EUROP. J. OBSTET. GYNEC. REPROD. BIOL., 1979,9/S, @Elsevier/North-I-IoIland Biomedical Press
307-312
Comparison of two successive policies of cervical cerclage for the prevention of pre-term birth P. Lazar, B. Servent, J. Dreyfus, S. Gueguen and E. Papiernik Unit6de&&r&s de Midecine
Epiddmiologiques
de Paris&d,
et Statistiques SW I’Environnement
et la Sant6, Centre Hospitalier de Haguenau, Faculte’
France
Accepted for publication 9 March 1979 LAZAR, P., SERVENT, B., DREYFUS, J., GUEGUEN, S. and PAPIERNIK, E. (1979): Comparison of two successive policies of cervical cerclage for the prevention of pre-term birth. Europ. J. Obstet. Gynec. reprod. Biol., 9/5, 307-312. The percentage of women receiving cervical cerclage increased from 5% to 18% between two periods at Haguenau maternity hospital, according to a new policy for the prevention of pre-term birth. A parallel reduction of premature deliveries by about a half was observed in the relevant group of women. This suggests that cerclage might be employed on another basis than is currently the case, and that a randomized trial is urgently needed to define its indications more precisely. high-risk pregnancy; cervical incompetence;
cervical cerclage; prevention; prematurity _.-____-.
-.-.-___-
_____
suture (Dumont and Poizat, 1974). However, none of these proposals have involved use of the procedure in more than 2-3% of all pregnancies. Since 1971, cervical cerclage has been deliberately employed in a higher percentage of pregnancies than usual in Haguenau maternity hospital. In the period 1971-72, the rate of cerclage among women first consulting before the 29th wk of gestation was 5%, but, in 1973-74, it was increased to 18%. We have compared the rate of pre-term deliveries in these two periods and attempted to relate the difference to the different rates of cerclage. This study is of particular interest, as no controlled trials have been yet conducted to evaluate the effect of this treatment on pre-term delivery (Lancet, 1977). Obviously it cannot replace a trial, but it can show to which extent such a trial is needed and ethically justified.
Introduction
The traditional indications for a cervical cerclage to prevent pre-term delivery are either constitutional cervical incompetence of congenital or traumatic origin (diagnosed prior to pregnancy by hysterography or by clinical calibration of the cervix), or functional incompetence, usually indicated by a previous abortion late in pregnancy (Hervet and Huguier, 1961). Generally less than 1% of pregnant women have such indications. Various authors have proposed extending the use of this procedure to include women with less severe congenital and traumatic anomalies (SrketiC et al., 1975), or functional insufficiencies (Widmaier and Reichardt, 1973), or have suggested performing the intervention beyond the 16th wk of gestation up to the third trimester of pregnancy. Other authors have derived scoring systems to combine the various risk factors to assess eligibility for 307
308
P. Lazar et al.: Cervical cerclage and pre-term birth
Methods
was 5.2% in the first period and 18.3% in the second. The rate of pre-term deliveries was IS% smaller in period II, but this difference is not statistically significant. The marked difference in the rate of prematurity in the two periods among women with a cerclage is not by itself meaningful, since a higher proportion of women were operated on in period II, and women will have been included who were, on average, at lower risk of a premature delivery. The women were classified into high, intermediate and low risk groups for prematurity (as discussed above) as follows: (1) The percentage of “high-risk women” was taken as the percentage operated on in the first period (5.2%). The numbers of such women in the two periods are then 47 and 6 1, respectively. (2) The percentage of “low-risk women” was taken as the percentage not operated on in the second period (81.7%). The numbers of such women in the two periods are then 741 and 963, respectively. (3) The number of “intermediate-risk women” in each period may be obtained by subtraction and are 118 and 154, respectively. We must then select from the 859 women who did not have a cerclage in period I, the 118 who would have been expected to have had a cerclage if they had presented during period II and, symmetrically, we have to select, from the 215 women who had a cerclage in period II, the 154 who would have been expected not to have had a cerclage had they presented during period I. This was achieved thus: (a) Considering only the women presenting in period II, we constructed a discriminant equation based upon prematurity risk factors to distinguish between women who had and did not have a cerclage. (b) A score was calculated from the discriminant equation for each of the 859 women who were not
The present study includes all women having a singleton birth between February 1971 and December 1974, who had at least one examination in Haguenau maternity hospital before the 29th wk of gestation; 906 women fulfilled these criteria in the first period (1971-72) and 1178 in the second (1973-74). A birth was regarded as pre-term if delivery occurred before 37 wk of gestation. For each of these two periods we have classified the women into 3 categories: the first being those women who would have had a cerclage if they had presented in either period (“high-risk women”), the second being women who would not have been liable for cerclage had they presented in either period (‘low-risk women”), and the third being those women who would have been given a cerclage if they had presented in the second period but would not have had one if they had presented in the first period (“intermediate-risk women”). This means that, using the major change having occurred in the policy, we have been able to identify -which is unusual in such “historical” comparisons -two groups as comparable as possible between the two periods, with and without the treatment under analysis. After making this classification, prematurity rates have been compared between the two periods in the 3 categories. The classification procedure (which will be described together with the results) is based upon the statistical method of discriminant analysis (Anderson, 1958). Results
Table I shows the rates of cerclage and pre-term birth in the two study periods. The rate of cerclage
TABLE I
Description of the populations in periods I and II
Period
I II Significance NS = not signikant.
