Prediction of spontaneous preterm delivery in women with threatened preterm labour: a prospective cohort study of multiple proteins in maternal serum

Authors

  • P Tsiartas,

    1. Department of Obstetrics and Gynaecology, Papageorgiou University Hospital, Thessaloniki, Greece
    2. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
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  • R-M Holst,

    1. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
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  • U-B Wennerholm,

    1. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
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  • H Hagberg,

    1. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
    2. Institute of Reproductive and Developmental Biology, Hammersmith Campus, Imperial College, London, UK
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  • DM Hougaard,

    1. Department of Clinical Biochemistry and Immunology, Statens Serum Institute, Copenhagen, Denmark
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  • K Skogstrand,

    1. Department of Clinical Biochemistry and Immunology, Statens Serum Institute, Copenhagen, Denmark
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  • BD Pearce,

    1. Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA, USA
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  • P Thorsen,

    1. Department of Obstetrics and Gynaecology, Lillebaelt Hospital, Kolding, Denmark
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  • M Kacerovsky,

    1. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
    2. Department of Obstetrics and Gynaecology, Charles University in Prague, Faculty of Medicine Hradec Kralove, University Hospital Hradec Kralove, Hradec Kralove, Czech Republic
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  • B Jacobsson

    1. Department of Obstetrics and Gynaecology, Institute for Clinical Sciences, Sahlgrenska Academy, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
    2. Institute of Public Health, Oslo, Norway
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Authors’ Reply

Sir,

First, we would like to thank Dr Sabour1 for his interest in our paper.2 He has raised important questions regarding the data analyses, which we appreciate taking the opportunity to clarify.

We agree, and have pointed out in our Conclusions, that the predictive model needs to be validated in a new cohort in order to confirm its predictive ability. When we performed the analyses, we decided not to divide our data set into two parts to develop the model in one half and test it in the other. This division would have resulted in a substantial reduction of the predictive power of this study, with its limited number of patients. Our results must thus be replicated in another cohort.

The prediction models in the paper were created based on a stepwise logistic regression.2 The calculations resulted in several models with almost similar predictive capacity, of which we have chosen to present the best. A bootstrapping approach would have led to many of these models being found to be almost similar, which might have led to misleading results if presented for the single model chosen, or for all possible models. Therefore, we chose not to use bootstrapping methodology in this study.

We agree that sensitivity, specificity, positive and negative predictive values, positive likelihood ratio (LR+), negative likelihood ratio (LR) and odds ratio are among the tests that can be used to evaluate the validity of a test in relation to a gold standard. As we have stated in the Discussion, the gold standard in our study is cervical length measurement by transvaginal ultrasound.2,3 We believe that we have addressed the issue that concerns Dr Sabour in the comparison between our final model, the best model from just the biomarkers, and the gold standard in Table 4.2 We also believe that we have addressed the LR issue in Table 3.3

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