Approach Considerations

The diagnosis of cervical insufficiency is either based on a history of midtrimester pregnancy loss or a combination of clinical presentation, physical examination, and sonographic measurement of cervical length.

Ultrasonography

Sonographic measurement of cervical length, ideally via transvaginal ultrasonography, is useful in the evaluation of these patients. A short cervical length, which is typically defined as less than 25 mm, has been consistently associated with an increased risk for preterm birth, regardless of other risk factors.^{[2, 3]}Cervical effacement appears to begin at the internal os and proceed caudally, with the appearance of a funnel-shaped opening at the internal os ("funneling"), which results in progressive shortening of the cervical canal.^[30]However, the presence of funneling does not add appreciably to prediction of the risk for preterm delivery with a short cervical length.^[31]

In asymptomatic women with a prior preterm birth, serial transvaginal cervical length screening is typically performed starting at 16 weeks’ gestation and is repeated every 2 weeks until 26-28 weeks’ gestation. For women without a history of preterm delivery, the American College of Obstetricians and Gynecologists (ACOG) recommends transabdominal cervical length assessment at the time of the fetal anatomical survey (between 18 and 22 weeks’ gestation), followed by transvaginal measurement if a short cervical length is suspected.^[32]Although a 2013 Cochrane review did not find sufficient evidence to recommend routine cervical length screening for all pregnant women, the ACOG acknowledges that this screening strategy may be considered.^{[32, 33]}

Symptomatic women who present with threatened preterm labor may be evaluated with cervical length measurement in an attempt to predict the likelihood of preterm birth. Even in the presence of uterine contractions, preterm birth is unlikely to occur with a cervical length of greater than 30 mm.^{[34, 35]}Conversely, a cervical length of less than 15 mm in symptomatic women has been shown to predict approximately 60% of the women who will ultimately deliver within 7 days of presentation.^[36]When considering women with an intermediate cervical length (between 15 and 30 mm), combining cervical length assessment with fetal fibronectin testing may be particularly useful.^{[4, 5]}

Fetal Fibronectin Testing

Fetal fibronectin (fFN) is a large fetal glycoprotein that promotes cellular adhesion at uterine-placental and decidual-fetal membrane interfaces and is released into cervicovaginal secretions when this extracellular matrix is disrupted, leading to its use as a predictor of preterm delivery.^[37]Its use is limited to women with a gestational age between 22 and 34 weeks, as long as fetal membranes are intact and cervical dilatation is less than 3 cm. Sample collection is performed by placing a swab in the posterior vaginal fornix, which should be performed prior to digital or ultrasound examination of the cervix.^[38]Several studies have demonstrated the utility of fFN testing, in addition to cervical length assessment, with a significant improvement in the prediction of preterm delivery in women with a positive fFN and a cervical length less than 30 mm.^{[4, 5]}

Treatment & Management

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