No. of cases
906 1178
% of women given sutures
5.2 18.3 P < 0.001
% of premature deliveries
8.5 7.0 NS
% of premature deliveries among women With a suture
Without a suture
23.4 10.7 P = 0.05
1.1 6.2 NS
309
P. Lazar et al.: Cervical cerclage and pre-term birth TABLE II
Predictive variables corresponding suture and scoring weights % of women with suture when the sign is present
Variable
rates
of
Scoring weight Period I
Period II
Period I
Period II
Medical history late abortion prematurity other ’
19 19 23
30 25 27
0.19 0.17 0.30
0.17 0.02 0.08
Present pregnancy open cervix short cervix
16 20
41 44
0.06 0.28
0.10 0.63
’ Primiparous aged more than 35 yr, treated sterility, uterine malformation, placenta previa.
given a cerclage in period I, and the 118 with the highest scores were designated as the “intermediaterisk” group. (c) The symmetrical procedure was applied to define the 154 “intermediate-risk” women in period II. Table II shows the variables used in the discriminant analysis and their weights within each period. Table III shows the rates of prematurity in the 6 defined groups. The prematurity rate in the second period is significantly lower within the “intermediaterisk” group of women but the differences among “high” and ‘low” risk women are not significant. These findings are consistent with a cervical cerclage protecting against premature delivery among the “intermediate-risk” group. However, the reconstituted decision rules are
TABLE III Period
Rates of prematurity in the 6 groups High-risk women
Intermediate-risk women
Low-risk women
=
#
I
g = 23.4%
118 -
II
g=
#4 = 7.1%
$& = 6.2%
Significance
NS
P = 0.01
NS
19.7%
- 19.4%
=
5.8%
obviously approximate, and it is important to consider how these might affect the conclusions. The variables used for predicting which women would have been sutured are practically the same as those which would be used to predict prematurity, and it is possible that the observed prematurity rates of 19.4% and 7.1% in the intermediate category are seriously biased (the former being too high, the later too low). An argument against this is provided by the observation of no marked difference between the corresponding rates in “high-risk” women (23.4% and 19.7%, respectively) and “low-risk” women (6.2% and 5.8%, respectively). Another argument comes from the comparison of the main risk factors of pre-term birth (previous late abortions or pre-term birth, metrorrhagia, short or open cervix in the present pregnancy) between the two periods in the intermediate group. Table IV shows that there is no major difference between the two groups, except for previous pre-term birth, which is more frequent in period I, and opening of the cervix, which is more frequent in period II. However, it is possible to take all the risk factors directly into account by calculating a risk score through a discriminant analysis, weighting the various factors predictive of pre-term birth (Papiernik and Kaminski, 1974).
