How to evaluate for preterm labor?

From the Guidelines

Evaluating for preterm labor requires a thorough assessment of symptoms, risk factors, and physical examination findings, with transvaginal ultrasound being the preferred imaging modality for assessing the gravid cervix, as recommended by the American College of Radiology Appropriateness Criteria 1. To evaluate for preterm labor, the following steps should be taken:

• Ask about symptoms such as regular uterine contractions, pelvic pressure, low back pain, increased vaginal discharge, or vaginal bleeding
• Perform a physical examination including vital signs, abdominal palpation for uterine tenderness or contractions, and a sterile speculum examination to assess for cervical dilation, effacement, and amniotic fluid leakage using nitrazine paper and fern testing
• Use transvaginal ultrasound to measure cervical length, with measurements less than 25mm indicating increased risk, as supported by studies such as those published in the Journal of the American College of Radiology 1
• Utilize electronic fetal monitoring to assess contraction frequency and fetal heart rate patterns
• Conduct laboratory tests, including a complete blood count, urinalysis, and cervicovaginal fetal fibronectin testing in women between 24-34 weeks with intact membranes, as recommended by the American College of Obstetricians and Gynecologists 1
• Consider risk factors such as previous preterm birth, multiple gestation, cervical insufficiency, uterine anomalies, and infections
• Transvaginal ultrasound is the preferred approach for assessing the gravid cervix in cases of suspected preterm labor, due to its high negative predictive value and ability to measure cervical length accurately 1. If preterm labor is confirmed, management may include tocolytic medications, antenatal corticosteroids to accelerate fetal lung maturity, and possibly magnesium sulfate for neuroprotection, as discussed in the American Journal of Obstetrics and Gynecology 1.

From the FDA Drug Label

The administration of magnesium sulfate outside of its approved indication in pregnant women should be by trained obstetrical personnel in a hospital setting with appropriate obstetrical care facilities The FDA drug label does not answer the question.

From the Research

Evaluation for Preterm Labor

To evaluate for preterm labor, several steps can be taken:

• Clinical criteria and physical examination are essential for diagnosis 2
• Measurement of cervical length (CL) with transvaginal ultrasound (TVUS) is a key diagnostic tool 2, 3, 4
• Biomarkers, such as fetal fibronectin testing, can also be used to aid in diagnosis 2
• Ultrasonographic examination of the cervix can provide valuable information on cervical length and internal os 3
• A short cervical length, typically less than 25 mm, is predictive of preterm birth 4

Diagnostic Criteria

Diagnostic criteria for preterm labor include:

• Cervical changes associated with regular painful uterine contractions between 22 and 36 weeks + 6 days 3
• A short cervical length, typically less than 25 mm 4
• Funneling of the cervical canal may also be a predictive factor 3, 4

Screening and Prevention

Screening for preterm labor can be done through:

• TVUS CL measurement between 16 and 24 weeks of gestation 2
• Vaginal progesterone or cervical cerclage may be used to prevent preterm labor in certain cases 2, 4
• Cervical pessary is not recommended as a preventive measure 2

Management

Management of preterm labor involves:

• Tocolytics, antenatal corticosteroids, and magnesium sulfate to delay delivery and improve outcomes 2, 5
• In utero transfer to a higher care facility may be necessary in some cases 2
• Routine cesarean delivery is not recommended for preterm labor 2