Evaluation of a Novel Diagnostic Kit for the Detection of Placental Alpha-Microglobulin-1 in the Prediction of Preterm Birth

Background

Placental alpha microglobulin-1 (PAMG-1) is a protein found in high concentrations in amniotic fluid but very low concentrations in background levels of cervico-vaginal discharge. In recent years, the medical community has increasingly accepted the widespread use of detecting PAMG-1 to aid the provider in confirming or ruling out rupture of the fetal membranes (ROM). The test used is commercially marketed as the AmniSure® ROM Test, manufactured by AmniSure® International, LLC, Boston, MA, USA.

In one of the original investigations of PAMG-1 for the detection of ROM, Lee et al. noted that in 20 out of the 23 cases where the AmniSure® ROM Test was positive and standard clinical assessment (i.e. nitrazine, ferning and pooling) was negative, the patient was ultimately determined to have been ruptured upon retrospective analysis of their clinical course. It was later reported that for all of the preterm patients in this group that showed signs and symptoms of labor, delivery followed within 7 days. In 2011, the clinical value of a positive AmniSure® ROM Test in the patient presenting with signs and symptoms of preterm labor (PTL) but without membrane rupture was investigated by this same group. The results demonstrated that the AmniSure® ROM Test was highly predictive of delivery of these patients within 48 hours, 7 days and 14 days.

In the patient group on whom the above tests are performed, membrane rupture is excluded as this condition, if present, confirms imminent delivery and dictates a different course of management. It has been demonstrated that the AmniSure® ROM Test can detect PAMG-1 in patients presenting with signs and symptoms of ROM when all other traditional methods are unable to do so. The likelihoods of adverse outcomes associated with these sub-clinical ruptures have been demonstrated to not be statistically different from the adverse outcomes associated with gross or clinically detectable ruptures. The proposed physiological explanation for this phenomenon is that PAMG-1 is released through micro-perforations of the amniotic membranes that more copious amounts of fluid cannot pass through.

The major difference, however, between the patient presenting with signs of preterm labor and those just described above is the presence, or absence, of membrane rupture signs or complaints. Given that the complaints of ROM are typically rooted in an overt episode of suspicious fluid leakage, it is hypothesized that the resulting concentration of PAMG-1 in the vagina of the patient without such overt complaints or signs of ROM will be lower than the current sensitivity threshold of the AmniSure® ROM Test.

Accordingly, a device that is more sensitive in its detection of PAMG-1 than the AmniSure® ROM Test presumably will be able to detect more patients at risk for imminent delivery than its predecessor in patients presenting to labor and delivery units with signs, symptoms or complaints suggestive of preterm labor (PTL) who have no clinical evidence of membrane rupture. If this is the case, this tool may be of significant value to the provider in deciding how to manage their patients suspected to be at risk for imminent delivery. Management options may include administration of tocolytics to prolong gestation, corticosteroids to improve respiratory development, administration of antibiotics to decrease the risk of infection (intra-partum and post-partum), prescription of bed rest, as well as increased observation and fetal monitoring.

Currently, the American College of Obstetricians and Gynecologists (ACOG) indicate in their most recent Practice Bulletin on the Management of Preterm Labor that many tests to identify women at risk of preterm birth have been proposed and evaluated; however, only ultrasonography and fetal fibronectin testing have been shown to have benefit. Ultrasonography to determine cervical length, fetal fibronectin testing, or a combination of both may be useful in determining which women are at high risk for preterm delivery. However, their clinical usefulness may rest primarily with their ability to identify women who are least likely to deliver (i.e. their negative predictive value). Therefore, there is an urgent need for a test with a high positive predictive value in order to accurately predict imminent delivery to allow for salutary intervention.

Objective

1. To assess the efficacy of the novel kit for the detection of PAMG-1 in the cervico-vaginal secretions of pregnant women with clinically intact membranes presenting with signs and symptoms of PTL in predicting time-to-delivery. Assessment will be stratified by the following gestational age ranges:

   1. 24-31 6/7 weeks
   2. 32-36 6/7 weeks
2. To compare the results of the novel kit for the detection of PAMG-1 in pregnant women presenting with signs of PTL to a control group of pregnant women with the same gestational age without any symptoms and without an elevated risk of preterm birth.

3. To compare the novel kit for the detection of PAMG-1 to other methods available in assessing time to delivery in the same patient population, including:

   1. cervical length measurements by trans-vaginal ultrasound
   2. cervical dilatation > 1 cm
   3. Contraction Frequency ≥ 6 per hour (one every 10 min)
4. Determine the association between the results of the kit, cervical length and neonatal outcomes.

Methods

1. Study group: Patient presenting with symptoms of PTL between 24 and 36 6/7 weeks of gestation signs informed consent.

   Control group: Patient presenting for routine pregnancy control without any symptoms of PTL is between 24 an 36 6/7 weeks of gestation signs informed consent.

2. Specimen for the PAMG-1 test is collected in accordance with manufacturer's recommendations. During the same examination the physician takes a vaginal microbiological smear.
3. The sample is labeled and stored for later examination by a separate investigator who will not know the results of the physician's regular clinical evaluation.
4. After the physician completes their physical examination of the patient.
5. Cervical length measurement by transvaginal ultrasound (TVU) is performed.
6. Patient delivery data (e.g. time, condition, etc.) are recorded in the follow up.