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Routine induction in late-term pregnancies: follow-up of a Danish induction of labour paradigm
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  • Published on:
    Response to Pedersen's comment to our paper "Routine induction in late-term pregnancies: follow-up of a Danish induction of labour paradigm
    • Eva Rydahl, Associate Professor, Ph.d. Department of Midwifery, University College Copenhagen

    We appreciate the interest that Dr. Pedersen has shown in our paper, but he has apparently misunderstood some aspects of our analysis. In the analysis of the stillbirth data, we first described the dependence of log (rate) on calendar year by a straight line. Next, we allowed the slope to change from 2011 onwards (a so-called linear spline with a knot at 2011). This did not improve the fit significantly. This is the analysis reported in our paper. Besides we also tried to see if a change in intercept from 2011 onwards would lead to a significantly better fit. This was not the case. This latter model is the one that Dr. Pedersen considers, but this was not the one presented in our paper.

    We are also concerned about Dr. Pedersen’s suggestion that we have been unresponsive to his questions. We can document at least 11 email correspondences and two face to face meetings with Dr. Pedersen to accommodate Dr. Pedersen’s wish for more information and discussion of our analyses. These mails and meetings have also included the Lead Professor of Dr. Pedersen’s department and a Professor in Biostatistics from Aarhus University. The Professor in Biostatistics has confirmed to all included in the meetings and in the additional emails that our analysis as well as our conclusions in the paper were valid.

    Eva Rydahl, Eugene Declercq, Mette Juhl, Rikke Damkjær Maimburg

    Conflict of Interest:
    None declared.
  • Published on:
    Issues with the statistical models, Rydahl et al, BMJ Open, 2019
    • Lars H Pedersen, Professor, Consultant Obstetrician Aarhus University, Depts. Clinical Medicine & Biomedicine. Aarhus University Hospital, Obstetrics & Gynecology, Aarhus, Denmark

    I would like to point to potential problems with the statistical models of Rydahl et al:

    For stillbirths, they fit a Poisson model log(rate) = a + b*year + c*dummy(2011) (dummy(2011) is 0 before and 1 after the change in guideline) [personal communication], a model that obviously allow for no change in the slope before and after 2011. This is problematic because the actual data indicate that the stillbirth rate decreases up to 2011 and increases after 2011 (acknowledged by Rydahl et al (p. 6) and suggested by a recent paper based on similar data [1]). Because the model is underfitted, the findings may be unreliable (false negative).
    A basic simulation illustrates the problem: the underlying hypothesis is that the stillbirth rate reflects the induction rate (i.e. the number of ongoing pregnancies) and that stillbirths consequently reflects the Figure 2A changes over time. If the risk of stillbirth is proportional to the number of ongoing pregnancies, one simple simulated data could be per year n=16, 16, 14, 13, 12, 12, 11, 11, 11, 10, 11, 8, 5, 6, 6, 7, 8 from 2000 to 2016. The model applied by Rydahl et al would be unable to detect the build-in change in this simulated data. In fact, as expected, only some models would be able to detect the change: for example, in a quasi-Poisson model with interaction, the before-after dummy is statistically significant (p=0.045). Interestingly, if this model is applied to the published data, the dummy(2011) is statistically...

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    Conflict of Interest:

    The last author and I are employed at the same department, and I participate in a working group under the National Board of Health with the first author. They have been informed several times about my concerns by e-mails and at meetings. Because the discussions have led to no common ground, I feel compelled to comment in public.
  • Published on:
    Response to Lidegaard et al.'s comment to our paper "Routine induction in late-term pregnancies: follow-up of a Danish induction of labour paradigm
    • Rikke D Maimburg, Associate Professor Department of Clinical Medicine, Aarhus University Hospital

    We appreciate the interest in our recently published paper on induction of labour and the very quick response by Lidegaard et al., giving us the opportunity to elaborate on the assumptions and questions raised.

    Our comments are listed below:
    Lidegaard et al. state that our study in BMJ Open is “yet an attempt to question a more offensive post-term induction practice” perhaps with a reference to a peer reviewed systematic review published earlier this year. First, we would like to point towards a professional way of communicating. Everyone, both the women and the professionals will benefit if we agree on being professional in our way of discussing research and clinical practice. Having said so, it is correct, that two of the authors of our BMJ Open publication have published a systematic review comparing routine induction of labour at 41+0/6 gestational weeks to 42+0/6 gestational weeks [1]. The systematic review revealed adverse maternal outcomes associated with routine induction of labour at 41+0/6 gestational weeks as well as both benefits and harms for the newborns by each regime. In the current paper, we did not study any offensive post-term labour induction practice as suggested by Lidegaard et al., but the practice of treating otherwise healthy pregnant women at 41+3/5 gestational weeks, where they are within the normal range of pregnancy and not yet post-term.
    We do not agree on the simple causal argumentation suggested by Lidegaard et al. based...

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    Conflict of Interest:
    None declared.
  • Published on:
    Record low stillbirth rates in Denmark
    • Øjvind Lidegaard, Professor in Obstetrics & GynaecologyMD, DMSci Rigshospitalet, University of Copenhagen
    • Other Contributors:
      • Niels Uldbjerg, Professor in Obstetrics
      • Morten Hedegaard, MD, specialist in Obstetrics and Gynaecology

    Thanks to Rydahl et al. for yet an attempt to question a more offensive post-term induction practice to have a main responsibility for the impressing reduction in stillbirths in Denmark (1). The more offensive induction practice was gradually implemented in Denmark through this century but accelerated by the National recommendation in 2010-2011 to induce post-term women so to ensure delivery before 42 gestational weeks (GW).
    The following comments assume that the data presented by Rydahl et al. are correct, we are currently looking at the same issue and the same data.
    First what we agree on:
    • There has from 2000 to 2012 been a substantial decrease in stillbirths in Denmark among women pregnant beyond 41+3 GW. The reduction was from 2.6 to <0.5 stillbirths per 1000 delivered, a reduction of at least 80%. Shouldn’t we start by congratulating each other for this impressing National achievement.
    • During the same period has the proportion of induced deliveries increased for women going beyond 41+3 GW from 25% to around 65%.
    • Despite this dramatic change in induction practice, both Caesarean section rates, low Apgar scores, and birth augmentation have been almost stable.
    • The proportion of instrumental births has decreased during the same period.

    It is of course an important issue what caused the dramatic decrease in stillbirths over the last two decades in Denmark. We have previously published evidence arguing that the more offe...

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    Conflict of Interest:
    None declared.