La tunisie Medicale - 2017 ; Vol 95 ( n°03 ) : 192-195
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Résumé

Introduction : L’accouchement prématuré reste la complication majeure des grossesses gémellaires. Un col utérin raccourci entre 20 et 24 semaines d’aménorrhée est un signe prédictif d’accouchement prématuré chez les patientes asymptomatiques. Ceci dit, il n’y a pas de recommandations pour des mesures itératives du col utérin chez ces grossesses à risque.
Objectif: Evaluer les bénéfices d’un monitorage mensuel de la longueur du col utérin chez les grossesses gémellaires asymptomatiques.
Méthodes: Il s’agit d’une étude longitudinale comparant deux groupes de grossesses gémellaires (un groupe avec monitorage échographique mensuel et systématique de la longueur du col  par voie endo-vaginale et un groupe témoin) en termes de taux de dépistage de menace d’accouchement prématuré, d’âge gestationnel au moment du diagnostic, de temps gagné par la tocolyse et de terme gestationnel moyen au moment de l’accouchement.
Résultats: Quatre-vingt-neuf grossesses gémellaires ont été incluses : 35 patientes avaient un monitorage mensuel et systématique de la longueur cervicale (groupe 1) versus 64 témoins (groupe 2). Une corrélation significative a été objectivée entre une longueur cervicale mesurée entre 22 et 24 semaines d’aménorrhée inférieure à 30 mm et un accouchement prématuré avec une bonne spécificité (100%), une bonne valeur prédictive positive (100%) mais une  sensibilité de 45%. Un gain significatif a été mis en évidence dans le groupe 1 en termes de taux de dépistage de menace d’accouchement prématurée (p=0,018),de temps gagné par  la tocolyse(p=0,023), et de terme gestationnel moyen au moment de l’accouchement (p=0,046).
Conclusion : Le monitorage systématique de la longueur cervicale serait un moyen de dépistage des menaces d’accouchement prématuré chez les grossesses gémellaires asymptomatiques.

Mots Clés
Article

INTRODUCTION

The rate of multiple pregnancies is showing a significant increase in all over the world.
Preterm delivery, defined as birth before 37weeks of amenorrhea (WA), is the major cause of adverse outcomes. It is observed in approximately 54% of all twins [1].
Despite advancing knowledge of the risk factors and mechanisms associated with preterm
labor (PL) and delivery, the twin preterm birth rate has risen 36% in the United Stated during the last quarter century [2].Therefore, there is an urgent need to develop cost-effective tests for the prediction of preterm birth in twin pregnancies. Although universal screening is controversial, cervical length (CL) assessment has been useful in the management of these patients. A shortened cervix identified by transvaginal ultrasound (TVUS) at 20-24 weeks’ gestation is a good predictor of preterm birth in asymptomatic twin pregnancies [2-4]. However, there are no recommendations about serial CL measurements.
The objective of this study was to evaluate the benefits from monthly CL monitoring in
asymptomatic twin pregnancies in terms of PL screening, time saved by tocolysis and medium gestational age (GA) at birth.

METHODS
This was a prospective and comparative study conducted over a period of 15 months.  We
selected all multiple pregnancies managed in our obstetrics and gynecology unit.
Gestational age was based on the known last menstrual period and confirmed by first trimester ultrasound, or based on first trimester ultrasound in all patients.
Patients were enrolled in two groups: 
- In the first group (G1), we included patients managed in our department right from the first trimester with a monthly and systematic TVUS measurement of the CL. Initial CL
measurement started between 22 and 24 WA, followed by serial CL measurements each
month. All CL measurements were measured by 4 – 8 MHz transvaginal probes (ULTRASONIX, SONIX OP) with an empty bladder with the optimal image [5].The shortest
functional CL recorded was used as this has been found to be the most reproductive
measurement [6].
- In the second group (G2), we included patients managed initially in other clinics with no
monitoring of CL and who were transferred to deliver in our department during the same
study period.
We compared the two groups of patients in terms of: PL screening rate, GA at the diagnosis of PL, time saved by tocolysis and GA at delivery.
Fisher exact test, Student t test, and multivariable analysis were used when appropriate (SPSS for Windows 16.0; SPSS Inc, Chicago, IL).