TABLE IV
Main risk factors in the intermediate-risk of the two periods (%) Period I (n = 118)
Previous late abortion Previous pre-term birth First examination of the present pregnancy metrorrhagia short cervix open cervix Examination between 19 and 24 wk metrorrhagia short cervix open cervix Examination between 25 and 28 wk metrorrhagia short cervix open cervix
groups
Period II (n = 154)
3.4 17.8
2.0 2.6
7.6 5.9 0
4.5 4.5 3.0
5.1 11.9 0
5.2 12.2 2.6
3.9
4.1 21.3 9.8
15.6 0
P. Lazar et al.: Cervicalcerclage and pre-term birth
310 TABLE V
Mean values of a prematurity index (m f SE)
Period
High-risk women
Intermediate-risk
I
2.62* 0.41 41
1.51 f 0.20 118
1.03 f 0.06 741
1.18 + 0.06 906
II
2.25 f 0.25 61
1.25 f 0.15 154
1.22 f 0.05 963
1.28 f 0.05 1178
Significance
NS
NS
P = 0.02
P = 0.08
TABLE VI Period
I II Rates ratio (II/I)
Standardized rates of prematurity High-risk women
Intermediate-risk women
women
20.2% 18.1% 0.9
19.2% 1.1% 0.4
6.1% 6.1% 1.0
Low-risk
Table V gives the mean values of this index in the 6 groups. The overall difference between the two periods - the women presenting in period II being apparently at a greater risk - is significant in low-risk women only. Standardized rates of prematurity were calculated, taking the cumulated distribution of risk scores in the two periods as a standard. Table VI shows the standardized rates and their ratio. This ratio is close to 1 in the two extreme categories and much reduced (by more than a half) in the intermediate-risk category.
Discussion
The percentage of women receiving cervical cerclage increased from 5% to 18% between 197 l72 and 1973 at Haguenau hospital. When this change took place a system for scoring prematurity risk was introduced into the hospital protocols. Table II indicates how the clinical signs were taken into account before and after the change of policy. Generally, during period II, a heavier weight was given to any risk factor and, in particular, opening and shortening of the cervix were considered as major risk factors. More than 40% of women presenting with either of these signs before the 29th wk of gestation were
women
Low-risk women
Total sample
operated upon, whereas the corresponding rate was less than 20% in the first period. Very little is demonstrated of the effect of cervical cerclage in preventing premature deliveries, and no controlled trials of this procedure have been reported. Studies on women with a definite cervical incompetence have compared results of previous pregnancies of the operated women to those after treatment (Hervet and Huguier, 1961; Carollo, 1975), finding obvious and convincing differences, particularly in the reduction of late abortions. Such considerations have been used as an argument for widening the indications for such suture. Other workers (Fournil et al., 1977) have proposed reducing the proportion of women given a cerclage on the basis of a cervix calibration during the first trimester of pregnancy, but their study included no appropriate control group. The major change of policy which occurred in Haguenau hospital has allowed us to study directly the protective effect of a cervical cerclage against premature delivery by enabling us to compare two groups of women likely to be similar. As indicated in Tables III and VI, a reduction by a factor of at least 2 has been observed in the prematurity rate among women from whom a suture was performed in period II (13% of the women consulting before the 29th wk of gestation). We cannot explain this reduction by a general change in the risk factors among women presenting in the two periods, nor by an obvious bias in the definition of the groups cornpared in periods I and II. However, the increase in the frequency of sutures is not the only therapeutic difference between the two periods. In particular, the number of medical examinations also increased, as did the frequency of hospital admissions for causes other than cerclage, and the reduction in prematurity could be related to a better surveillance and treat-
311
P. Lazar et al,: Cervicalcerclage and pre-term birth TABLE VII
p-Mimetics
Not used Used
Prematurity rate in period II according to the use of p-mimetics ’ High-risk women
