New Preterm Birth Risk Guidelines Address Cervical Length

Laurie Barclay, MD

March 23, 2012

March 23, 2012 — Two new clinical guidelines address taking cervical length measurements to help determine risk for preterm birth, as well as using progesterone and other treatments for women found to be at increased risk. Recommendations from the Society for Maternal-Fetal Medicine (SMFM) were published online March 19 in the American Journal of Obstetrics and Gynecology, and those from the American College of Obstetricians and Gynecologists (ACOG) were published as a committee opinion.

"Premature birth...is the leading cause of infant death and many severe disabilities," Thomas J. Garite, MD, editor-in-chief of the American Journal of Obstetrics and Gynecology, told Medscape Medical News. "Twelve percent of babies are born too soon in the US, and we have the second highest rate of prematurity among developed nations in the world. This is a very serious public health problem."

Annual costs for preterm birth exceed $26.2 billion in the United States. Worldwide, preterm birth results in 1 million deaths each year, making it the leading cause of infant morbidity and mortality in developed countries.

The new guidelines aim to provide clinicians with evidence-based recommendations to identify and treat pregnant women who are at high risk for premature birth.

"Prematurity has long been one of the biggest challenges in obstetrics because we haven't had any way to help the patients at highest risk," said Dr. Garite, who is also professor emeritus and past EJ Quilligan Chair of Obstetrics and Gynecology at the University of California, Irvine, and director of Research for Obstetrics at Pediatrix Medical Group. "Now we do: Progesterone is proven to help prevent premature birth for some women."

Overview of SMFM Recommendations

Specific observations and recommendations in the SMFM Guidelines include the following:

  • Evidence is convincing that use of progesterone is associated with lower risk for preterm birth in some pregnant women, as well as with better neonatal outcomes.

  • Pregnant women in whom the cervix is prematurely short are at high risk for preterm delivery and should be treated with vaginal progesterone.

  • While there are barriers to implementing a universal cervical length screening policy, the document offers detailed guidelines to help individual clinicians start using this risk assessment strategy immediately.

  • Cost-effectiveness studies have shown that cervical length screening is associated with lower overall costs and improved neonatal health. The SMFM Guidelines therefore recommend that third-party payers cover the cost of cervical length measurement to evaluate risk for preterm birth.

  • Because of the high prevalence and public health burden of preterm birth, experts recommend universal cervical length measurement, which meets World Health Organization criteria for an effective screening test.

"The significance of these new SMFM and ACOG guidelines is tremendous," Dr. Garite said. "We've known for decades that pregnant women with a prematurely short cervix are at very high risk for potentially tragic early deliveries. But without a way to treat that problem, there was no justification for looking for it. Now that there is enough evidence that progesterone helps solve that problem, it's time to go find and treat it."

SMFM Evidence Base

A search of PubMed identified relevant English-language publications of randomized trials and other studies assessing the efficacy of progestogens (vaginal progesterone and 17-alpha hydroxyl-progesterone caproate [17P]) in preventing preterm birth. The reviewers also searched the Cochrane Library, organizational guidelines, and reference lists of identified studies.

The reviewers analyzed the data separately for singleton vs multiple gestations, previous history of preterm birth, or short cervical length measured by transvaginal ultrasound (TVU), as well as for combinations of these risk factors.

Findings from randomized trials suggest that women with singleton gestations, no prior preterm birth, and short cervical length not exceeding 20 mm at 24 weeks or before can be offered vaginal progesterone supplied as 90 mg gel or 200 mg suppository. This treatment is linked to lower rates of preterm birth and perinatal morbidity and mortality.

The reviewers note that to prevent preterm birth, universal cervical length screening of singleton gestations in women without a previous history of preterm birth is still controversial and cannot yet be universally mandated. However, it could be reasonable for individual practitioners to consider implementing such a screening strategy, following strict guidelines.

Both women with singleton gestations and those with prior preterm birth at from 20 to 36 6/7 weeks should receive 17P 250 mg intramuscularly weekly, preferably starting at 16 to 20 weeks, until 36 weeks of gestation. If these women experience cervical length shortening to less than 25 mm before 24 weeks' gestation, as determined by TVU, cervical cerclage may be offered.

There is insufficient evidence to recommend the use of progestogens in women with multiple gestations in the current pregnancy, preterm labor, or preterm premature rupture of membranes, regardless of cervical length.

