28 OBSTETRICS S E P T E M B E R 2 0 1 1 • O B . G Y N . N E W S

New Test Eyed for Ruling Out Preterm DeliveryB Y S U S A N L O N D O N

FROM THE ANNUAL MEETING OF THE

SOCIETY OF OBSTETRICIANS AND

GYNAECOLOGISTS OF CANADA

VANCOUVER, B.C. – The phospho-rylated insulinlike growth factor bind-ing protein–1 test may edge out the fe-tal fibronectin test when it comes topredicting preterm delivery, a studyhas shown.

In the prospective cohort studyamong 349 women with symptoms ofpreterm labor, the two tests had simi-larly good negative predictive values,0.86 and 0.88, researchers reported atthe meeting. Both had poor sensitivityand positive predictive values.

However, the phosphorylated in-sulinlike growth factor binding pro-tein–1 (ph IGFBP-1) test (marketed out-side the United States as the Actim

Partus test) costs about one-fourth asmuch as the fetal fibronectin test. Also,the former is a simple dipstick test thatcan be run at the bedside, and it differsin not being affected by recent inter-course or vaginal examinations.

The Actim Partus test is not cur-rently available in the United States.“The timeline for its clearance andavailability in the United States is …not yet known,” according to a spokes-

Major Finding: The negative predictivevalues for preterm delivery were simi-larly high for ph IGFBP-1 and fetal fi-bronectin; the positive predictive val-ues were poor for both.

Data Source: A prospective cohortstudy among 349 women with symp-toms of preterm labor.

Disclosures: Dr. Cooper reported that shehad no relevant financial disclosures.

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woman for Medix Biochemica, Kauni-ainen, Finland.

“The Actim Partus compares favor-ably to fetal fibronectin for the ability torule out preterm labor,” said lead inves-tigator Dr. Stephanie Cooper, programdirector of maternal-fetal medicine atthe University of Calgary (Alta.). “Giv-en the benefit of reduced cost, efficien-cy, and ability to use it in a broad clini-cal scenario, institutions should considerusing the newer test, the Partus test, un-til better tools are available.”

Her institution has not yet switched tothe new test. “But what I will say is these

results definitely make me do fetal fi-bronectin less,” she commented. “I don’tthink Partus is a good test, I don’t thinkfibronectin is a good test. … I’m hopingthat there’s going to be a better test.”

Fetal fibronectin is generally regarded asthe gold standard for predicting pretermdelivery, according to Dr. Cooper.

However, “it is not a perfect test. Infact, maybe it’s more like the bronzestandard,” she commented. Its limita-tions include a poor positive predictivevalue; false-positivity in women whohave recently had a vaginal exam or in-tercourse; cost; and, usually, the need

for a laboratory for analysis.“Ph IGFBP-1 is released by the cervix

following disruption of the choriodecid-ual barrier, which we believe occurs withthe onset of labor,” she explained. It hasshown promise for overcoming some ofthe limitations of the fetal fibronectintest.

The researchers enrolled in the study349 women who had symptoms of laborpreterm (between 24 and 34 weeks’ ges-tation) and no contraindications to vagi-nal examination.

Women were ineligible if they hadruptured membranes, had antepartum

hemorrhage, were in active labor (de-fined as having a cervix diameter ofgreater than 3 cm), or had suspectedchorioamnionitis.

All of the women received routinecare. A swab for fetal fibronectin testingwas obtained according to usual proto-col; per institutional procedure at thetime, the swab was kept for 2 hours andanalyzed only if symptoms of laborwere still equivocal.

A cervical swab was obtained for phIGFBP-1 measurement with the ActimPartus test. Patients who were ineligiblefor a fetal fibronectin test because of arecent vaginal examination or inter-course still had this test. All of theseswabs were analyzed by a study regis-tered nurse who was blinded to the pa-tient’s clinical course.

The women were 29 years old, on av-erage. The mean gestational age was29.8 weeks. Forty-three percent werenulliparous, and 16% had previously ex-perienced a preterm birth. Three-fourths had a cervical dilation on ad-mission of 0-1 cm.

Swabs were processed for ph IGFBP-1 in all 349 women, but for fetal fi-bronectin in only 288 of them. In otherwords, 17% of the women did not havethe latter test run either because theywere ineligible because of recent vagi-nal examination or intercourse or be-cause labor was no longer equivocal af-ter the 2-hour wait.

Overall, 26% of the ph IGFBP-1 testresults were positive (had a value of atleast 10 mcg/L), and 8% of the fetal fi-bronectin test results were positive (hada value of at least 50 ng/mL).

Only 16% of the women were deliv-ered preterm (before 37 weeks’ gesta-tion). “This just goes to show that themajority of patients who present withpreterm labor actually will not deliverpreterm,” Dr. Cooper commented.

The ph IGFBP-1 test and the fetal fi-bronectin test had similarly good nega-tive predictive values for preterm deliv-ery (0.86 and 0.88).

The positive predictive value was poorfor both, although somewhat more sofor ph IGFBP-1 (0.22 and 0.54).

The ph IGFBP-1 test and the fetal fi-bronectin test also both had poor sensi-tivity (39% and 33%), while specificitywas marginally poorer for the formertest (74% and 95%).

The investigators also assessed theperformance of the two tests combined.“There were times when they agreedand times when they didn’t agree, but itdidn’t seem to be that combining themtogether improved your predictability,”she said.

Recent data suggest that predictabili-ty may improve when a biochemicalmarker is combined with cervical lengthon ultrasound, noted Dr. Cooper.

“The problem is, we are looking fora rapid bedside test for people in ruralareas who don’t have resources,” shecommented. “So if we start puttingcervical length into the mix, then ittakes away the primary objective ofhow do we help people who are livingin rural areas that are rural enough tohave to make decisions about clinicaltransfer.” ■