Intermediate-risk women
Low-risk women
10.2% 49
4.2% 119
4.6% 814
26.3% 19
42.9% 28
60.0% 10
1 Unknown for a small percentage of women.
ment during pregnancy. However, if such was the case, a general decrease in the rate of premature deliveries would have been expected, and not only in the category of “intermediate-risk” women, since the increase in examination frequency occurred among all women, even if it looks to be higher in the intermediate-risk group (Table VIII). Moreover, for the intermediate-risk women, the difference of prematurity between the two periods was not related to the number of consultations between the 29th and 37th wk of pregnancy. Anyway, it is obviously impossible to disregard completely the hypothesis that the observed difference, in the intermediate group, might be related to the special attention devoted to women with a cerclage in period II. The benefit then would be only a “side-effect” of cerclage. The greater use of /3-mimetics during period II raises a somewhat different problem, since there is no comparative point during period I when such drugs were not used. Table VII gives the available information for period II. The use of fl-mimetics was relatively rare (14% among intermediate-risk women) and was apparently of limited efficiency, since the rate of prematurity, when these drugs had to be used, was quite high: about 40% on average. However, it is obviously impossible to exclude the possibility that
TABLE VIII Percentage of hospital admissions for causes other than cerclage (29-36 gestational wk) Period
I
II Significance
High-risk women 25% 55% P < 0.001
Intermediate-risk women
Low-risk women
17% 67% P < 0.001
4% 10% P < 0.001
TABLE IX
Rate of premature deliveries in the intermediate risk category according to the prematurity risk index
Period
Value of prematurity risk index
Total
Low 1
High ’
I
13.8% 58
25.0% 60
19.4% 118
II
2.4% 82
12.5% 72
7.1% 154
0.2
0.5
0.4
Rates ratio (II/I)
i The distribution was divided at its median.
tocolytic agents contributed significantly to reducing the risk of pre-term delivery, especially in the intermediate group, either through a positive interaction with cerclage or just because, with a suture in place, the physicians used them at a higher dose or with a different pattern. In Table IX we have divided the women in the intermediate-risk group into two categories on the basis of the prematurity risk index. Cerclage looks to be of value to both those with the high- and low-risk scores within this intermediate group. Finally, our findings suggest that the increased rate of cervical cerclages in Haguenau from 1973 might have reduced the rate of premature deliveries among the new women treated by about a half, either because of the cerclage itself or due to any of the associated therapeutic attitudes. A cooperative randomized trial is then urgently needed which will enable the balance of costs and benefits of this procedure to be better assessed, as well as enabling the indications for the operation itself to be defined more precisely.
Acknowledgements
We are greatly indebted to Dr. Peter G. Smith for his help in English translation. This work was supported by grants from the Institut National de la Sante et de la Recherche Medicale, Ministere de la Sante Mutuelle GBnCrale de 1’Education Nationale and Groupe d’Etude de la PrCmaturitC et de la Souffrance Perinatale.
312 References Anderson, T.W. (1958): An Introduction to Multivariate StatisticalAnalysis, Ch. 6. Wiley, New York. Carollo, F. (1975): Closure of dilated cervix during pregnancy for prevention of premature delivery. In: Perinatal Medicine, 4th Europ. Congr..August 1974, p. 279. Editors: Z.K. Stembera, K. PolaEek and V. gabata, Georg Thieme, Stuttgart. Dumont, M. and Poizat, Cl. (1974): Etude d’un coefficient d’appreciation de la beance cervico-isthmique. A propos de 50 observations de beances trait&es par cerclage. J. Gynkc. Obste’t.Biol. reprod., 3, 981. Fournil, C., Hidden, J. and Lajoux, P. (1977): Evaluation du calibre de l’isthme u&in en debut de grossesse. Int&6t dans l’indication du cerclage du col. 134 Observations. Nouv. Presse m&d., 6, 5 23.
P. Lazar et al,: Cervicalcerclage and pre-term birth Hervet, E. and Huguier, J. (1961): B&race cervico-isthmique. Bull. F&d. Sot. Gynk. Obsttft.,13, 1-17. Lancet (1977): The Shirodkar Stitch (leading article). Lance& 1, 691. Papiernik, E. and Kaminski, M. (1974): Multifactorial study of the risk of prematurity at 32 weeks of gestation. 1. A study of the frequency of 30 predictive characteristics.J. perinat. Med., 2, 30. SrketiL, M., Salamon, B. and Peri& D. (1975): Cervical cerclage as the prevention of premature delivery. In: Perinatal Medicine, fth Europ. Congr., August” 1974, p. 281. Editors: Z.K. Stembera, K. PollEek and V. Sabata. Georg Thieme, Stuttgart. Widmaier, G. and Reichardt, H.D. (1973): Erfahrungen mit einer erweiterten Indikationsstellung zur ZervixCerclage in der Schwangerschaft . 261.Gyndk., 95, 16.
