© Springer-Verlag London 2015
Grigoris F. Grimbizis, Rudi Campo, Basil C. Tarlatzis and Stephan Gordts (eds.)Female Genital Tract Congenital Malformations10.1007/978-1-4471-5146-3_1515. Cervical Weakness in Women Who Have Uterine Anomalies: Impact on Pregnancy Outcome
(1)
Obstetrics and Gynaecology, Liverpool Women’s Hospital, Crown Street, Liverpool, L8 7SS, UK
(2)
Department of Gynaecology, Miscarriage Clinic, Liverpool Women’s Hospital, Crown Street, Liverpool, L87SS, UK
Keywords
Cervical weaknessUterine anomalyTransvaginal cerclageTransabdominal cerclageOverview of Uterine Anomalies
Uterine anomalies may be broadly grouped into congenital uterine anomalies (CUA) or acquired anomalies (such as leiomyomas, adhesions or polyps). Congenital uterine anomalies arise from aberrations or malformations of the female genital tract. The normal development of the reproductive tract is characterised by complex processes of differentiation, migration, fusion and subsequent canalization of the Mullerian system [1]. A spectrum of CUA ensues depending on when and how the embryological development of the Mullerian and paramesonephric ducts are affected.
The prevalence of CUA has been variably reported to be between 1 and 10 % [2]. The true population prevalence is difficult to assess because there is no universally agreed standardised classification system. We endorse the European Society of Human Reproduction (ESHRE)/European Society of Gynecological Endoscopy (ESGE) classification system of female genital anomalies that arose pursuant to a working group named CONUTA (CONgenital Uterine Anomalies) as this represents the most updated and clinically orientated version [3]. The detailed classification is discussed elsewhere in this book. Briefly, the main classes and subclasses are as follows: normal uterus, dysmorphic uterus, septate uterus (partial and complete), bicorporeal uterus, hemi-uterus, aplastic uterus and unclassified [3].
The modalities used to diagnose CUA typically include ultrasound, hysterosalpingography (HSG) or under direct vision with hysteroscopy. Laparoscopy and magnetic resonance imaging (MRI) may also be performed. Three- dimensional (3-D) and four- dimensional (4-D) ultrasound have the advantage of being non invasive and allow complete assessment of uterine morphology. In several studies, 3-D ultrasound has been favourably compared to HSG and laparoscopy in the diagnoses of CUA [4, 5].
Cervical Weakness and CUA
Cervical weakness (expressed hitherto in the literature as cervical incompetence) is a notoriously difficult entity to diagnose with certainty. The Euro-Team Early pregnancy protocol stated that there is no agreed definition of cervical weakness by absolute measurable or reproducible criteria [6]. Some define cervical weakness as the “history of painless dilatation of the cervix” resulting in second or early third trimester delivery coupled with the passage without resistance, of a size 9 mm Hegar dilator [6]. Other definitions include: a physical defect in the strength of the cervical tissue that is congenital or acquired [7] or recurrent second trimester or early third trimester loss of pregnancy caused by the inability of the uterine cervix to retain a pregnancy to term [8].
Since the most prominent clinical manifestations of cervical weakness are a history of spontaneous second trimester loss or preterm labour we focus on these in association with CUA. The possible hypothesis linking mid-trimester and preterm labour to CUA is that they may be an associated functional or anatomical weakening of the cervix.
Impact on Pregnancy Outcome
Although some CUA may have no impact on pregnancy outcome, others may contribute to miscarriage, intrauterine growth restriction and preterm labour [9, 10].
A recent review of CUA in a high-risk population, including miscarriage suggested a prevalence of 13.3 % [11]. In the recurrent miscarriage population, the prevalence of reported uterine malformations range widely from 1.8 to 37.6 % [12]. The septate uterus is the commonest congenital structural abnormality. A review of 24 studies suggested that the prevalence of CUA in the RM population is as high as 16.7 % compared to 6.7 % in the general population [13]. There are an abundance of studies describing CUA and miscarriage rates however few differentiate between early pregnancy or first trimester losses and mid-trimester loss (MTL) (between 12 and 24 weeks).
Mid-trimester Losses
Spontaneous mid-trimester losses may arise from cervical weakness alone or cervical weakness that is precipitated by the presence of a congenital uterine anomaly. A recent case-control study suggested a threefold increased risk of a MTL with a diagnosed septate or bicornuate uterus [13]. In a systematic review, the association between arcuate uteri and normally shaped uteri in terms of the risk of mid-trimester losses was analysed. Pooled analysis of four studies [14–17] revealed a significant increase in MTL in the women with arcuate uteri compared to women with a normal uterus (RR 2.39; 95 % CI .133–4.27; p = 0.003). Other studies [15, 18] also demonstrated a doubling in the risk of MTL in association with a bicornuate uterus. The risk of MTL was described as being almost 10 % in another study evaluating women with a unicornuate uterus [19].
Preterm Delivery
A similar continuum of cervical weakness that causes spontaneous mid-trimester losses may lead to preterm delivery. A preterm delivery rate of 20 % was quoted in a study of 290 women with a unicornuate uterus [19], while in a smaller study; the preterm delivery rate was quoted as high as 66 % [20]. Another cohort study also concluded that women with any type of CUA had a higher chance of preterm delivery [21].
