM. J. OBSTET. GYNECOL. 127: 405, 1977.)

of

THL SUSCEPTIBILITY of the postterm fetus to distress in labor has come to be accepted as fact. The nominal period of 41 or 42 weeks after the last menstrual period is often used as an arbitrary guide for therapeutic intervention in otherwise uneventful ongoing pregnancies. A widespread practice has developed of terminating the pregnancies of certain classes of lvomen for medical reasons such as diabetes mellitus by induction of labor and even by cesarean section. Justification for this is based on statistical studies showing that these pregnancies will fare poorly if permitted to In addition, claims have been proceed past “term.“’ made that it is reasonable to terminate all postdate pregnancies because the incidence of fetal distress rises in otherwise normal gestations if such pregnancies are allowed to continue.” It is inferred. but not demonstrated, that the risks of the development of subsequent intrauterine hypoxia far out-

From Israel RecPriwd

the D$artmmt Hospital and /or

of Of)stctric~ and Gprcology, Harzwd Medical School. 20,

1976.

Rrpr~nf rcyrmts: Hmty iilaphol:, .$Yv.. Brutort, Massachwcrtt.c 02215.

M.D.,

Re,z&d

Augmt

Arcrptrd

A~ipt

puhlicatiorl

ilpr-il

weigh any potential hazards of induction of labor or cesarean section. Prior to the advent of electronic fetal heart rate (FHR) monitoring, physicians had little on which to base a diagnosis of fetal distress exe ept transient drops in heart rate perceived by auscultation and perhaps the appearance of meconium in the amniotic. fluid. We now know that neither of these criteria is adequate to diagnose fetal hypoxia. ‘L ’ F*p isodes of intrauterine hypoxia can now be readily recognized as they arise bl the appearance of FHR patterns that are considered to be specific and perhaps pathognomonic. \Ve thus have at hand means whereby we may more accurately cletermine if indeed the incidence of FHR patterns of distress is in any way related to advaming gestational age.

Methods and materials Electronic FHR monitoring is performed routinely at Beth Israel Hospital on essentially every obstetric patient, whenever feasible. and on all high-risk patients. Of the 1,050 patients delivered from January 1, 1975, through June, 30, 1975, 707 (67.3 per cent) had FHR monitor records of sufficient quality to permit meaningful interpretation. Of these 679 (96.0 per cent)

Beth

2, 1976. 24,

1976. 330

Brooklinr

405

406

Klapholz

Table

I.

monitored

and Friedman

Distribution series

by gestational

age for total and

found (61.5

36-37 38.YY 40-4 1 42-43 44+ Total

77 233 ,569 97 12 988 --

7.8 23.6 5i.6 9.8 1.2 100.0

*Percentages calculated

57 127 413 70 12 679

x.4 18.7 60.8 10.3 1.8 100.0

vertically

to yield

74.0 54.5 72.6 72.2 100.0 68.7 gestational

age

distribution. tpercentages of monitoring

by a single

terpret

calculated horizontally within each gestational

to indicate age group.

frequenq

FHK per

Classification

II.

of fetal heart rate patterns

tent)

Table

III.

oxytocin

i\,hat

anesthesia

and

No. 36-37 38-39 40-4 1 42-43 44+ Total

57 127 413 70 12 679

71.9 66.1 77.3 65.i

31.6 27.6 32.0 35.7

The

distribution

of

gestational

ages

mc~nitore(l

usiiig

the

inrcl-real

peridural

block

Mith

c.it1tc.r

a ~audal

or

more

frequently

(Table

Ill).

although

this

I\;,\

Results

were 36 or more weeks’ gestational age; this group constituted the study population. Gestational ages were computed to the nearest week according to each patient’s reported date of last menstrual period or, if this was unknown or unacceptable, to ultrasonographic cephalometry.

10 in-

not statistically significant (I = 0.89 for pcridura~ an~‘bthesia. t = 0.70 for oxytvcin). No alterations in the usual obstetric management policies 11crc’ made mcrch because of gestational age. Intervention 11 as undertaken if irremediable fetal distress sul~c’r~c~~~d OI if ni;iternal or obstetrical considerations die tnted it. Since f&al outcome mav ottrn be inf-luenc et1 h) (11, this study tocuscs mode of delivery, e.g., midfi)rceps. only upon the appearance of tetal distress during labox and not on any subsequent perinatal morbidity.’

<30 b.p.m. drop 31-70 b.p.m. drop >70 b.p.m. drop

Frequency of peridural in study group

wet-c

conlpetei~t

lumbar approach. Oxytocin \\as employed as ncetlctl according to the obstetric, situation. Both oqtoc in ancl conduction anesthesia Iverc uniformly distrihutctl in the sexera gestational age groups, except in those o1’J I weeks or more where their ust’ tended to occur wnw

l’cknhlc~ d~,rr,L,~cctio,l.~: Mild ~30 b.p.m. drop and ~30 sec. duration Moderate 3 l-70 b.p.m. drop or 3 l-45 sec. duration SCWTC >70 b.p.m. drop or rate <60 b.p.m. or ~4.5 sec. duration Latr /fKdrr/lltoll\: Mild Moderate Severe

deemed

In this serials .+10 l)ati(,tlt\

method alone and (37 patktits ( 14.9 pvr ~111) u VI I, monitored b7 means of ttir, estcrnal ulrrasoutid, tocodvn;lmometcr method. I‘hr rcmaindcr ot 1lit study patients were monitored using ;I cc,mbination of external and internal tee hnicluw Ke~ords \\crc’ PI-c,duced on Hewlett-Packard Model HK?OA cardiotocograph (Hewlett-Packard. lnc ., Palo .AIto. (Xiforrlial and Corometrics Models 101. 10 1A. and 101 13 fetal heart rate monitors (Coron1etric.s Medical SFstenl4. Wallingford, Connecticut). Periodic de, elrratiollx iI1 fetal heart rate l\ere tlassihcd according to the, outline in ‘l‘able I I. Anesthesia. if request&. \\as usually administer~cl a’r a continuous

