British Journal of Obstetrics und Gynaecology

December 1975. Vol82. pp 943-951

PROGRESSION IN RESPONSE PATTERNS OF FETAL HEART RATE THROUGHOUT LABOUR BY

D. T. Y. LIU, Research Fellow and Lecturer G. THOMAS, Lecturer AND

R. J. BLACKWELL, Principal Physicist Department of Obstetrics and Gynaecology University College Hospital, London Summary A study of 70 fetal heart rate (FHR) traces throughout labour has allowed analysis of FHR responses aseociated with approximately 7000 individual uterine contractions. The significance of the less emphasized FHR patterns has been assessed and an attempt has been made to identify any trend or progression in the occurrence of these patterns. Transient acceleration was the most frequently occurring response in early labour and was the first observed response in the majority of cases. Decelerations became prevalent as labour progressed. A hypothesis is proposed to explain the observed overall progression in FHR responses and the possible physiological mechanisms underlying the cyclic changes in response patterns which occur throughout the course of labour.

INTRAPARTUM fetal monitoring depends on assessment of the significance of fetal heart rate (FHR) responses during and between uterine contractions. Following the original description of classical response patterns by Hon (1968) there have been additional reports of significant patterns (Beard et al, 1971; Shelley and Tipton, 1971; Goodlin and Lowe, 1974). It is becoming increasingly clear that many different FHR response patterns are present in labour and that the clear interpretation of FHR traces would be easier if it were possible to elucidate the significance of the less common FHR responses. In this study an attempt has been made to determine their significance and to identify any trend or progression in their occurrence which may be of predictive value.

January 1973 and June 1974 and each fulfilled the criterion of having been monitored throughout established labour to within 5 minutes of delivery, using a Hewlett Packard cardiotocograph (HP 8025A). Monitoring was limited to “at risk” fetuses, as defined by Beard et a1 (1971), and to fetuses demonstrating clinical signs of distress. FHR tracings were taken directly from a scalp or spiral electrode and uterine contractions were registered by external tocography or intrauterine pressure measurements. A code, which is shown in Table I, was prepared to represent ten major FHR responses to contractions, the delay in response time and the basal rate and baseline variability between responses. The traces were then analyzed progressively contraction by contraction. This made it possible to determine the prevalence of each of the response patterns and to determine any pattern progressions which might occur.

AND METHODS MATERIALS The 70 patients in this study were delivered at University College Obstetric Hospital between

943

944

I N , THOMAS AND BLACKWELL TABLEI Definition and description of fetal heart rate response patterns observed in the 70 traces Basal conditions

Types

Baseline variability

Basal fetal heart rate (between contractions)

Patterns of response to contractions

Description

Silent Normal Saltatory

Fluctuates less than five beats interval difference Range between 5 and 25 beats interval difference In excess of 25 beats interval difference

Bradycardia Normal Tachycardia

Less than 100 beats per minute 120 to 160 beats per minute In excess of 160 beats per minute Descriptions

Types

I Normal

Basal rate of 120 to 160 per minute, baseline variation between 5 and 25 beats interval. No change with contractions ~

~

11 Transient acceleration

~~~

Transient increase in rate of more than 10 beats lasting 30 seconds or more

~

I11 Pre-acceleration dip

Initial acceleration of more than 10 beats followed by deceleration

I V Pre-acceleration deceleration and rebound

V Early deceleration

Similar to I11 with a rebound acceleration exceeding 10 beats above baseline

A pure deceleration lasting 30 seconds or more

Y b Late deceleration

Pattern similar to V except nadir is delayed with regard to peak of uterine contraction by 30 seconds or more

VI Block deceleration

Large steep deceleration lasting more than 30 seconds and characterized by flat troughs

VII Prolonged deceleration

Deep deceleratim which recovers slowly through a few contractions

Deceleration and rebound

Rebound of at least 10 beats above baseline after deceleration

~

\'I11

IX Saltatory response pattern

Infants with a one-minute Apgar score of 6 or below were then compared with the high Apgar group with respect to these prevalences and pattern progressions. Five minute and 15 minute segments of FHR trace demonstrating constant response patterns were then sought and the respective incidences in the low and high Apgar groups were compared. Similarly, the characteristics of basal fetal heart rate and baseline variability in the two groups were compared.

~~~~

____

-

Large acceleration and deceleration differing from saltation in its excursions bsing spread over 30 seconds or more

The respective incidences of early and late decelerations and the timing of their appearance in relation to the time of delivery were compared in the two groups of newborn babies. RESULTS Twenty-two of the 70 monitored fetuses (31.5 per cent) had an Apgar score of less than 7 at one minute. Only in two of these was the Apgar score less than 8 at five minutes. There was no significant difference in the

FETAL HEART RATE IN LABOUR

100

HIGH A N D LOW APGAR n=70

90-

80-

__9

8

--

7

6

5

4

,

3

2

1

0

Hours before delivery

9

8

7

6

5

4

3

2

1

0

Hours before delivery M

no change

@[email protected]

accelerations

+----+

decelerations

FIG1 Showing the percentage distribution of fetal heart rate response, comparing the overall group with the low Apgar group.

