Which Factors Contribute to False-Positive, False-Negative, and Invalid Results in Fetal Fibronectin Testing in Women with Symptoms of Preterm Labor?

Objective We assessed the influence of external factors on false-positive, false-negative, and invalid fibronectin results in the prediction of spontaneous delivery within 7 days. Methods We studied symptomatic women between 24 and 34 weeks' gestational age. We performed uni- and multivariable logistic regression to estimate the effect of external factors (vaginal soap, digital examination, transvaginal sonography, sexual intercourse, vaginal bleeding) on the risk of false-positive, false-negative, and invalid results, using spontaneous delivery within 7 days as the outcome. Results Out of 708 women, 237 (33%) had a false-positive result; none of the factors showed a significant association. Vaginal bleeding increased the proportion of positive fetal fibronectin (fFN) results, but was significantly associated with a lower risk of false-positive test results (odds ratio [OR], 0.22; 95% confidence intervals [CI], 0.12-0.39). Ten women (1%) had a false-negative result. None of the investigated factors was significantly associated with a significantly higher risk of false-negative results. Twenty-one tests (3%) were invalid; only vaginal bleeding showed a significant association (OR, 4.5; 95% CI, 1.7-12). Conclusion The effect of external factors on the performance of qualitative fFN testing is limited, with vaginal bleeding as the only factor that reduces its validity.

Risk stratification with cervical length and fetal fibronectin in women with threatened preterm labor before 34 weeks and not delivering within 7 days.

OBJECTIVE: To stratify the risk of spontaneous preterm delivery using cervical length (CL) and fetal fibronectin (fFN) in women with threatened preterm labor who remained pregnant after 7 days. DESIGN: Prospective observational study. SETTING: Nationwide cohort of women with threatened preterm labor from the Netherlands. POPULATION: Women with threatened preterm labor between 24 and 34 weeks with a valid CL and fFN measurement and remaining pregnant 7 days after admission. METHODS: Kaplan-Meier and Cox proportional hazards models were used to estimate cumulative percentages and hazard ratios (HR) for spontaneous delivery. MAIN OUTCOME MEASURES: Spontaneous delivery between 7 and 14 days after initial presentation and spontaneous preterm delivery before 34 weeks. RESULTS: The risk of delivery between 7 and 14 days was significantly increased for women with a CL < 15 mm or a CL ≥15 to <30 mm and a positive fFN, compared with women with a CL ≥30 mm: HR 22.3 [95% confidence interval (CI) 2.6-191] and 14 (95% CI 1.8-118), respectively. For spontaneous preterm delivery before 34 weeks the risk was increased for women with a CL < 15 mm [HR 6.3 (95% CI 2.6-15)] or with a CL ≥15 to <30 mm with either positive fFN [HR 3.6 (95% CI 1.5-8.7)] or negative fFN [HR 3.0 (95% CI 1.2-7.1)] compared with women with a CL ≥ 30 mm. CONCLUSIONS: In women remaining pregnant 7 days after threatened preterm labor, CL and fFN results can be used in risk stratification for spontaneous delivery.

What is the risk of preterm delivery after arrested preterm labor?

OBJECTIVE: The aim of this study is to assess if women with arrested preterm labor (PTL) have an increased risk of preterm delivery (PTD) compared with healthy pregnant women, and if digital examination, fetal fibronectin (fFn) and cervical length (CL) are prognostic markers for PTD after arrested PTL. STUDY DESIGN: Prospective-matched cohort study among women with arrested PTL (cases) and healthy pregnant women (controls). RESULTS: We included 74 index cases and 74 controls. PTD occurred in 20 (27%) index cases and in 5 (7%) controls (hazard ratio [HR], 4.5; 95% confidence interval [CI], 1.7-12). A dilatation of the cervix ≥ 1 cm (HR, 9.1 [95% CI, 3.3-25], an fFn positive status (HR, 13 [95% CI, 4.3-40]), and a CL < 15 mm (HR, 11 [95% CI, 3.1-38]) increased this risk in cases compared with controls. Knowledge of the fFn result had additional value over the cervical dilatation or CL in the prediction of persistent PTD, with an increased risk in case of a positive fFn test. CONCLUSION: Women stay at increased risk for PTD after arrested PTL. This risk further increased in case of ≥ 1 cm cervical dilatation, CL < 15 mm and/or a positive fFn status.

