Background: The diagnosis of preterm labour is challenging. False-positive diagnoses are common and result in unnecessary, potentially harmful treatments (e.g. tocolytics, antenatal corticosteroids and magnesium sulphate) and costly hospital admissions. Measurement of fetal fibronectin in vaginal fluid is a biochemical test that can indicate impending preterm birth.
Objectives: To develop an externally validated prognostic model using quantitative fetal fibronectin concentration, in combination with clinical risk factors, for the prediction of spontaneous preterm birth and to assess its cost-effectiveness.
Design: The study comprised (1) a qualitative study to establish the decisional needs of pregnant women and their caregivers, (2) an individual participant data meta-analysis of existing studies to develop a prognostic model for spontaneous preterm birth within 7 days in women with symptoms of preterm labour based on quantitative fetal fibronectin and clinical risk factors, (3) external validation of the prognostic model in a prospective cohort study across 26 UK centres, (4) a model-based economic evaluation comparing the prognostic model with qualitative fetal fibronectin, and quantitative fetal fibronectin with cervical length measurement, in terms of cost per QALY gained and (5) a qualitative assessment of the acceptability of quantitative fetal fibronectin.
Data sources/setting: The model was developed using data from five European prospective cohort studies of quantitative fetal fibronectin. The UK prospective cohort study was carried out across 26 UK centres.
Participants: Pregnant women at 22+0-34+6 weeks' gestation with signs and symptoms of preterm labour.
Health technology being assessed: Quantitative fetal fibronectin.
Main outcome measures: Spontaneous preterm birth within 7 days.
Results: The individual participant data meta-analysis included 1783 women and 139 events of spontaneous preterm birth within 7 days (event rate 7.8%). The prognostic model that was developed included quantitative fetal fibronectin, smoking, ethnicity, nulliparity and multiple pregnancy. The model was externally validated in a cohort of 2837 women, with 83 events of spontaneous preterm birth within 7 days (event rate 2.93%), an area under the curve of 0.89 (95% confidence interval 0.84 to 0.93), a calibration slope of 1.22 and a Nagelkerke R2 of 0.34. The economic analysis found that the prognostic model was cost-effective compared with using qualitative fetal fibronectin at a threshold for hospital admission and treatment of ≥ 2% risk of preterm birth within 7 days.
Limitations: The outcome proportion (spontaneous preterm birth within 7 days of test) was 2.9% in the validation study. This is in line with other studies, but having slightly fewer than 100 events is a limitation in model validation.
Conclusions: A prognostic model that included quantitative fetal fibronectin and clinical risk factors showed excellent performance in the prediction of spontaneous preterm birth within 7 days of test, was cost-effective and can be used to inform a decision support tool to help guide management decisions for women with threatened preterm labour.
Future work: The prognostic model will be embedded in electronic maternity records and a mobile telephone application, enabling ongoing data collection for further refinement and validation of the model.
Study registration: This study is registered as PROSPERO CRD42015027590 and Current Controlled Trials ISRCTN41598423.
Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 52. See the NIHR Journals Library website for further project information.
Keywords: FETAL FIBRONECTIN; INDIVIDUAL PARTICIPANT DATA LEVEL META-ANALYSIS; NEONATAL; PARTURITION; PREGNANCY; PRETERM LABOUR; PROGNOSTIC MODEL.
Identifying which women with symptoms of labour will give birth early is challenging, so many women unnecessarily receive therapies aimed at preventing complications in preterm birth. A test called quantitative fetal fibronectin, which uses vaginal swab samples, may help to improve the diagnosis of preterm labour. Fetal fibronectin is a protein that is released from the fetal membranes that surround the developing baby in the womb. The lower the concentration of fetal fibronectin, the less likely the occurrence of preterm birth. Our aim was to see if quantitative fetal fibronectin, in combination with some features of pregnancy (e.g. previous pregnancy history and twin pregnancy), can accurately predict preterm birth in women who have symptoms of preterm labour. We asked women, their partners, doctors and midwives what information would be most useful to them, and how this should be presented. We then analysed previous research data; we used quantitative fetal fibronectin and clinical risk factors together to predict the chance of preterm birth. We explored which features could predict preterm birth most effectively while still being good value to the NHS. To ensure that this risk predictor worked in UK populations, we undertook a research study across 26 UK hospitals. Women who had symptoms of preterm labour were invited to participate. We collected information from these women (approximately 3000 women), including quantitative fetal fibronectin results. We found that a risk predictor comprising quantitative fetal fibronectin and four other features performed best at predicting whether or not preterm birth will occur within the next week for women with symptoms of preterm labour, and that this had potential to be clinically useful and cost-effective. The quantitative fetal fibronectin testing process was acceptable to women, and clinicians found the risk predictor useful. We used our findings to develop a risk calculator to help women and clinicians assess how likely preterm birth is, and decide whether or not to start treatment.