Do pregnancies complicated by preterm birth with a negative fetal fibronectin screen have different characteristics compared to those that have positive fetal fibronectin results?
Belisle, Elisabeth Suzanne
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Objective: The fetal fibronection (fFN) test is an excellent test to rule out preterm birth (PTB) as it has a negative predictive value of 98-99%. However, some patients in this group of women still deliver preterm, which puts the infant at risk for many chronic complications such as cerebral palsy and developmental delay. To date, there is limited data about PTB in the setting of a negative fFN. The purpose of this study is to look at maternal, fetal, and placental characteristics of women who had a spontaneous preterm delivery (PTD) with a negative fFN test and compare them with maternal, fetal, and placental characteristics of women who had a spontaneous PTD with a positive fFN test. Methods: This retrospective chart review was conducted at Baystate Medical Center between 2006 and 2009. Women were included in the study if they delivered within 14 days of the fFN test at this institution. Demographic characteristics, clinical antecedents for delivery, and placenta pathology reports were compared between women with a positive fFN test and a negative fFN test. Clinical antecedents for delivery were either (a) Preterm premature rupture of membranes (PPROM) leading to preterm labor (PTL) (b) abruption leading to PTL or (c) idiopathic PTL. Placenta histological reports were reviewed and organized into the following categories (a) normal placenta (b) evidence of inflammation (c) evidence of ischemic changes or (d) evidence of both inflammation and ischemic changes. Comparison between groups was conducted using Wilcoxon rank sum test and Fisher's exact test. Results: A total of 82 women had fFN testing and delivered preterm. Of these, 58 women had spontaneous PTL and a placental pathology report. Demographic characteristics were found to be similar between the two groups. Women with a positive fFN test were found to deliver earlier (p=0.038). Overall, there was a trend toward an increase in placental ischemic changes in the fFN negative group (68.8% versus 23.8%) but this did not achieve statistical significance. Conclusion: Women delivering spontaneously preterm after a positive fFN test may have different pregnancy characteristics than women delivering spontaneously preterm after a negative fFN test. Women in the positive fFN test group tended to deliver earlier than women in the negative fFN test group, suggesting that the mechanism contributing to PTB is likely to be different between the two groups. The data suggests that there is a trend toward women with a negative fFN having placental ischemic changes. More studies should be done to see if this trend continues. Clinically, this information would be helpful because these women may not be a good candidate for this test and may need to be hospitalized and given steroid treatment when showing signs of PTL. However, until further information is available, women with suspected ischemic placentas should not yet be excluded from fFN testing. Clearly, further studies are needed to explore the relationship between placental ischemia and fFN testing.