307-312
Comparison of two successive policies of cervical cerclage for the prevention of pre-term birth P. Lazar, B. Servent, J. Dreyfus, S. Gueguen and E. Papiernik Unit6de&&r&s de Midecine
Epiddmiologiques
de Paris&d,
et Statistiques SW I’Environnement
et la Sant6, Centre Hospitalier de Haguenau, Faculte’
France
Accepted for publication 9 March 1979 LAZAR, P., SERVENT, B., DREYFUS, J., GUEGUEN, S. and PAPIERNIK, E. (1979): Comparison of two successive policies of cervical cerclage for the prevention of pre-term birth. Europ. J. Obstet. Gynec. reprod. Biol., 9/5, 307-312. The percentage of women receiving cervical cerclage increased from 5% to 18% between two periods at Haguenau maternity hospital, according to a new policy for the prevention of pre-term birth. A parallel reduction of premature deliveries by about a half was observed in the relevant group of women. This suggests that cerclage might be employed on another basis than is currently the case, and that a randomized trial is urgently needed to define its indications more precisely. high-risk pregnancy; cervical incompetence;
cervical cerclage; prevention; prematurity _.-____-.
-.-.-___-
_____
suture (Dumont and Poizat, 1974). However, none of these proposals have involved use of the procedure in more than 2-3% of all pregnancies. Since 1971, cervical cerclage has been deliberately employed in a higher percentage of pregnancies than usual in Haguenau maternity hospital. In the period 1971-72, the rate of cerclage among women first consulting before the 29th wk of gestation was 5%, but, in 1973-74, it was increased to 18%. We have compared the rate of pre-term deliveries in these two periods and attempted to relate the difference to the different rates of cerclage. This study is of particular interest, as no controlled trials have been yet conducted to evaluate the effect of this treatment on pre-term delivery (Lancet, 1977). Obviously it cannot replace a trial, but it can show to which extent such a trial is needed and ethically justified.
Introduction
The traditional indications for a cervical cerclage to prevent pre-term delivery are either constitutional cervical incompetence of congenital or traumatic origin (diagnosed prior to pregnancy by hysterography or by clinical calibration of the cervix), or functional incompetence, usually indicated by a previous abortion late in pregnancy (Hervet and Huguier, 1961). Generally less than 1% of pregnant women have such indications. Various authors have proposed extending the use of this procedure to include women with less severe congenital and traumatic anomalies (SrketiC et al., 1975), or functional insufficiencies (Widmaier and Reichardt, 1973), or have suggested performing the intervention beyond the 16th wk of gestation up to the third trimester of pregnancy. Other authors have derived scoring systems to combine the various risk factors to assess eligibility for 307
308
P. Lazar et al.: Cervical cerclage and pre-term birth
Methods
was 5.2% in the first period and 18.3% in the second. The rate of pre-term deliveries was IS% smaller in period II, but this difference is not statistically significant. The marked difference in the rate of prematurity in the two periods among women with a cerclage is not by itself meaningful, since a higher proportion of women were operated on in period II, and women will have been included who were, on average, at lower risk of a premature delivery. The women were classified into high, intermediate and low risk groups for prematurity (as discussed above) as follows: (1) The percentage of “high-risk women” was taken as the percentage operated on in the first period (5.2%). The numbers of such women in the two periods are then 47 and 6 1, respectively. (2) The percentage of “low-risk women” was taken as the percentage not operated on in the second period (81.7%). The numbers of such women in the two periods are then 741 and 963, respectively. (3) The number of “intermediate-risk women” in each period may be obtained by subtraction and are 118 and 154, respectively. We must then select from the 859 women who did not have a cerclage in period I, the 118 who would have been expected to have had a cerclage if they had presented during period II and, symmetrically, we have to select, from the 215 women who had a cerclage in period II, the 154 who would have been expected not to have had a cerclage had they presented during period I. This was achieved thus: (a) Considering only the women presenting in period II, we constructed a discriminant equation based upon prematurity risk factors to distinguish between women who had and did not have a cerclage. (b) A score was calculated from the discriminant equation for each of the 859 women who were not
The present study includes all women having a singleton birth between February 1971 and December 1974, who had at least one examination in Haguenau maternity hospital before the 29th wk of gestation; 906 women fulfilled these criteria in the first period (1971-72) and 1178 in the second (1973-74). A birth was regarded as pre-term if delivery occurred before 37 wk of gestation. For each of these two periods we have classified the women into 3 categories: the first being those women who would have had a cerclage if they had presented in either period (“high-risk women”), the second being women who would not have been liable for cerclage had they presented in either period (‘low-risk women”), and the third being those women who would have been given a cerclage if they had presented in the second period but would not have had one if they had presented in the first period (“intermediate-risk women”). This means that, using the major change having occurred in the policy, we have been able to identify -which is unusual in such “historical” comparisons -two groups as comparable as possible between the two periods, with and without the treatment under analysis. After making this classification, prematurity rates have been compared between the two periods in the 3 categories. The classification procedure (which will be described together with the results) is based upon the statistical method of discriminant analysis (Anderson, 1958). Results
Table I shows the rates of cerclage and pre-term birth in the two study periods. The rate of cerclage
TABLE I
Description of the populations in periods I and II
Period
I II Significance NS = not signikant.