Randomized comparison of nifedipine and placebo in fibronectin-negative women with symptoms of preterm labor and a short cervix (APOSTEL-I Trial).

OBJECTIVE: To evaluate whether tocolysis with nifedipine can be omitted in women with symptoms of preterm labor, a shortened cervix, and negative fetal fibronectin test. STUDY DESIGN: A randomized noninferiority trial was performed in all Dutch perinatal centers. Women with symptoms of preterm labor between 24 and 34 weeks, intact membranes, cervical length between 10 and 30 mm, and negative fibronectin test were randomly allocated to nifedipine (80 mg/day) or placebo. The primary outcome was delivery within 7 days. Secondary outcomes were severe neonatal morbidity and mortality. We also followed all eligible nonrandomized women. RESULTS: We allocated 37 women to nifedipine and 36 women to placebo. In the nifedipine group, three women (8.1%) delivered within 7 days, compared with one woman (2.8%) in the placebo group (difference -5.3%; one-sided 95% confidence limit 4.5%). Median gestational age at delivery were respectively 37 + 0 (interquartile range [IQR] 34 + 6 to 38 + 5) and 38 + 2 (IQR 37 + 0 to 39 + 6) weeks (p = 0.008). In the nifedipine group, three pregnancies (8.1%) had a poor outcome; there were no poor outcomes in the placebo group. We observed similar trends in eligible nonrandomized women. CONCLUSION: In symptomatic women with preterm labor, a shortened cervix, and negative fibronectin test, placebo treatment is not inferior to tocolysis with nifedipine.

Relationship between the time interval from antenatal corticosteroid administration until preterm birth and the occurrence of respiratory morbidity.

OBJECTIVE: The purpose of this study was to assess the relationship between neonatal respiratory morbidity and the interval between antenatal corticosteroids (ACS) administration and birth. STUDY DESIGN: We performed a retrospective cohort study among women who had received ACS and delivered at <34 weeks of gestation. We categorized these women in 4 groups: ACS-to-delivery interval of 0-7, 8-14, 15-21, and 22-28 days. Multivariable logistic regression analysis assessed the association between the ACS-to-delivery interval and neonatal respiratory morbidity. RESULTS: We included 254 neonates. Eighty-two neonates (32%) were intubated. In comparison with neonates with an ACS-to-delivery interval of 0-7 days, the risk for intubation was increased in all other groups (odds ratio [OR], 2.3; 95% confidence interval [CI], 1.1-5.4; OR, 5.6; 95% CI, 1.8-18; and OR, 4.8; 95% CI, 0.71-32, not statistically significant, respectively). CONCLUSION: The effect of ACS decreases when the ACS-to-delivery interval exceeds 7 days. The first administration of ACS should be considered carefully.

Why were the results of randomized trials on the clinical utility of fetal fibronectin negative? A systematic review of their study designs.

Randomized trials on the clinical utility of fetal fibronectin in women with symptoms of preterm labor have thus far failed to demonstrate benefits. We systematically reviewed the methodology of these trials to assess if these negative results may be related to their study designs. We searched the literature for randomized trials that evaluated fibronectin testing in women with symptoms of preterm labor. Study results were evaluated and five methodological criteria were assessed: (1) randomization of discordant test results, (2) use of a fixed management protocol, (3) description of interventions in relation to the test result, (4) evaluation of a learning curve, and (5) sample size calculation in agreement with the prevalence of the test results. We detected four randomized trials that met inclusion criteria. All trials allocated women to a strategy with or without availability of fibronectin results without using a discordancy design or a fixed management protocol. One study reported the given treatment in relation to the test results. Learning curves were evaluated in one study. Two studies used transport sample size calculations. The negative results of randomized trials on fetal fibronectin may be due to particular choices in their study design.

Time to delivery after the first course of antenatal corticosteroids: a cohort study.

The optimal time interval between administration of antenatal corticosteroids and delivery is 1 to 7 days. This study evaluates the timing of the first course of antenatal corticosteroids in clinical practice. We performed a retrospective cohort study of consecutive women who had received antenatal corticosteroids and/or delivered between 24 and 34 weeks of gestation. Time between administration of corticosteroids and delivery was compared between women with different causes of anticipated preterm deliveries: symptomatic preterm labor with intact membranes; preterm premature rupture of the membranes; (pre)eclampsia; hemolysis, elevated liver enzymes, and low platelet count; intrauterine growth restriction; vaginal blood loss; and suspected fetal distress. We included 439 women of whom 348 (79%) completed the course of corticosteroids. In women with a complete course, 143 (41%) delivered within 7 days. The median interval between the course and delivery was 11 days and varied between 41 days in women with vaginal blood loss, 25 days in women with spontaneous preterm labor with intact membranes, and 8 days in women with preeclampsia ( P < 0.001). In women with spontaneous preterm labor with intact membranes and in women with vaginal blood loss, we can benefit substantially from a more accurate discrimination of women who need corticosteroids immediately and women who do not.

