• Nathan Riley, MD

Obgyno Wino Podcast Episode 37 - Prediction and Prevention of Preterm Labor

Updated: Jan 26, 2020

"There is nothing sweeter, gentler or softer than water. But water has the power to move mountains." — Dame Claire Berschinger, Swiss nurse and activist

2018 Cabernet Sauvignon by 19Crimes

PB#130 - Published October 2012 (Reaffirmed in 2018)

Five Pearls

  1. Spontaneous preterm birth rates are decreasing with time (woohoo!)

  2. Good thing, because PTD at <34 wga carries higher mortality and morbidity risk to newborn in delivery and long-term morbidity

  3. In pregnant patients with a history of PTD, 17-OH-P supplementation should be recommended at 16-24 wga and continued through 36 wga

  4. In patients w/ singleton pregnancy and history of PTD, cerclage should be offered if CL <25 mm is detected on TVUS at <24 wga

  5. In patients without a history of PTD, an incidental CL of <20 mm may benefit from vaginal progesterone supplementation


- overall, rate of preterm delivery (PTD) has been decreasing with time due to improved prediction and prevention

- "Although risks are greatest for neonates born before 34 weeks of gestation, infants born after 34 weeks of gestation but before 37 weeks of gestation are still more likely to experience delivery complications, long-term impairment, and early death than those born later in pregnancy"

- risk factors for PTD: prior PTD (1-2x ↑ risk), short cervical length (<20mm if no history of PTD; <25mm if prior history), vaginal infection in pregnancy, vaginal bleeding in pregnancy, UTI in pregnancy, or periodontal disease in pregnancy (treatment of any of these won't normalize risk, though), low maternal BMI, smoking, substance abuse, and short interpregnancy interval

Who should be screened and how?

- really the only patients who qualify for screening are those with a history of prior PTD

- get a baseline transvaginal ultrasound (TVUS) and repeat this evaluation every 1-2 weeks to assess for change (limited data on time interval)

- measure three times, and go with the average

- "fetal fibronectin screening, bacterial vaginosis testing, and home uterine activity monitoring have been proposed to assess a woman’s risk of preterm delivery" and none of them have panned out as useful predictors of PTD in asymptomatic women

- recent data suggests that it might actually be cost-effective to universally screen for shortened cervix in patients without history of PTD (study 1, study 2), but, for now, ACOG states it's reasonable to offer but not necessarily recommended universally

How to properly measure cervical length on TVUS

When and how do we intervene for patients w/ a history of PTD?

- the purpose of screening is to identify patients in whom intervention will be helpful

- first off, if your patient is pregnant and has a history of PTD (<37 wga), you should recommend starting weekly injections of 17-OH-P between 16-24 wga (to be continued through 36 wga)

- CL <25 mm in a woman with history of PTD may be a candidate for cervical cerclage ("US-indicated cerclage"); **only applies to singletons

- cerclage in these patients decreased likelihood of PTD and perinatal death

- unclear if 17-OH-P plus cerclage are additionally helpful together compared to either intervention alone

- presence of funneling hasn't been found to significantly influence the risk of PTD

- "indomethacin or antibiotics, activity restriction, or supplementation with omega-3 fatty acids have not been evaluated in the context of randomized trials for women with short cervical length, and are not recommended as clinical interventions for women with an incidentally diagnosed short cervical length."

The various studies that have looked at progesterone supplementation for the prevention of PTD

What if a short cervix is found incidentally in a patient w/out history of PTD?

- If CL <20 mm is found incidentally in a woman without history of PTD, she may benefit from vaginal progesterone supplementation if detected at <24 wga; **only applies to singletons

- cerclage has been suggested but hasn't panned out in these patients who have no history of PTD

- cervical pessaries have actually been found to be promising in smaller studies, but we are still waiting for large studies

What about multiple gestation pregnancies?

- unfortunately neither vaginal progesterone nor cerclage have been found to be helpful in preventing PTD of twins or more

Another final word about cerclages...

- there are three indications:

  • Ultrasound-indicated: what we've already described

  • History-indicated: cerclage placed at conclusion of first trimester and after prenatal screening has been completed in patients with cervical insufficiency

  • Rescue cerclage: option if cervical dilation >2cm is visualized on speculum exam or found on ultrasound exam at <24 wga

- there are three types (all call for Mersilene suture):

  • McDonald: performed vaginally under regional anesthesia using the purse-string technique at the cervicovaginal junction; bladder emptying is recommended, but mobilization is not required

  • Shirodkar: performed vaginally under regional anesthesia using purse string technique after emptying and mobilizing the bladder

  • Transabdominal: performed laparoscopically or open, placing the suture in purse-string fashion at the cervicoisthmic jxn (**will require c-section); recommended if vaginal placement is determined not possible or if cervix is too short that vaginal effort is unlikely to be successful

- if a patient has a cerclage in place and presents in active labor, you must remove the cerclage to avoid cervical laceration, which can lead to outrageous brisk bleeding (you can't stop active labor)

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