A Comparison of Speculum and Non-speculum Collection Methods of Cervicovaginal Specimens for Fetal Fibronectin Testing
Abstract & Commentary
By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationship to this field of study.
Synopsis: A simpler method to collect fetal fibronectin specimens is just as effective as the more elaborate standard method.
Source: Stafford IP, et al. A comparison of speculum and nonspeculum of cervicovaginal specimens for fetal fibronectin testing. Am J Obstet Gynecol 2008;199:131.e1-131.e4.
Fetal fibronectin is now being used in many hospitals to separate out those with preterm contractions (PTCs) who are in true labor from those with contractions who are not (and, therefore, not requiring tocolytics or hospitalization). However, the method to obtain a sample for analysis is somewhat cumbersome, requiring a speculum examination and careful placement of a cotton (or polyester) swab into the posterior fornix under direct visualization.
In this study, conducted in Mexico, two simpler methods of obtaining the specimen were tested against the above gold standard technique: 1) a single finger guided method to reach the posterior fornix, and 2) a blind insertion of the swab into the posterior fornix. Obviously, neither method requires insertion of a speculum or elaborate patient positioning.
In the first portion of the study, 169 paired samples were analyzed for fetal fibronectin (fFN) in women who were between 22 and 42 weeks gestation. All had samples obtained by the speculum method, as well as a nonspeculum approach, in which a single finger was used to depress the perineum, and the swab was advanced over the finger, acting as an introducer. In the second part of the study, involving paired samples from an additional 35 patients, the swab was simply directed posteriorly through the introitus until resistance was encountered, where the sample was obtained. The specimens obtained in this manner were compared with those obtained with the speculum method. In part one of the study, the fFNs were analyzed via a standard rapid test, and in part two this was done by a batched ELISA assay.
In part one, 54 patients tested positive with both methods and 107 patients tested negative with both methods. There were discrepancies between the two methods in only 8 instances, giving a 95% agreement. In part two the authors were able to quantify the fFN results and there was discordance in only one case. The quantitative correlation between methods was excellent (0.97).
One might say that reviewing this paper represents wallowing in minutia. However, I would counter that this study provides very usable information that will not only save time in evaluating patients with questionable preterm labor, but also will diminish patient discomfort.
There are data now in the literature to validate the concept of using either fFN or cervical length (CL) to rule out preterm labor in patients with PTCs. For example, two studies have shown that if patients with this clinical backdrop had a CL by transvaginal sonography of >1.4 cm, they had only a 1%-2% chance of delivering within a week of the exam.1,2 Another study showed that if the CL was >3 cm, 100% of these patients delivered after 34 weeks.3 Fetal fibronectin seems to perform about as well as CL in some studies, but when the two are used together, the predictive ability to include or exclude patients destined to have preterm delivery (PTD) is improved even further. For example, in a collaborative study from Chile and Detroit, the investigators showed that CL was slightly better than fFN at predicting PTD at less than 35 weeks, occurring in 20% of the 215 patients studied with PTCs.4 However, if both were positive, 81% delivered before 35 weeks, and if both were negative, only 2% delivered within a week of the exam, and none had a PTB <32 weeks. Most importantly, if the CL exceeded 2.9 cm, the fFN added no diagnostic value.
So, since the fFN adds extra cost to a workup that is already quite expensive, it seems from all the above information that a pragmatic approach to patients being evaluated for PTCs would be first to gently introduce the swab blindly into the patient's posterior fornix, and to set it aside, pending the results of a CL examination to follow (which might falsely affect the results of the fFN, if done first). If the CL is >2.9 cm, no further studies would be required, and the patient could be discharged. If the CL were between 1.5 cm and 3.0 cm, then the fFN specimen could be sent off for analysis, and if it is negative, the patient could be discharged. Also, if the cervix is <1.5 cm, the fFN would add little to the management, since these patients have a large enough chance of delivery that hospitalization would be warranted.
This simple approach would save precious time and money, and would diminish patient discomfort and anxiety.
- Tsoi E, et al. Ultrasound assessment of cervical length in threatened preterm labor. Ultrasound Obstet Gynecol 2003;21:552-555.
- Fuchs IB, et al. Sonographic cervical length in singleton pregnancies with intact membranes presenting with threatened preterm labor. Ultrasound Obstet Gynecol 2004;24:554-557.
- Daskalakis G, et al. Cervical assessment in women with threatened preterm labor. J Matern Fetal Neonatal Med 2005;17:309-312
- Gomez R, et al. Cervicovaginal fibronectin improves the prediction of preterm delivery based on sonographic cervical length in patients with preterm uterine contractions and intact membranes. Am J Obstet Gynecol 2005;192:350-359.