Cost-effectiveness of fibronectin testing in a triage in women with threatened preterm labor: alleviation of pregnancy outcome by suspending tocolysis in early labor (APOSTEL-I trial).

BACKGROUND: At present, women with threatened preterm labor before 32 weeks of gestation are, after transfer to a perinatal center, treated with tocolytics and corticosteroids. Many of these women are treated unnecessarily. Fibronectin is an accurate predictor for the occurrence of preterm birth among women with threatened preterm labor. We will assess whether triage of these women with fibronectin testing, cervical length or their combination is cost-effective. METHODS/DESIGN: We will investigate a prospective cohort of women referred to a perinatal centre for spontaneous threatened preterm labor between 24 and 34 weeks with intact membranes. All women will be tested for fibronectin and cervical length. Women with a cervical length <10 mm and women with a cervical length between 10-30 mm in combination with a positive fibronectin test will be treated with tocolytics according to local protocol. Women with a cervical length between 10-30 mm in combination with a negative fibronectin test will be randomised between treatment with nifedipine (intervention) and placebo (control) for 48 hours. Women with a cervical length > 30 mm will be managed according to local protocol. Corticosteroids may be given to all women at the discretion of the attending physician. Primary outcome measure will be delivery within 7 days. Secondary outcome measures will be neonatal morbidity and mortality, complications of tocolytics, costs and health related quality of life. The analysis will be according to the intention to treat principle. We anticipate the probability on preterm birth within 7 days in the group of women with a negative fibronectine test to be 5%. Two groups of 110 women will be needed to assure that in case of non-inferiority the difference in the proportion of preterm deliveries < 7 days will be within a prespecified boundary of 7.5% (one sided test, beta 0.2, alpha 0.05). Data obtained from women with a positive and negative fibronectin tests in both the cohort study and the trial will be integrated in a cost-effectiveness analysis that will assess economic consequences of the use of fibronectin. DISCUSSION: This study will provide evidence for the use of fibronectin testing as safe and cost-effective method in a triage for threatened preterm labor. TRIAL REGISTRATION: Nederlands Trial Register (NTR) number 1857, http://www.trialregister.nl.

The impact of fetal gender and ethnicity on the risk of spontaneous preterm delivery in women with symptoms of preterm labor.

OBJECTIVE: The objective of this study is to evaluate the relation among fetal gender, ethnicity, and preterm labor (PTL) and preterm delivery (PTD). METHODS: A secondary analysis was performed of a prospective cohort study including women with symptoms of PTL between 24 and 34 weeks. The proportion of women carrying a male or female fetus at the onset of PTL was calculated. Gestational age at delivery and risk of PTD of both fetal genders was compared and interaction of fetal gender and maternal ethnicity on the risk of PTD was evaluated. RESULTS: Of the 594 included women, 327 (55%) carried a male fetus. Median gestational age at delivery in women pregnant with a male fetus was 37 5/7 (IQR 34 4/7-39 1/7) weeks compared with 38 1/7 (IQR 36 0/7-39 5/7) weeks in women pregnant with a female fetus (p = 0.032). The risk of PTD did not differ significantly. In Caucasians, we did find an increased risk of PTD before 37 weeks in women pregnant with a male fetus (OR 1.9 (95% CI 1.2-3.0)). CONCLUSIONS: The majority of women with PTL are pregnant with a male fetus and these women deliver slightly earlier. Race seems to affect this disparity.

Comparison of the Actim Partus test and the fetal fibronectin test in the prediction of spontaneous preterm birth in symptomatic women undergoing cervical length measurement.