Table

individual

recordings.

in

the study group (Table I) was essentially the same as the distribution of pregnancy duration in the over-all gravid population from which they were drawn. Moreover, the relative incidence of monitoring within each gestational age division was fairly constant, except in the small group of patients exceeding 43 weeks. all of whom were monitored. The FHK records of these patients were carefully pertlsed and classified according to abnormalities

Variahle decelerations or cord compression patttrm were encountered during the course of‘ the monitored labors in 439 gravidas in this series for a total incidence of 66.1 per cent (Table IV). Stratifying the pregnancies by gestational age into 2 peek intervals. we find the incidence of occurrence of variable decelerations to he fairly constant. Similarly. the frequency of moderatr plus severe variable decelerations, as well as of sevcw only, is not very different betlteen groups. The pobtterm group appears to exhihit the same incidcncc as does the group of patients delkcred carlier. ‘There is no clear-cut trend that advancing gestational age is associated with higher frequency of variable decelerations. The

incident-e

insufficiency

identified cent

were

of late decelerations patterns

was

in 166 labors considered

24.4

(Table

sevcrc

and

or uteroplacental per

cent,

having

hew

V). Of‘ these. 8.1 peg 9.1 pc’r cent

modcratc

Volume Number

127 4

Table

IV.

patterns

lntrapartum

Incidence of variable by gestational age

36-37 38-39 40-4 1 42-43 44+ 42+ Total

1;;r113 70 12 82 679

deceleration

66.7 64.6 68.3 67.1 66.7 67.1 66.1

FHK

Table patterns

57.9 55.9 60.0 54.3 66.7 56.1 58.6

40.0 41.7 37.5 40.0 58.3 42.7 39.2

in nature. .-\s in the case of variable decelerations. no significant difference in occurrence rates between gestational age groups could be appreciated. The postterm group. consisting of all gestations of 42 weeks’ duration 01. longer, actually experienced a somewhat smaller incidence of severe late decelerations (6.1 per cent) than did the remaining patients with shorter gestational ages (8.4 per cent), although this difference was not statistically significant (t = 0.80).

Conclusion Based OII these data it would appear that previously stated concerns regarding the special intolerance of the postterm fetus to labor was not confirmed. In view of the fat-t that the total sample of patients included diabetic, hypertensive, anemic, and otherwise “at risk” patients as well as normal subjects (more or less evenly distributed by gestational age), it is surprising that the anticipated fetal distress seen in these high-risk groups \\as not encountered in the o\:er-all figures. In addi-

fetal distress

V.

with advancing

gestational

Frecluencl; of‘ late decelrration bp gestarional age

36-37 38-39 40-4 I 42-43 ‘M+ 4”+ Total

57 18 413 70 12 82 679

31.6 18.9 24.7 25.7 33.3 26.X 24.4

21.1 15.0 16.7 21.4 8.3 19.i 17.1

age

407

FHK

r, .:3 i.9 X.1) i.1 0.0 6. I 8.1

tion, umbilical cord problems, logically expected to occur more frequently in premature labors because of generally poorer apposition of the presenting part to the cervix and more tommon occurrence of malpresentations, were not sc’en u ith ally greater incidence among patients delivered earl\: than those dcliwring at or beyond term. The most prudent course of action that u~uld be recommended Lvhen dealing with a postterm gra\ida in labor would be to treat her as one xvould treat any other laboring patient, individualizing according to need. maintaining appropriate vigilance. and intervening only when the fetal heart rate monitor indicates the actual presence of fetal distress. There is little to,justif) aggressive forms of intervention at or beyond term on a “ prophylactic” basis in anticipation of unforeseen intrauterine hypoxic problems in the patient who tlcmonstrates no objet tive evidence of a medical tliswse process or obstetric disorder warranting such interwntion.

REFERENCES

1. Hagbard. L.: Pregnancy and Diabetes Mellitus, field, Illinois. 1961, Charles C Thomas, Publisher. 2. Vorherr, H.: Placental insufficiency in relation

term pregnancy and fetal postmaturity

Springto post-

evaluation of feto-

placental function; management of the post-term gravida. AM. J. ORSTET. GYNECOL. 123: 67. 1975. 3. Miller, F. C.. Sacks, D. A.. Yeh, S.. et al.: Significance of

meconium during labor, AM. J. 0~sx.r. GYNLCOL. 122: 573. 1975. 4. Benson. R. C., Shubeck. F., Deutschberger, J., et al.: Fetal heart rate as a predictor of fetal distress, Obstet. Gynecol. 32: 259, 196X. 5. Friedman, E. A.: Patterns of labor as indicators of risk. Clin. Obstet. Gynecol. 16: 172. 1973.