As pointed out in our previous posts on this subject, one of the greatest frustrations of cervical incompetence has been to establish its diagnosis in a timely and reliable fashion. Since multiple factors can contribute to cervical incompetence, and the patient’s own response may not be consistent during different pregnancies, cervical incompetence must not be viewed as a ‘disease’, so much as a ‘syndrome’ with a common final pathway. And, being a ‘syndrome’ in this case makes it easier to understand why there is not a ‘diagnostic test’ for cervical incompetence – indeed all we really have are several different methods of screening for the condition.
I divide screening into several different categories. The first is the patient’s obstetrical history – the classic approach upon which we relied during my training. If the patient presents for consultation with a history of premature delivery or midtrimester pregnancy loss, it is important to characterize the events surrounding the delivery in as much detail as possible from both the patient’s recollections and the medical records. For example, some of the questions asked include: gestational age at delivery; presence or absence of painful contractions prior to presentation and the duration of the same; cervical status at presentation (long, short, firm, soft, degree of effacement); amount of amniotic fluid (too little, too much); condition of the membranes (intact, ruptured, or ballooning in the vagina); evidence of prior or concurrent urinary tract infection, sexually transmitted infection or bacterial vaginosis; other pregnancy-related or previous medical conditions (including history of infertility and known Mullerian anomalies) and type of medical therapy; size of the baby and appropriateness for gestational age; course of the labor itself (short, long, use of oxytocin and why); outcome of the baby and neonatal complications if the baby was not stillborn; pathologic evaluation of the placenta and baby; laboratory studies obtained at the time of admission (e.g., CBC, urinalysis and culture); and, if this was not a first pregnancy, comparison of this pregnancy to the others with regard to these factors and intervening procedures (e.g., traumatic vaginal delivery, D&C, cervical conization, myomectomy). The goal of this line of questioning is to try to separate the possible diagnosis of cervical incompetence from other causes that may or may not put another pregnancy at risk for premature delivery. The patient with cervical incompetence is much more likely to have a history of relatively painless labor, presenting with advanced cervical dilation and effacement (out of proportion to the labor), followed by a rapid delivery. If she has had previous pregnancies, there is also a tendency for sequentially earlier deliveries with cervical incompetence.
The problem with the ‘historical approach’ to screening is that it often meant a patient lost one or more pregnancies before a ‘diagnosis’ of cervical incompetence was established and if the pertinent historical information could not be accurately obtained, the diagnosis might be further delayed. To address that concern, over the years, I have put together my own little laundry list, based on both experience and, where available, the scientific literature, of women who should be observed more carefully, even during a first pregnancy, for evidence of cervical incompetence. Included among those risk factors are those mentioned in our last post: family history of premature delivery and cervical incompetence; maternal obesity; congenital uterine abnormalities; uterine fibroids; previous uterine surgery (e.g., D&C, removal of uterine septum, myomectomy); previous cervical surgery; history of maternal infertility and assisted reproductive techniques for conception; multiple gestation; recurrent vaginal and urinary tract infections; connective tissue disorders (e.g., Ehlers-Danlos syndrome and Marfan’s syndrome) and perhaps collagen vascular diseases; polycystic ovary syndrome/insulin resistance; and perhaps diabetes. In addition to predisposing risk factors, one should remain alert to those that develop during pregnancy and also maintain a high index of suspicion related to certain patient complaints such as increasing pelvic pressure or excessive vaginal discharge, both of which may accompany premature cervical effacement.
The major contributor today to cervical evaluation in both categories above, and the primary means of detecting cervical incompetence in the presence of new ‘signs and symptoms’ or, fortuitously, during other assessment, has been ultrasound. I am not going to make any effort to review the literature that debates the value of ultrasound in this regard. In the most general sense, cervical length in midtrimester is inversely proportion to the risk for preterm delivery; and in women at greatest risk for preterm delivery, the course of their cervical changes and the events surrounding delivery often are consistent with the traditional history we attribute to cervical incompetence.
However, evaluation of the cervix involves more than simply measuring the length (or what’s left of the length) of the endocervical canal. Other factors to consider are the changes in length over time, the configuration of the internal os and the endocervical canal, and the presence of and degree of distention by membranes in the endocervical canal. In the patient who is being followed for possible cervical incompetence by history, or who has risk factors for the same, serial evaluation may be necessary and, in my practice, preferable. Most women with cervical incompetence will develop visible changes in the configuration and length of the endocervical canal between 16 and 24 weeks. And, with serial follow-up, one is more likely to detect changes at a time when intervention can still provide a favorable outcome for the pregnancy.
One of the questions that has been raised is whether or not ALL pregnant women should be routinely assessed for cervical incompetence in midtrimester. I can tell you that over the past 6 years in my own experience, at least one-third of the cases of cervical incompetence necessitating placement of ‘rescue’ cerclages have been in women between 18-24 weeks with no previously recognized risk factors in whom advanced cervical changes were detected during the course of a routine sonogram to assess fetal growth and anatomy usually scheduled for that time in pregnancy.
In most cases, a ‘suspicious’ cervix was first noted during transabdominal assessment and then confirmed transvaginally. When one considers the safety of ultrasound and the speed with which a transvaginal sonogram can be performed, the epidemic of obesity (a risk factor itself) that precludes adequate transabdominal assessment of the cervix, and the potential savings to the healthcare system by preventing the delivery of even a few 23-26 week babies annually at any institution, I think the cost of including cervical assessment during the routine pregnancy ultrasound examination that has become standard at 18-22 weeks, the additional cost of the transvaginal ultrasound could be readily justified…