Diagnostic ultrasound ( PDFDrive )

CHAPTER 44 Cervical Ultrasound and Preterm Birth 1503
H
A
B
FIG. 44.13 Dynamic Dilation of the Cervix, Transvaginal Ultrasound. (A) Initially, the internal os appears closed (arrowhead). (B) Image
obtained 30 seconds later shows funneling of the internal os (arrowheads). The residual closed cervix (calipers) measures 12 mm. H, Fetal head.
asymptomatic high-risk women during serial evaluations signiicantly
improved the prediction of PTB. Patients with uterine
contractions also had a greater incidence of dynamic cervical
change than asymptomatic patients. 51 In both clinical scenarios,
the minimal closed cervical length, not the “dynamic change,”
was the better predictor of SPTB. Several noninvasive stress
techniques have been suggested to elicit cervical change and
improve the ability of TVS to predict cervical incompetence.
hese stressors include transfundal pressure (pressure applied
at the fundus for 15 seconds that elicits >5 mm in cervical length
shortening), standing, and coughing. Several small studies found
that transfundal pressure was the most efective tool in cervical
assessment and the most sensitive tool to predict progressive
cervical shortening. 52,53
Other Sonographic Features
Several sonographic features other than cervical length have been
studied to predict SPTB, including canal dilation, absence of the
glandular area along the length of the canal, and amniotic luid
debris. Each feature is associated with an increased risk of PTB
independent of cervical length. Cervical canal dilation of 2 to
4 mm was associated with a 5.5-fold increased risk of SPTB. 54
he cervical glandular area is a hypoechoic zone that runs along
the length of the cervical canal (see Fig. 44.4B). In 388 unselected
women, an absent cervical glandular area at 21 to 24 weeks’
gestation predicted SPTB before 35 weeks (odds ratio of 129),
suggesting a strong association. 55
Cervix: Abnormal Findings on TVS a
Shortest closed cervical length <25 mm
Presence of funneling
Presence of positive response to fundal pressure
Presence of amniotic luid debris (“sludge”)
Shortening of 8-10 mm since previous TVS
a Gestational age less than 30 weeks.
“Sludge” or debris can be observed at ultrasound examination
as free-loating echogenic material in close proximity to the cervix
(Fig. 44.14, Videos 44.2 and 44.3). Samples of the sludge in patients
with impending preterm delivery have been aspirated under
ultrasound guidance, and the microbiologic examination reveals
clusters of inlammatory cells and bacteria. Presence of sludge
is an independent risk factor for SPTB, 56 PPROM, increased
concentration of microbes within the amniotic luid, and histologic
chorioamnionitis in asymptomatic patients at high risk for
spontaneous preterm delivery. Furthermore, the combination
of “sludge” and a short cervix conferred a greater risk for SPTB
than a short cervix alone. 57
CERVICAL ASSESSMENT IN SPECIFIC
CLINICAL SCENARIOS
Asymptomatic Patients
General Obstetric Population Screening
he prevention of PTB is a major health care priority. Only about
10% of spontaneous early PTBs occur in women with a prior
history. 58 his leaves approximately 90% of PTBs occurring in
women with no prior history of PTB, that is, the “low-risk”
population.
It has been shown that over 95% of women without a prior
PTB and with a singleton gestation have additional risk factors
that would place them at increased risk for PTB, regardless of
cervical length. 59 herefore perhaps the term “low risk” needs
to be redeined. Two large randomized clinical trials have
demonstrated that in women with no prior history of PTB, a
combined approach in which mid-trimester TVS screening for
cervical length is used to identify patients at risk for preterm
delivery (cervical length of <20 mm), followed by the administration
of vaginal progesterone gel from the mid-trimester pregnancy
until term reduces the rate of PTB before 33 weeks of gestation
up to 45%. 60,61