"The SMFM and ACOG publications include identical guidance for physicians to offer specific formulations of progesterone as a preventive therapy for 2 of the highest-risk patient groups: those with a short cervix and those with a history of prior preterm birth," Dr. Garite said. "Prior to cervical length screening, there was great difficulty in identifying in advance the majority of women who were at risk for premature delivery. This was especially true in women having their first baby, as history of a prior preterm birth could obviously not be used in this group."

Overview of ACOG Committee Opinion

  • ACOG and the American Institute of Ultrasound in Medicine recommend a cervical length measurement at around 18 to 22 gestational weeks, at the same time as the ultrasound for fetal anatomic survey, because this is a useful screening test to predict spontaneous preterm birth.

  • Women with cervical length less than 25 mm at 14 to 28 weeks should undergo a subsequent TVU to confirm this finding.

  • Women in whom short cervical length is confirmed should have a review of risk factors for preterm birth, as well as of management options.

  • TVU measurement of cervical length should be performed only when interventions to reduce risk for preterm birth are available.

  • The utility of universal cervical length screening to prevent preterm birth is still controversial and under debate.

"It's important to recognize that neither of these publications recommends mandatory transvaginal cervical length screening for all pregnant women at this time," Dr. Garite said. "For now, it is up to individual physicians to decide whether or not to assess preterm birth risk with cervical length measurements. The SMFM guidelines note that it's reasonable to do so for singleton pregnancies, provided that recommendations for quality control, patient types, and treatments are followed."

Barriers to Universal Cervical Length Screening

The SMFM clinical guideline notes that lack of availability of TVU is a significant barrier to universal cervical length screening using this technology.

"This is expensive, high-tech equipment typically reserved for patients known to be at high risk," Dr. Garite said. "Expanding use to all singleton pregnancies would far exceed the ability of currently available TVU to meet the need. There just isn't enough TVU to go around right now."

Training in proper TVU technique and interpretation is essential for accurate measurement. Although TVU training is not universally available, the Perinatal Quality Foundation, which is related to the SMFM, is establishing a training program specifically for proper technique in TVU cervical length measurement.

"A simple new device, called CerviLenz, can provide a reliable cervical length measurement during any prenatal visit without ultrasound," Dr. Garite noted. "This disposable device holds promise for helping implement a risk assessment strategy where TVU is not readily available for all pregnant women. That means that more physicians can start using cervical length to identify high-risk patients for preventive treatment right away."

Use of this device may allow selective use of TVU for the small percentage of patients most likely to have a short cervix. Research has shown good correlation between CerviLenz and TVU measurements. One strategy is to start with a CerviLenz measurement and then only refer those patients who appear to have a short cervix to specialty centers for TVU measurement.

"This strategy can reduce the number of TVU exams and save time and money while still finding most of the high-risk patients for treatment, which would result in bigger cost savings," Dr. Garite said. "Our healthcare system can already handle the volume of TVU exams necessary for suspected or known high-risk patients. It's when we start talking about universal TVU exams that demand will exceed supply."

Although the SMFM guidelines recommend reimbursement by third-party payers for cervical length measurements, paying for TVU screening for all singleton pregnancies is still a significant barrier. This should be counterbalanced by the costs of premature birth, which can account for up to half of all pregnancy costs.

According to Dr. Garite, cost-effective analyses have shown that TVU cervical length measurements done once midgestation for all singleton pregnancies to identify and treat patients with a prematurely short cervix can save many millions, or even billions, of dollars if done in all pregnant women. This risk assessment and prevention strategy will also save lives.

"The expenses of neonatal intensive care when babies are born very early can be incredibly high," Dr. Garite said. "So too can be the costs of ongoing care for premature babies who have ongoing developmental disabilities or medical needs. For every treated high-risk patient who delivers at term instead of early, payers will save a tremendous amount of money, and more importantly, more moms will have healthier babies."

Each member of the Publications Committee of the SMFM submitted a conflict of interest disclosure delineating personal, professional, and/or business interests that might be perceived as a real or potential conflict of interest in relation to the guidelines publication. The ACOG opinion authors have disclosed no relevant financial relationships.

Am J Obstet Gynecol. Published online March 19, 2012. Full text

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