Transvaginal Cervical Length Assessment
Preterm birth (delivery of the baby before 37 weeks into the pregnancy) occurs in about 1 in 7 pregnancies. The rate is much higher with twins, where more than 50 percent of women deliver before 36 weeks, and even higher with triplets, where more than 50 percent of women deliver before 33 weeks.
Assessment of the cervical length by ultrasound can be very helpful in assessing women for preterm delivery risk. For example, all women with prior cervical surgery may be at increased risk to have weakness of the cervix due to the surgery, which can result in very premature delivery. We can assess for this with transvaginal cervical length assessment.
A woman who has had a prior premature baby is typically seen every couple of weeks, starting several weeks before the preterm baby was born, to make sure that the cervical length is staying normal. A drop in cervical length, or an abnormal appearance to the internal contours of the cervix, can be an early warning system for threatened preterm labor, and, oftentimes, we can recommend interventions to reduce the chance that the baby delivers early.
Both ACOG and SMFM are now recommending routine transvaginal cervical length screening for both high and low risk women in pregnancy (SMFM Consult Series #40: The role of routine cervical length screening in selected high and low risk women for preterm birth prevention).
Because interventions that reduce the risk of spontaneous preterm birth are available and effective in selected patients with short cervical length, at San Diego Perinatal Center, we are now routinely offering this screening to all patients who are scanned between 16 and 30 weeks gestation. Vaginal progesterone and exam indicated cerclage are two examples of interventions that have been proven effective in appropriately screened patients to reduce preterm birth. Although not mandatory, we believe this screening is an important addition to the high quality screening ultrasounds we are already providing to your patients. In addition to routine screening for cervical length for preterm birth prevention, transvaginal scans are important in screening for abnormal placentation (placenta accreta or vasa previa). The prenatal identification of invasive placentation and vasa previa can also improve maternal and fetal outcome by allowing appropriately timed and managed deliveries.