945

946

LIU, THOMAS AND BLACKWELL

exception that the incidence of transient accelerations was marginally lower in the first half of labour and the rise in incidence of pure decelerations tended to occur earlier, ie 64 hours as opposed to 5 hours before delivery (Fig 1).

management of the two groups of patients. The number of uterine contractions per half hour was similar in the two groups. There was a mean of 11 contractions per half hour in early labour and this increased to 13 during the second stage. Transient FHR changes in response to uterine contractions were present in all tracings and early decelerations were recorded at some time during each of the 70 labours in the study. Distribution of response patterns In early established labour approximately 60 per cent of traces were without transient FHR responses. This percentage decreased as labour progressed until one hour before delivery when only 12 per cent showed no FHR changes (Fig 1). The first observed response to contractions in 78 per cent (55/70) of patients was a transient acceleration. The incidence of transient accelerations fell gradually during the course of labour. The incidence of pure decelerations was low in early labour but increased gradually to reach levels equal to transient accelerations (10 to 15 per cent), three to four hours before delivery. There was a sharp increase in the incidence of decelerations in the last 90 minutes of labour. Each of the remaining FHR response patterns occurred in association with between 5 and 10 per cent of contractions but there were no obvious trends in incidence. The distribution of response patterns in the low Apgar group was similar to the overall distribution shown in Figure 1, with the

Five minute segment analysis (Table 11) Five minute segments of FHR trace demonstrating only transient accelerations were more frequent in the high Apgar group of fetuses (p = ~ 0 . 1 ) .Segments of late decelerations and block decelerations (pattern VI) were more often associated with the low Apgar group (p = t o -1 and ( 0 . 0 5 respectively). Only one episode of protracted deceleration (pattern VII) occurred in this study. Fijleen minute segment analysis Fifteen minute segments of trace in which only one type of response pattern was seen occurred much less frequently than did five minute segments. Fifteen minute segments of patterns other than early decelerations, late decelerations and transient accelerations were very uncommon. Those segments demonstrating early decelerations and those showing transient accelerations occurred with similar frequency. In the high Apgar group, 30 fetuses (62.5 per cent) demonstrated fifteen minute segments of early decelerations compared with 15 fetuses (68.1 per cent) in the low Apgar group. Similarly 12 high Apgar fetuses (25 per cent) demonstrated fifteen minute segments of transient accelerations compared with five fetuses (22.7 per cent) in the

TABLEI1 The signf$cance of jive minute segments of constant response pattern in the Patients in low Apgar group

Patterns of fetal heart rate response

two groups of'infants

Patients in high Apgar group

Number

Per cent

Number

Per cent

I1

18

81.8

47

97.9

I11 IV V

18 12 22

81.8 54.5 100.0

35 21 48

72.9 43.8 100.0

10

45.5

10

20.8

Vb

VI VIII

9

40.9

I

14.6

9

IX

16

40.9 72.7

19 31

39.6 64.6

Significance using chi-square

FETAL HEART RATE IN LABOUR

947

through transient acceleration to a third pattern is shown in Table IV. Early deceleration, saltatory responses and pre-acceleration dips were seen to follow transient accelerations in decreasing order of incidence. The trend, normal to transient acceleration to pre-acceleration with deceleration was significantly more common in the low Apgar group (p = t0.05) whilst the progression of normal to transient acceleration to saltatory response was significantly more common in the high Apgar group (p = (0.1). In view of the number of labours studied, it became impractical to continue this serial method of progression analysis. The distribution of response patterns following pre-acceleration with deceleration, early deceleration and saltatory response was analyzed and tabulated (Table V). Pre-accelerations with deceleration were most commonly followed by early decelerations as were saltatory response patterns. Early decelerations were most commonly followed by transient accelerations. Frequent alternations between early and late decelerations occurred in both groups of fetuses.

low Apgar group. The differences between these respective incidences are not significant. Fifteen minute segments of late decelerations were present in 14 high Apgar fetuses (29.2 per cent) and nine low Apgar fetuses (40.9 per cent). This difference is not significant. Progressions Table 111 shows the distribution of response patterns which were seen to occur immediately after a normal trace and compares the respective incidences in the high and low Apgar groups. Transient accelerations were the most commonly occurring first response patterns (52 8 per cent). Early decelerations were observed as the first patterns in 20 per cent of fetuses whilst the incidence of each of the remaining patterns as a first response was less than 10 per cent. There was no apparent relationship between the nature of the first FHR response and one minute Apgar score. An attempt to assess possible significance in progression of response patterns from normal

TABLEIll Types of first response pattern following a normal trace in the two groups of infants Number of patients

Type of first response pattern following a normal trace Pattern I Pattern I Pattern I Pattern I Pattern I Pattern I Pattern I

Total

Pattern I1 Pattern V Pattern I11 + Pattern IV + Pattern IX + Pattern VI + Pattern VIII +

37

--z +

14 7 5 5 1 1

Low Apgar High Apgar 11 5 I 2 2 1

26 9 6 3 3

-

1

-

TABLEIV Progression of response patterns through transient acceleration in the two groups of infants Number of patients Progress in patterns of response PatternI-+II-+

~

Significance by High Apgar chi-square

Total

Low Apgar

V

14

5

9 9

Pattern I -+

I1 -+

IX

9

0

Pattern I --+

I1-+

I11

1

5

Pattern I -+ Pattern I -+

I1 -+ I1 -+

IV VIII

6

1 0

1

5 1

-

x2 = 3.2 p c =

Progression in response patterns of fetal heart rate throughout labour.

A study of 70 fetal heart rate (FHR) traces throughout labour has allowed analysis of FHR responses associated with approximately 7000 individual uter...
547KB Sizes 0 Downloads 0 Views