RESULTS
During the study period, 99 patients with twin pregnancies were supported in our unit: 35 patients were managed starting from the first trimester and were included in the first group. These patients had systematic monthly CL measurements. 64 women with twins had a traditional prenatal care or only had given birth in our department. These patients were included in the second group.
The mean age was significantly higher in the first group of patients. The main epidemiological characteristics of the two groups of patients are detailed in table 1.
Of a total of 35 patients in G1, CL was inferior to 30 mm in 9 patients.
The terms of delivery according to the CL measured between 22 and 24 WA are detailed in Table 2.
Thus, There was a significant relationship between CL measured between 22 and 24
WA inferior to 30 mm and PL (p = 0.02). Similarly, we have found a high specificity (100%)
and a high positive predictive value (PPV) (100%)of a CL inferior to 30 mm at 22 WA in the
screening for PL. The sensitivity remains average: 45%.
In addition, the systematic and monthly monitoring of CL routinely performed in G1 had
highlighted the following results:
- 11 patients had presented cervical changes before 34 WA. Among these patients, 6 (54.5%) had no uterine contractions. In G2, this screening was possible in only one patient (1/14) and the difference was significant between the two groups (p = 0.018).
- The medium GA at delivery was 34.7 [31.8-38.5] WA in G1 versus  29 [27.8-38] WA  in
G2. This difference was significant (p = 0.046).
- The rate of premature birth was 63.6% in G1 versus 57.14% in G2 (p=0.625).
- The time saved by tocolysis was significantly different between the two groups, 5.5 WA
in G1 against 2 WA in G2 (p = 0.023).
-36.3% of newborns were admitted to neonatal unit in G1 versus 50% in G2 (p=0.407).
Thus, we can conclude that there was a benefit from PL screening using systematic ultrasound CL measurement in terms of medium GA at delivery, and time saved by tocolysis. These results are summarized in table 3.

DISCUSSION
In our study, we have demonstrated the importance of ultrasound in assessing the risk of
preterm delivery, main complication of twin pregnancies. Indeed, we found a
significant relationship between CL  measured between 22 and 24 WA  inferior to 30 mm and
premature delivery with p = 0.02.
Similarly, a significant benefit was demonstrated through this systematic CL
measurement in: screening for PL (p=0.018), time saved by tocolysis (p=0.023),
as well as medium GA at birth (p=0.046).
Although these significant results, one limitation should be mentioned which is the small number of patients. Thus, we must work to generalize this ultrasound management of twin pregnancies to all obstetrics units in our country.
Another limitation of our study lies in the application of these results into clinical practice
with the well-known fact that the prediction of preterm birth does not necessarily lead to the
prevention of preterm birth. Indeed, efforts to prevent preterm birth in twins have generally
not been supported by prospective, randomized trials [5,7].
Although universal screening is controversial, CL assessment has been useful in the
management of patients with preexisting risk factors for preterm delivery. Given that over half of all twins are delivered prior to term, an awareness of CL tends to impact patient counseling  and the management of twin pregnancies [8].Moreover, it has been shown that in twin pregnancies, only the obstetric history (history of premature labor) and ultrasonographic CL measurement are predictive of preterm delivery [9].
Despite the sometimes conflicting results in the literature, the CL measurement still of a great contribution in the management of patients with risk factors for preterm birth [10]. Among the various ultrasound measurements techniques, transvaginal measurements give the best results [11-13].
Similarly, all studies found a significant association between the CL decrease at 20-24 WA in twin pregnancies and preterm delivery [14, 15]. In a prospective study of 1163 twin
pregnancies, To et al. [16] demonstrate that transvaginal ultrasound CL measurement between 22 and 24 WA is more relevant than the obstetric history to identify patients at risk of preterm delivery before 32 WA with a specificity of around 89%.
It is held that a CL measured at the second trimester lower than 20-25mm increases the risk of preterm delivery 3 to 5 times[10].  In a study of 251 women with twin pregnancy, Vayssière et al.[17] demonstrate that a CL measured between 21 and 23 WA less than 25mm predicts preterm delivery before 32 weeks with a sensitivity of 38%, a specificity of 97% and a PPV of 38%. In our study, the threshold used was 30mm, and we have demonstrated a significant relation between a CL less than 30 mm and PL (p=0.02) with a high specificity (100%),and a high PPV (100%). The sensibility was 45%.
Recently, Foxet al. illustrate via a study of 121 twin pregnancies [18], that changes of more
than 20% in CL between 2 measurements performed during the end of the second trimester are an important predictor of preterm birth; even if CL measured remains above 25mm. 
This ultrasound monitoring of the CL, although the threshold for identifying women at risk of
preterm delivery is variable from one study to another, and from one team to another, remains paramount in the management of twin pregnancies and in the prevention of preterm delivery .
CONCLUSION
Serial CL measurements are a significant predictor of early preterm birth in asymptomatic
twin pregnancies although the threshold for identifying women at risk is variable from one
team to another.

TABLES:

Table1: Main epidemiological characteristics of the two groups of patients.

Table 2:
Mean gestational age at delivery in patients of group 1 according to the cervical length measured between 22 and 24 weeks of amenorrhea.

Table 2: Mean gestational age at delivery in patients of group 1 according to the cervical length measured between 22 and 24 weeks of amenorrhea.

Table 3:Comparison of pregnancies outcomes between the two groups of patients.

 

 

 

Références
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