OBJECTIVE: To compare the accuracy of the Actim Partus test and fetal fibronectin (fFN) test in the prediction of spontaneous preterm delivery within seven days in symptomatic women undergoing cervical length measurement. STUDY DESIGN: We performed a post-hoc analysis on frozen samples of a nationwide cohort study in all 10 perinatal centres in the Netherlands. We selected samples from women with signs of preterm labour between 24 and 34 weeks of gestational age and a cervical length below 30mm. Delivery within seven days after initial assessment was the primary endpoint. We calculated sensitivity, specificity, and positive and negative predictive values for the combination of both the Actim Partus test and fFN test with cervical length. A test was considered positive in case of a cervical length between 15 and 30mm with a positive Actim Partus or fFN test, and a cervical length below 15mm regardless the test result. RESULTS: In total, samples of 350 women were tested, of whom 69 (20%) delivered within seven days. Eighty-four women had a positive Actim Partus test and 162 women a positive fFN test, of whom 54 (64%) and 63 (39%) delivered within seven days, respectively. Ninety-seven women had a cervical length below 15mm, of whom 50 (52%) delivered within seven days. Sensitivity, specificity, positive and negative predictive values of combining cervical length with the Actim Partus test or the fFN test were 91%, 75%, 47% and 97%, and 96%, 58%, 36% and 98%, respectively. CONCLUSION: According to this post-hoc study, in combination with cervical length, the Actim Partus test could be used as an alternative for the fFN test to identify women who will not deliver within seven days after presentation. Further evidence should be collected in a prospective comparative study.

Prescribing patterns of antenatal corticosteroids in women with threatened preterm labor.

OBJECTIVE: To assess the impact of cervical length (CL) measurement and fetal fibronectin testing (fFN) on the clinicians' decision to prescribe antenatal corticosteroids (ACS) to women with symptoms of preterm labor. STUDY DESIGN: This is a secondary analysis of a prospective cohort study including women with symptoms of preterm labor and intact membranes between 24 and 34 weeks' gestation. We compared the proportion prescribed and completed ACS courses, preterm delivery within seven days and median intervals from ACS to delivery in four groups: group 1 CL<10 mm, group 2 CL 10-30 mm and positive fFN, group 3 CL 10-30 mm and negative fFN, group 4 CL>30 mm. RESULTS: ACS were prescribed to 63/65 (97%) women in group 1, 176/192 (91%) in group 2, 111/172 women (65%) in group 3 and 55/242 (23%) in group 4. In group 1, 42 (65%) women delivered within seven days, compared to 34 (18%) in group 2, 6 (3%) in group 3 and 3 (1%) in group 4. Median intervals between ACS and delivery were 6 days (IQR 3-61 days), 44 days (IQR 17-69 days), 53 days (IQR 37-77 days) and 66 days (IQR 43-78 days) in group 1, 2, 3 and 4 respectively. CONCLUSION: ACS were prescribed frequently to women with a CL of 10-30 mm and a negative fFN test or a CL>30 mm. There is room for improvement in the prescription of ACS in these low risk women.

Risk factors for preterm delivery: do they add to fetal fibronectin testing and cervical length measurement in the prediction of preterm delivery in symptomatic women?

OBJECTIVE: To assess whether patient characteristics add to the fetal fibronectin test and cervical length measurement in the prediction of preterm delivery in symptomatic women. STUDY DESIGN: A nationwide prospective cohort study was conducted in all ten perinatal centres in the Netherlands. Women with symptoms of preterm labour between 24 and 34 weeks gestation with intact membranes were invited. In all women qualitative fibronectin testing (0.050 µg/mL cut-off) and cervical length measurement were performed. Only singleton pregnancies were included in this analysis. Logistic regression was used to construct two multivariable models to predict spontaneously delivery within 7 days: a model including cervical length and fetal fibronectin as predictors, and an extended model including all potential predictors. The models were internally validated using bootstrapping techniques. Predictive performances were assessed as the area under the receiver operator characteristic curve (AUC) and calibration plots. We compared the models' capability to identify women with a low risk to deliver within 7 days. A risk less than 5%, corresponding to the risk for women with a cervical length of at least 25 mm, was considered as low risk. RESULTS: Seventy-three of 600 included women (12%) had delivered spontaneously within 7 days. The extended model included maternal age, parity, previous preterm delivery, vaginal bleeding, C-reactive protein, cervical length, dilatation and fibronectin status. Both models had high discriminative performances (AUC of 0.92 (95% CI 0.88-0.95) and 0.95 (95% CI 0.92-0.97) respectively). Compared to the model with fibronectin and cervical length, our extended model reclassified 38 women (6%) from low risk to high risk and 21 women (4%) from high risk to low risk. Preterm delivery within 7 days occurred once in both the reclassification groups. CONCLUSION: In women with symptoms of preterm labour before 34 weeks gestation, a model that integrates maternal characteristics, clinical signs and laboratory tests, did not predict delivery within 7 days better than a model with only fibronectin and cervical length.