No. of cases
906 1178
% of women given sutures
5.2 18.3 P < 0.001
% of premature deliveries
8.5 7.0 NS
% of premature deliveries among women With a suture
Without a suture
23.4 10.7 P = 0.05
1.1 6.2 NS
309
P. Lazar et al.: Cervical cerclage and pre-term birth TABLE II
Predictive variables corresponding suture and scoring weights % of women with suture when the sign is present
Variable
rates
of
Scoring weight Period I
Period II
Period I
Period II
Medical history late abortion prematurity other ’
19 19 23
30 25 27
0.19 0.17 0.30
0.17 0.02 0.08
Present pregnancy open cervix short cervix
16 20
41 44
0.06 0.28
0.10 0.63
’ Primiparous aged more than 35 yr, treated sterility, uterine malformation, placenta previa.
given a cerclage in period I, and the 118 with the highest scores were designated as the “intermediaterisk” group. (c) The symmetrical procedure was applied to define the 154 “intermediate-risk” women in period II. Table II shows the variables used in the discriminant analysis and their weights within each period. Table III shows the rates of prematurity in the 6 defined groups. The prematurity rate in the second period is significantly lower within the “intermediaterisk” group of women but the differences among “high” and ‘low” risk women are not significant. These findings are consistent with a cervical cerclage protecting against premature delivery among the “intermediate-risk” group. However, the reconstituted decision rules are
TABLE III Period
Rates of prematurity in the 6 groups High-risk women
Intermediate-risk women
Low-risk women
=
#
I
g = 23.4%
118 -
II
g=
#4 = 7.1%
$& = 6.2%
Significance
NS
P = 0.01
NS
19.7%
- 19.4%
=
5.8%
obviously approximate, and it is important to consider how these might affect the conclusions. The variables used for predicting which women would have been sutured are practically the same as those which would be used to predict prematurity, and it is possible that the observed prematurity rates of 19.4% and 7.1% in the intermediate category are seriously biased (the former being too high, the later too low). An argument against this is provided by the observation of no marked difference between the corresponding rates in “high-risk” women (23.4% and 19.7%, respectively) and “low-risk” women (6.2% and 5.8%, respectively). Another argument comes from the comparison of the main risk factors of pre-term birth (previous late abortions or pre-term birth, metrorrhagia, short or open cervix in the present pregnancy) between the two periods in the intermediate group. Table IV shows that there is no major difference between the two groups, except for previous pre-term birth, which is more frequent in period I, and opening of the cervix, which is more frequent in period II. However, it is possible to take all the risk factors directly into account by calculating a risk score through a discriminant analysis, weighting the various factors predictive of pre-term birth (Papiernik and Kaminski, 1974).