A systematic analysis of seven studies [2] demonstrated that the presence of an arcuate shaped uterus was not a risk factor for preterm delivery. However the limitation in this pooled analysis was a high degree of heterogeneity amongst the different studies. Five of these studies revealed a significant increase in preterm delivery (RR 2.14; 95 % CI 1.48–3.11; p < 0.001) in women with canalization defects, particularly in women with subseptate and septate uteri [2]. There was also a significant association between increased preterm delivery and women with unification defects (RR 2.97; 95 % CI 2.08–4.23; p < 0.001).
A more recent cohort study of 158 patients describe an increased risk of preterm birth in women with arcuate, septate and T-shaped uteri, and an even higher risk in women with unicornuate, bicornuate and didelphic uteri [22].
Management of Cervical Weakness and CUA
Opinions are divided regarding the role of hysteroscopic surgical uterine correction (metroplasty) in the presence of septate or subseptate uteri. While there are a number of uncontrolled small studies claiming improvements in future pregnancies following resection [23, 24], there are no randomised controlled trials to support these observations. A recent meta-analysis of the virtues of metroplasty to improve reproductive outcomes in patients with septate uterus found an overall favourable outcome [25]. Outcomes from the on-going TRUST trial (The Randomised Uterine Septum Transection Trial) comparing hysteroscopic metroplasty and expectant management in a miscarriage population are eagerly awaited [26].
Cervical Length Measurements
Ultrasound assessment of cervical length to detect cervical weakness has emerged as an effective prognosticator for preterm birth especially in women with a previous history [27]. Serial transvaginal cervical length measurements (CLM) are far superior and more reliable than digital cervical examination in assessing the length of the cervical canal, having an inter- observer and intra- observer variability of less than 10 % [28].
The risk of adverse obstetric outcome is inversely related to the length of the cervix and the gestational age at detection of a short cervix. Cervical length of less than 25 mm has been found in most populations to have the best predictive accuracy for preterm birth and mid-trimester loss and may be the most reliable threshold to define a high-risk population [29, 30].
A large randomised study of 47,000 low risk women was conducted where women were screened for cervical shortening at 23 weeks gestation [31]. The cervical length was measured at 15 mm or less in 470 women who were consequently randomised to cerclage or expectant management. The incidence of preterm delivery was similar in both groups; therefore the insertion of an ultrasound indicated cerclage was not deemed beneficial in women who have an incidental finding of a short cervix, in the absence of a previous mid-trimester loss or preterm birth [32]. Conversely women with prior obstetric risk may benefit from an ultrasound finding of a short cervix. A meta- analysis of four randomised controlled trials demonstrated that those women with a previous mid-trimester loss or preterm birth and a cervix of <25 mm had a better success rate of pregnancies continuing into the third trimester following insertion of cerclage [33].
Transvaginal Cervical Cerclage
The role and rationale for cerclage is an attempt to strengthen the internal cervical os to maintain a pregnancy. In the twentieth century, Shirodkar [34] and McDonald [35] described the two classical techniques of transvaginal cervical cerclage (TVC). The difference in technique is that with a Shirodkar cerclage, the bladder is reflected to enable the suture to be placed as close to the internal cervical os as possible per vaginum. The choice of technique is usually at the discretion of the surgeon. Evidence suggests that there is no significant difference in the preterm delivery rate when both the Shirodkar and McDonald technique are compared [36]. Cerclage is a common prophylactic intervention for mid-trimester loss and preterm delivery despite the lack of a well-defined population for whom there is clear beneficial evidence. Transvaginal cerclage is not without risks. The procedure is associated with an increased likelihood of medical intervention, hospital admission, puerperal pyrexia, induction of labour and caesarean section.
The largest study to evaluate the efficacy of transvaginal cerclage included 1,292 women at risk of preterm delivery [37]. The authors concluded that women with a history of at least three previous MTL’s were the only group to derive a benefit from cerclage placement. The overall risk of preterm delivery reduced from 32 to 15 %. Similar results were found in a multi-centre randomised controlled trial however the criteria for patient selection consisted of patients found to have a short cervix on routine transvaginal scanning at 22 weeks. Those women with a cervical length of 15 mm or below were randomised to cerclage or expectant management. The preterm delivery rate prior to 33 weeks was 22 % in the cerclage group compared to 26 % in the control group [38].
The CIPRACT trial recruited 35 women with a history suggestive of cervical weakness and CLM <25 mm before 27 weeks gestation. Preterm delivery prior to 34 weeks was 0 % when treated with cerclage compared to 44 % in the control group. The authors concluded that therapeutic transvaginal cerclage with bed rest reduces preterm delivery [8]. A further randomised controlled trial failed to demonstrate an improved perinatal outcome with transvaginal cerclage proposing ultrasonographic dilatation of the internal os and shortening of the distal cervix is a consequence of pathophysiological processes such as inflammatory and infective stimuli [7].
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