Predictive value of cervical length measurement and fibronectin testing in threatened preterm labor.

OBJECTIVE: To estimate the performance of combining cervical length measurement with fetal fibronectin testing in predicting delivery in women with symptoms of preterm labor. METHODS: We conducted a prospective nationwide cohort study in all 10 perinatal centers in The Netherlands. Women with symptoms of preterm labor between 24 and 34 weeks of gestation with intact membranes were included. In all women, qualitative fibronectin testing (0.050-microgram/mL cutoff) and cervical length measurement were performed. Logistic regression was used to predict spontaneous preterm delivery within 7 days after testing. A risk less than 5%, corresponding to the risk for women with a cervical length of at least 25 mm, was considered as low risk. RESULTS: Between December 2009 and August 2012, 714 women were enrolled. Fibronectin results and cervical length were available for 665 women, of whom 80 (12%) delivered within 7 days. Women with a cervical length of at least 30 mm or with a cervical length between 15 and 30 mm with a negative fibronectin result were at low risk (less than 5%) of spontaneous delivery within 7 days. Fibronectin testing in case of a cervical length between 15 and 30 mm additionally classified 103 women (15% of the cohort) as low risk and 36 women (5% of the cohort) as high risk. CONCLUSION: Cervical length measurement, combined with fetal fibronectin testing in case of a cervical length between 15 and 30 mm, improves identification of women with a low risk to deliver spontaneously within 7 days. LEVEL OF EVIDENCE: II.

[Predicating imminent preterm labour based on a determination of foetal fibronectin in a vaginal smear]. / Voorspellen van dreigende vroeggeboorte door middel van bepaling van foetaal fibronectine in vaginaal vocht.

OBJECTIVE: To determine the prognostic value of foetal fibronectin and cervical length for predicting imminent preterm labour among Dutch women, who in the Netherlands normally undergo a digital examination of the cervix prior to referral to a hospital or university medical centre. DESIGN: Prospective observational cohort study. METHODS: Pregnant women with symptoms of preterm labour and a gestational age between 24 and 34 weeks were included. A fibronectin smear was taken from them and the cervical length was measured. Primary outcome was delivery within 7 days after inclusion. Sensitivity, specificity and a receiver-operating characteristics (ROC) curve were calculated. RESULTS: 13 (12%) of the 108 included patients delivered spontaneously within 7 days after inclusion. The fibronectin test had a sensitivity of 92% and specificity of 60%. The positive and negative predictive values were 27% and 98% respectively. For women who had undergone a digital examination prior to testing, the predictive value was slightly less but the difference was not significant. Although measurement of the cervical length scarcely had a predictive value, none of the patients with a cervical length above 35 mm delivered within 7 days. CONCLUSION: In women with an imminent preterm labour, a negative fibronectin test virtually ruled out delivery within 7 days. The fibronectin test can therefore also be used in the Dutch situation. In women with a cervix length greater than 35 mm, the chance of a preterm labour within 7 days is very small and a fibronectin test does not need to be performed in their case.

Fetal complications after placement of an intrauterine pressure catheter: a report of two cases and review of the literature.

BACKGROUND: Uterine contractions during labor can be monitored by external tocodynamometry or by the use of an intrauterine pressure catheter (IUPC). Since an IUPC measures the frequency of contractions as well as their strength and duration, it is thought to be more accurate than external tocodynamometry. However, limited evidence on this subject suggests that IUPC may not improve maternal or perinatal outcomes. Moreover, the use of IUPC may cause fetal complications. CASES: We describe the placement of an IUPC during induction of labor with oxytocin in two cases, one presenting with a singleton pregnancy and the other a twin pregnancy. After introduction of the IUPC, both cases were complicated by blood loss and signs of fetal distress on cardiotocography. An emergency cesarean section was performed in both cases. In the first case, extramembranous placement of the IUPC was observed, whereas in the second case, the IUPC had lacerated an arteriovenous anastomosis in the membranes, resulting in perinatal death. CONCLUSION: Placement of an intrauterine pressure catheter instead of external tocodynamometry has a small risk for serious fetal complications.