The Cervix

Cervix

• can be assessed clinically w/ a digital exam for dilation, position, consistency, and length

  • is subjective

• Transabdominal or transperineal approach can be used

What type of U/S is best able to accurately determine cervical length?

Transvaginal

Transvaginal Cervical U/S

• have pt empty bladder

• lithotomy position

• insert trdx or have pt insert

• align trdx w/ endometrial stripe in longitudinal plane

• obtain a sagittal view of the cervix, w/ the long axis view of echogenic endocervical musoca along the length of the canal

• lengthen out the cervix and measure from internal os to external os

• observe cervix for dynamic changes

• fundal pressure?

Incompetent Cervix

• premature opening or shortening of the cervix that may lead to fetal loss

• may “funnel” (dilation of the internal os)

  • sign of cervical incompetence

  • dilation of the internal part of the cervical canal and reduction of the cervical length

  • >50% funneling before 25 weeks is associated w/ approx. 80% risk of preterm delivery

    • measure:

      • % funneling → funnel length(functional cervical length + funnel length)

      • depth and width of funnel length

    • shape:

      • U or V shaped funneling

What changes might we see w/ an Incompetent Cervix?

• changes in length and degree of funneling over the course of the ultrasound exam

• cervical changes occur in the absence of uterine contractions

Incompetent Cervix

• cervix may open and allow fetus to pass into vaginal canal → Bulging Bag (BBM)

• Hour-glassing

• If enough cervix remains, a cerclage may be put in place to “stitch” the cervix closed in effort to prevent Preterm delivery (PTD)

  • would not place cerclage in the presence of major fetal anomaly, PROM, infection or placental abruption

Cerclage U/S:

• confirm that the cerclage is intact by visualizing both sides of the string on either side of the cervical canal

• measure cervical length

• note any funneling and measure the funnel width and length

PROM (Premature Rupture of Membranes)

• prior to term (37 weeks)

• once the membranes rupture, delivery is recommended when the risk of ascending infection outweighs the risk of prematurity

PROM Risk Factors:

• PROM in a prior pregnancy

• Illicit drugs (cocaine)

• Anemia

• Low body mass index (BMI <19.8 kg/m²)

• Nutritional deficiencies (copper + ascorbic acid)

• Uterine Overdistension (polyhydramnios, mutliples)

• Intra-amniotic infection (chorioamnionitis)

• Invasive procedure (Amniocentesis, CVS, fetoscopy, cerclage placement)

PROM is predominantly a clinical diagnosis:

• watery vaginal discharge

• visual pooling of clear fluid in the posterior fornix of the vagina or leakage of fluid from the cervical area

• an alkaline pH of th cervicovagial discharge, which is tyically demonstrated by seeing whether the discharge turns yellow nitrazine paper to blue (nitrazine test)

• microscopic ferning of the cervicovaginal discharge on drying

• evidence of diminished amniotic fluid

PROM U/S findings:

• oligohydramnios

• anhydramnios

Preterm Labor (PTL)

• preterm birth is the leading cause of perinatal mortality and morbidity

• maternal risk scoring fails to detect up to 70% of infants who are delivered spontaneously before term

PTL risk factors:

• previous PTL

• cervical incompetence

• smoking

• nonmedical drug use

• multiple GA

• polyhydramnios

• vaginal bleeding

• uterine anomalies

• excessive uterine contractions

PTL Detection

• cervical changes

• fetal fibronectin

• is there PROM?

PTL Treatment

• corticosteroids for baby’s lung development

• best rest if mild

• pregesterone gel or tablets

• cerclage

• antibiotics may be given if bacteria is suspected as a cause of PTL

• Tocolytic Meds ( to attempt to stop contractions)

Tocolytic Meds

• often only work for a short period of time

• Indomethacin - can cause premature closure of DA w/ prolonged use

• Magnesium sulfate can cause the pt to be lethargic, dizzy, and weak

• many others meds may be used

Fetal Fibronectin (Ffn)

• fFN is produced by decidual cells and is a glycoprotein

  • “Glue” in utero-placental junction

  • Normally absent from vaginal secretions from 24-36 weeks

• an fFN test is a safe, reliable, non-invasive test to tell if the cervix may be getting ready for delivery

• not useful for predicting labor in women at risk for preterm labor

The fFN test should only be used for those who:

• have intact amniotic membranes

• have a cervix that has not dilated >3cm

• have only slight vaginal bleeding

• do not have cervical cerclage

Negative fFN test result:

• very accurate

• shows that labor has not started and is unlikely to occur within the next 14 days

Positive fFN test result:

• may show that labor has started

• but false-positives are common

False-positive fFN test result:

• can occur if a woman has recently had:

  • a pelvic exam

    • to reduce risk of a false positive, it’s important that a fFN test be done after a manual pelvic exam

  • sexual intercourse

  • uterine contractions

  • vaginal bleeding