Cervical Ultrasound and Preterm Birth (Lecture 16)

TRUE or FALSE: The cervix has more muscle tissue than fibrous tissue.

FALSE: The cervix has more FIBROUS tissue.

What is the function of cervical mucous?

Seals uterus during pregnancy (mucus plug) and prevents upward bacterial migration into the uterus

Name 2 pitfalls of TAS of the cx.

- Overdistended bladder can artificially elongate the cx length by compressing it

- Empty bladder

- Low amniotic fluid

- Low fetal head (cranium shadows over cx)

- Uterine contractions may falsely elongate cx (wait for 15 mins)

What U/S method is the gold standard for measuring the cx?

Transvaginal ultrasound

What are the 2 pitfalls of measuring the cx using TVS?

- Excess pressure elongates cx (see if ant and post lips have equal thickness)

- Dynamic cx: responds to pressure changes on cx (applying manual pressure to uterine fundus for 15 secs then let go, evaluate uterus for 5 mins to see any changes in length of cx)

What is the normal length of the cervix?

2.5-4 cm.

Name 1 complication of using a TVS probe.

- Stimulate premature contractions

- Risk of infections w/ PROM (premature rupture of membranes)

- Inc risk of bleeding w/ placenta previa

What is cervical effacement? When does it occur? What happens to the cervix?

TAt 30 wk GA, thinning and softening of cervix occurs before labor, which shortens the cx

A patient who is 24 wk GA comes in with a 1.5cm cx. Is this considered normal? If not, what is there an increased risk of?

This is NOT considered normal. The cervix should be 2.5-4cm before 30 wk GA. Since her cervix is shortened, there is an increased chance of preterm birth.

What is cervical insufficiency? What is the CP?

- Inability to support full-term pregnancy due to functional/mechanical defect of cx

- CP: acute painless dilation of cx usually in mid-trim

What are the pros of using a translabial/perineal probe when TV is not an option?

- Dec. risk of infection

- No disturbance of inner anatomy

What are mechanical failures associated with cervical insufficiency? Name 2 specific examples.

Cervix fails to remain closed under pressure

Examples of causes:

- Defect in structural integrity of cx

- Previous injury to cx (biopsy, D&C)

- DES/T-shaped uterus

- Congenital anomalies (septum)

What are functional failures associated with cervical insufficiency?

Premature cervical ripening (dilation and effacement too early) due to infections or hormones.

What is preterm birth?

Delivery before 37 weeks GA

At what week GA must the fetus be to have a chance of survival at birth?

24 wk GA

(However, want fetus at saccular stage (32 wks) for better lung development)

What is premature shortening of the cx?

Before 30 wks, if cx measures less than 2.5cm on TVS (& less than 3 cm on TA)

What is funneling of internal os? What are abn widths and lengths of the funnel?

- Dilation and herniation of membranes into cervical canal

- Width of the funnel - more than 8mm (TAS) or 5mm (TVS) = abn

- Length from top to bottom of funnel = more than 3-6 mm = abn

What is a T-shape funnel?

Normal (no funelling)

Which funnel shape has the worst prognosis?

a) Y shape

b) U shape

c) T shape

d) V shape

b) U shape

- Since the anterior and posterior lips of the cx are pushed out of the way, there is a greater chance that fetal parts can be seen in the tunnel

What gives the appearance of a fake hourglass shape?

Uterine contractions

(reevaluate in 10-15 mins)

What is fetal fibronectin (FFN)?

Glycoprotein released into cervicovaginal fluid in response to inflammation/separation amnoichorion from decidua. Binds the amniochorion to decidua

What treatment options are available to patients experiencing preterm birth?

- Vaginal progesterone

- OHPC progesterone = synthetic and mc used w/ high risk pts

- Cervical cerclage

What is a bulging amnion?

Amnion extends into endocervical canal and vagina.

What is a cervical cerclage? When are they inserted?

Suture reinforcing cervical canal integrity inserted at 13-16 wk GA

What is a Mcdonald cerclage?

Purse-string suture around cervix at external os (TV approach)

What is a Shirodkar cerclage?

Suture placed in mid-section of cervix (TV approach)

What is an abdominal suture?

cerclage placed at level of internal os (TA approach)

What is a rescue cerclage? When is it performed?

- Performed when cervix dilates over 1-2 cm by physical exam/US

- Push the herniated membranes back into the uterine cavity and close cx w/ rescue stitch

- Performed as a last resort

What risks are associated with a rescue cerclage?

- Premature rupture of membranes when pushing back in

- Infection

TRUE or FALSE: Debris seen within a cervical funnel increases the risk of preterm birth.

TRUE: Debris within funnel indicates risk of preterm birth.