TABLE IV
Main risk factors in the intermediate-risk of the two periods (%) Period I (n = 118)
Previous late abortion Previous pre-term birth First examination of the present pregnancy metrorrhagia short cervix open cervix Examination between 19 and 24 wk metrorrhagia short cervix open cervix Examination between 25 and 28 wk metrorrhagia short cervix open cervix
groups
Period II (n = 154)
3.4 17.8
2.0 2.6
7.6 5.9 0
4.5 4.5 3.0
5.1 11.9 0
5.2 12.2 2.6
3.9
4.1 21.3 9.8
15.6 0
P. Lazar et al.: Cervicalcerclage and pre-term birth
310 TABLE V
Mean values of a prematurity index (m f SE)
Period
High-risk women
Intermediate-risk
I
2.62* 0.41 41
1.51 f 0.20 118
1.03 f 0.06 741
1.18 + 0.06 906
II
2.25 f 0.25 61
1.25 f 0.15 154
1.22 f 0.05 963
1.28 f 0.05 1178
Significance
NS
NS
P = 0.02
P = 0.08
TABLE VI Period
I II Rates ratio (II/I)
Standardized rates of prematurity High-risk women
Intermediate-risk women
women
20.2% 18.1% 0.9
19.2% 1.1% 0.4
6.1% 6.1% 1.0
Low-risk
Table V gives the mean values of this index in the 6 groups. The overall difference between the two periods - the women presenting in period II being apparently at a greater risk - is significant in low-risk women only. Standardized rates of prematurity were calculated, taking the cumulated distribution of risk scores in the two periods as a standard. Table VI shows the standardized rates and their ratio. This ratio is close to 1 in the two extreme categories and much reduced (by more than a half) in the intermediate-risk category.
Discussion
The percentage of women receiving cervical cerclage increased from 5% to 18% between 197 l72 and 1973 at Haguenau hospital. When this change took place a system for scoring prematurity risk was introduced into the hospital protocols. Table II indicates how the clinical signs were taken into account before and after the change of policy. Generally, during period II, a heavier weight was given to any risk factor and, in particular, opening and shortening of the cervix were considered as major risk factors. More than 40% of women presenting with either of these signs before the 29th wk of gestation were
women
Low-risk women
Total sample
operated upon, whereas the corresponding rate was less than 20% in the first period. Very little is demonstrated of the effect of cervical cerclage in preventing premature deliveries, and no controlled trials of this procedure have been reported. Studies on women with a definite cervical incompetence have compared results of previous pregnancies of the operated women to those after treatment (Hervet and Huguier, 1961; Carollo, 1975), finding obvious and convincing differences, particularly in the reduction of late abortions. Such considerations have been used as an argument for widening the indications for such suture. Other workers (Fournil et al., 1977) have proposed reducing the proportion of women given a cerclage on the basis of a cervix calibration during the first trimester of pregnancy, but their study included no appropriate control group. The major change of policy which occurred in Haguenau hospital has allowed us to study directly the protective effect of a cervical cerclage against premature delivery by enabling us to compare two groups of women likely to be similar. As indicated in Tables III and VI, a reduction by a factor of at least 2 has been observed in the prematurity rate among women from whom a suture was performed in period II (13% of the women consulting before the 29th wk of gestation). We cannot explain this reduction by a general change in the risk factors among women presenting in the two periods, nor by an obvious bias in the definition of the groups cornpared in periods I and II. However, the increase in the frequency of sutures is not the only therapeutic difference between the two periods. In particular, the number of medical examinations also increased, as did the frequency of hospital admissions for causes other than cerclage, and the reduction in prematurity could be related to a better surveillance and treat-
311
P. Lazar et al,: Cervicalcerclage and pre-term birth TABLE VII
p-Mimetics
Not used Used
Prematurity rate in period II according to the use of p-mimetics ’ High-risk women
