Tests
Your Organizational Guidance
ebpracticenet urges you to prioritize the following organizational guidance:
Prévention de l’accouchement prématuré chez les femmes à risque – évaluation de quelques mesures courantesPublished by: KCELast published: 2014Preventie bij verhoogd risico op vroeggeboorte - evaluatie van een aantal courante interventiesPublished by: KCELast published: 20141st tests to order
nonstress cardiotocogram
Test
This is not a specific test for preterm labor but an initial step to establish wellbeing of the fetus.
Result
detection of fetal heartbeat
tocography
Test
The frequency of contractions can be documented on a trace. More than one contraction every 10 minutes is more significant, and preterm labor may be more likely.
Result
>1 contraction every 10 minutes
transvaginal ultrasound of the cervix
Test
Women who present with contractions prior to 37 weeks' gestation with a closed cervix should have a vaginal exam and transvaginal assessment (where available) of the cervical length. Cervical length can indicate the likelihood of imminent delivery as cervical lengths under 2 cm are associated with much higher risks of delivery (>60%).[53] Transvaginal assessment of cervical length has greater predictive value if performed in combination with the fetal fibronectin test.[28]
Result
significant if cervical length <2 cm
cervico-vaginal swab for fetal fibronectin
Test
All women presenting with preterm contractions between 24 and 35 weeks' gestation, who are not in advanced labor (cervical dilation <3 cm), should be considered to have a cervico-vaginal swab for fetal fibronectin. False positives can occur in the presence of vaginal bleeding, cervical cerclage, and cervical manipulation. In a systematic review, 20% of those with a positive fibronectin test deliver within 1 week compared with only 1% with a negative test.[93] A bedside test can also quantify fetal fibronectin, where the concentration correlates with risk: levels under 10 nanograms/mL are very low risk, and levels over 200 nanograms/mL give a 45% chance of delivering in 2 weeks.[104] The fetal fibronectin test has greater predictive value if performed in combination with transvaginal assessment of cervical length.[28][96][97] Its use is associated with reduced resource usage.[105] This test is also valuable in asymptomatic women who are at high risk of preterm labor.[106]
Guidance from NHS England recommends quantitative fetal fibronectin as it can be used in asymptomatic women and has better sensitivity than alternatives.[102]
Result
positive
CBC
Test
Women with threatened preterm labor should have a CBC. Results are nonspecific, but an elevated WBC is indicative of infection, and hemoglobin level should be checked in cases of suspected antepartum hemorrhage.
Result
decreased hemoglobin with prenatal hemorrhage; elevated WBC count in presence of infection
CRP
Test
Nonspecific, but recommended as part of the infection screen for all women with threatened preterm labor.
Result
elevated in presence of infection
urine dipstick
Test
Women who present with threatened preterm labor should have a urinalysis for proteinuria, leukocytes, and nitrites as part of the infection screen as a possible cause of preterm labor. Proteinuria may be seen in preeclampsia.
Result
positive in presence of infection
urine microscopy, culture, and sensitivity
Test
If urine dipstick is positive for leukocytes or nitrites, a midstream urine specimen should be sent for microscopy, culture, and sensitivities.
Result
positive growth in presence of infection
high vaginal/rectal culture
Test
A high vaginal and rectal culture can be taken to screen for group B streptococcus.[103] The presence is associated with preterm labor, but treatment does not affect outcome.
Result
positive in presence of group B streptococcus
Tests to consider
microscopy of vaginal fluid
Test
Diagnosis of preterm prelabor rupture of membranes (PPROM) is usually clinical. Vaginal fluid is examined after drying. False negatives are common.
Result
amniotic fluid crystallizes and may leave a fern-leaf pattern
Kleihauer blood test
Test
This blood test, evaluated in the laboratory for the presence of fetal cells, is usually used to detect fetal-maternal hemorrhage in rhesus-negative mothers in order to calculate how much anti-D is needed. A positive Kleihauer test in threatened preterm labor may indicate retroplacental bleeding as a cause of the preterm contractions, although the clinical utility of this is uncertain and not all clinicians perform this test.
Result
positive with fetal-maternal hemorrhage
urine toxicology screen
Test
A urine toxicology screen may be indicated if recreational drug use is suspected, as cocaine can induce preterm labor. It should be noted that such a screen is not definitive for the detection of recreational drugs.
Result
positive if cocaine has been taken
insulin-like growth factor binding protein-1 (IGFBP-1) test
Test
This is a bedside immunochromatographic dipstick test that detects the presence of the phosphorylated form of IGFBP-1 in cervical secretions. It is an alternative to the fetal fibronectin test. A positive test result is shown as 2 blue lines - a control line and a test line in the result area. If only the control line has appeared after 5 minutes, the test result is negative. This has also been used to confirm preterm prelabor rupture of membranes (PPROM) with sensitivities of over 90% and specificities over 98%.[99] This test is unavailable in the US.
The UK National Institute for Health and Care Excellence recommends that IGFBP-1 may be used to help guide management for suspected PPROM if amniotic fluid is not visible, but suggests evidence is insufficient for routine use to diagnose preterm labor in women with intact membranes.[71][101]
Result
positive
placental alpha microglobulin-1 (PAMG-1)
Test
May be used to determine the risk of delivery in women with threatened preterm labor who have intact membranes.[100] This test is performed by taking a low vaginal swab and inserting the test strip into a small tube that indicates a positive or negative result.
The UK National Institute for Health and Care Excellence recommends that PAMG-1 may be used to help guide management for suspected preterm prelabor rupture of membranes (PPROM) if amniotic fluid is not visible, but suggests evidence is insufficient for routine use to diagnose preterm labor in women with intact membranes.[71][101]
Result
positive
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