Short Cervix
Anne Kennedy, MD
DIFFERENTIAL DIAGNOSIS
Common
Mimics
Poor Scan Technique
Nabothian Cyst
Prominent Mucus Plug
Curved Cervix
Incompetent Cervix
Multiple Gestation
Failed Cerclage
Uterine Duplication
Less Common
Loop Electrosurgical Excision Procedure (LEEP)
Trachelectomy
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Short cervix defined as length < 26 mm at 24 weeks
Increases relative risk for preterm delivery by a factor of 6.19
Sensitivity of 37% for delivery before 35 weeks, positive predictive value of 18%
Rates of preterm birth continue to rise despite extensive research
Measurement of cervical length is one method used in attempt to identify at-risk group who might benefit from intervention
However, effective interventions to prevent preterm birth remain elusive
Correct scan technique vital for accurate evaluation of cervical length
Options include transabdominal (TA), translabial (TL), & transvaginal (TV)
TA: Use amniotic fluid as acoustic window to cervix in second trimester
Transducer inferior to maternal umbilicus, angled inferiorly
Scanning in suprapubic area → shadowing by pubic symphysis
Full bladder or lower segment contraction may artificially elongate cervix → missed diagnosis of short cervix
Contraction may mimic appearance of fluid within endocervical canal
In 3rd trimester, presenting part may obscure detail: Perform TL or TV scans
TL: Used in 3rd trimester
Transducer placed at introitus
Coapted vaginal walls act as acoustic window to cervix
Safe in patients with ruptured membranes
TV: Best technique for evaluation of cervical length, dynamic changes, relationship to placenta, & to exclude vasa previa
Bladder empty
Transducer placed in vagina under direct visual monitoring
Advance until cervix in focus, retract until cervix just within focal zone
Anterior lip & posterior lip should be same thickness
Measure length along endocervical canal: Bright echogenic line
Observe for several minutes for dynamic changes ± apply fundal or suprapubic pressure
Bladder neck mucosal echo is anatomic landmark for internal os
Ruptured membranes is a relative contraindication for TV sonography
Obtain measurements
Shortest length of closed cervix on good image
Degree of dilatation of internal os
Length of funneling of membranes
Length of cervix above cerclage ± length cervix below cerclage
Recent review suggests absent cervix above cerclage is associated with preterm delivery, chorioamnionitis, & preterm premature rupture of membranes
Helpful Clues for Common Diagnoses
Mimics
Poor Scan Technique
Spurious short measurement may alter management & have patients needlessly placed on bedrest, etc.
Spurious long measurement may lead to missed opportunity to intervene in at-risk patients
Nabothian Cyst
May cause confusion with fluid in cervix
Check for normal echogenic endocervical canal “stripe”
Scan from side to side: Nabothian cysts are thin walled, should be seen separate from endocervical canal
Large nabothian cysts may distort cervix, alter contour of canal
Prominent Mucus Plug
Prominent hypoechoic material within endocervical canal
No dynamic changes
No internal os dilatation
Curved Cervix
Measure in series of straight lines & sum for total length
Incompetent Cervix
Cervix dilates without pain: Most likely to present with mid-trimester loss
Multiple Gestation
Cervical length shorter in multiples than singletons
Higher order multiples → decreasing cervical length
Recent reviews indicate that cerclage does not prevent preterm birth in multiples & may, in fact, be detrimental
Failed Cerclage
Membranes prolapse to, or through, level of cerclage
Uterine Duplication
Müllerian duct anomalies overrepresented in infertility/recurrent abortion population
In addition to variant uterine morphology, cervix may be shortened
Helpful Clues for Less Common Diagnoses
Loop Electrosurgical Excision Procedure (LEEP)
Performed for cervical intraepithelial neoplasia (CIN)
Women with a history of LEEP & cold knife conization have shorter cervical lengths than low-risk controls
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