Intermediate-risk women
Low-risk women
10.2% 49
4.2% 119
4.6% 814
26.3% 19
42.9% 28
60.0% 10
1 Unknown for a small percentage of women.
ment during pregnancy. However, if such was the case, a general decrease in the rate of premature deliveries would have been expected, and not only in the category of “intermediate-risk” women, since the increase in examination frequency occurred among all women, even if it looks to be higher in the intermediate-risk group (Table VIII). Moreover, for the intermediate-risk women, the difference of prematurity between the two periods was not related to the number of consultations between the 29th and 37th wk of pregnancy. Anyway, it is obviously impossible to disregard completely the hypothesis that the observed difference, in the intermediate group, might be related to the special attention devoted to women with a cerclage in period II. The benefit then would be only a “side-effect” of cerclage. The greater use of /3-mimetics during period II raises a somewhat different problem, since there is no comparative point during period I when such drugs were not used. Table VII gives the available information for period II. The use of fl-mimetics was relatively rare (14% among intermediate-risk women) and was apparently of limited efficiency, since the rate of prematurity, when these drugs had to be used, was quite high: about 40% on average. However, it is obviously impossible to exclude the possibility that
TABLE VIII Percentage of hospital admissions for causes other than cerclage (29-36 gestational wk) Period
I
II Significance
High-risk women 25% 55% P < 0.001
Intermediate-risk women
Low-risk women
17% 67% P < 0.001
4% 10% P < 0.001
TABLE IX
Rate of premature deliveries in the intermediate risk category according to the prematurity risk index
Period
Value of prematurity risk index
Total
Low 1
High ’
I
13.8% 58
25.0% 60
19.4% 118
II
2.4% 82
12.5% 72
7.1% 154
0.2
0.5
0.4
Rates ratio (II/I)
i The distribution was divided at its median.
tocolytic agents contributed significantly to reducing the risk of pre-term delivery, especially in the intermediate group, either through a positive interaction with cerclage or just because, with a suture in place, the physicians used them at a higher dose or with a different pattern. In Table IX we have divided the women in the intermediate-risk group into two categories on the basis of the prematurity risk index. Cerclage looks to be of value to both those with the high- and low-risk scores within this intermediate group. Finally, our findings suggest that the increased rate of cervical cerclages in Haguenau from 1973 might have reduced the rate of premature deliveries among the new women treated by about a half, either because of the cerclage itself or due to any of the associated therapeutic attitudes. A cooperative randomized trial is then urgently needed which will enable the balance of costs and benefits of this procedure to be better assessed, as well as enabling the indications for the operation itself to be defined more precisely.
Acknowledgements
We are greatly indebted to Dr. Peter G. Smith for his help in English translation. This work was supported by grants from the Institut National de la Sante et de la Recherche Medicale, Ministere de la Sante Mutuelle GBnCrale de 1’Education Nationale and Groupe d’Etude de la PrCmaturitC et de la Souffrance Perinatale.
312 References Anderson, T.W. (1958): An Introduction to Multivariate StatisticalAnalysis, Ch. 6. Wiley, New York. Carollo, F. (1975): Closure of dilated cervix during pregnancy for prevention of premature delivery. In: Perinatal Medicine, 4th Europ. Congr..August 1974, p. 279. Editors: Z.K. Stembera, K. PolaEek and V. gabata, Georg Thieme, Stuttgart. Dumont, M. and Poizat, Cl. (1974): Etude d’un coefficient d’appreciation de la beance cervico-isthmique. A propos de 50 observations de beances trait&es par cerclage. J. Gynkc. Obste’t.Biol. reprod., 3, 981. Fournil, C., Hidden, J. and Lajoux, P. (1977): Evaluation du calibre de l’isthme u&in en debut de grossesse. Int&6t dans l’indication du cerclage du col. 134 Observations. Nouv. Presse m&d., 6, 5 23.
P. Lazar et al,: Cervicalcerclage and pre-term birth Hervet, E. and Huguier, J. (1961): B&race cervico-isthmique. Bull. F&d. Sot. Gynk. Obsttft.,13, 1-17. Lancet (1977): The Shirodkar Stitch (leading article). Lance& 1, 691. Papiernik, E. and Kaminski, M. (1974): Multifactorial study of the risk of prematurity at 32 weeks of gestation. 1. A study of the frequency of 30 predictive characteristics.J. perinat. Med., 2, 30. SrketiL, M., Salamon, B. and Peri& D. (1975): Cervical cerclage as the prevention of premature delivery. In: Perinatal Medicine, fth Europ. Congr., August” 1974, p. 281. Editors: Z.K. Stembera, K. PollEek and V. Sabata. Georg Thieme, Stuttgart. Widmaier, G. and Reichardt, H.D. (1973): Erfahrungen mit einer erweiterten Indikationsstellung zur ZervixCerclage in der Schwangerschaft . 261.Gyndk., 95, 16.
