Abstract
Background Transvaginal sonographic cervical length assessment identifies pregnant women at
risk for preterm birth, and the subsequent placement of a cervical pessary may reduce
this risk. The mechanism of action remains uncertain, and postplacement transvaginal
sonography may provide further insight into the controversial efficacy of this therapy.
Objective To identify any pre- or postplacement sonographic findings associated with preterm
delivery following cervical pessary insertion among at-risk women.
Materials and Methods This retrospective cohort study utilized electronic medical record and imaging review
of all women identified within a large tertiary care health system having undergone
cervical pessary placement for preterm birth risk reduction and subsequently delivered
between January 2013 (the adoption of this therapeutic option in our system) and March
2017. Indications for cervical pessary placement were guided by maternal–fetal medicine
consultation and required a functional cervical length measurement on transvaginal
sonography of 25 mm or less. Criteria for initial transvaginal cervical assessment
included obstetric history, multiple gestation, and current concern on transabdominal
imaging for cervical shortening. All pre- and postplacement transvaginal sonographic
measurements were determined for study purposes by re-review of each patient's images
by a single author blinded to outcome.
Results A total of 88 women were identified as having undergone cervical pessary placement
for preterm birth prevention, and 52 yielded complete delivery and imaging data for
inclusion. As expected, this was a high-risk population with 51.9% carrying multiple
gestations, 32.7% with a history of prior preterm birth, and 11.6% with a history
of cervical conization. Although previously hypothesized to represent the mechanism
of action, neither the change in uterocervical or intracervical angle was associated
with gestational age at delivery. Alternatively, preplacement imaging measurements
of cervical funneling, anterior cervical length, and cervical diameter were significantly
associated with appropriate pessary placement and decreased preterm birth. Forty-two
subjects (80.8%) demonstrated both the anterior and posterior aspects of the cervix
within the pessary (appropriate placement) and 95.2% of these subjects demonstrated
cervical funneling on initial imaging compared with 25% of those with inappropriate
placement (p = 0.002). Anterior cervical length less than 20 mm and cervical diameter less than
33 mm were associated with preterm delivery less than 28 weeks (16.7 vs. 0%, p = 0.039), and anterior cervical length less than 20 mm was associated with preterm
delivery less than 32 weeks (41.7 vs. 10.7%, p = 0.025). Cervical diameter less than 33 mm correlated with an “inappropriately placed”
pessary among 83.3% in comparison to 48.7% (p = 0.048) of women with a cervical diameter less than 33 mm. Significant associations
were noted between postplacement functional cervical length measurements and preplacement
anterior cervical length (p = 0.001) and cervical diameter (p = 0.012).
Conclusion Contrary to current thinking, no significant changes in uterocervical and intracervical
angle following cervical pessary placement were identified. However, preplacement
sonographic measurement of funneling, anterior cervical length, and cervical diameter
are predictive of appropriate pessary placement and extreme preterm birth. These may
represent markers for candidacy of cervical pessary placement. Postplacement transvaginal
sonography represents an important tool to assess potential efficacy of this therapeutic
modality, and further investigation of these factors is warranted.
Keywords
preterm birth - cervical pessary - uterocervical angle - intracervical angle - cervical
length - funneling - sonography - ultrasound
