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Erratum to: Pessaries in multiple pregnancy as a prevention of preterm birth: the ProTwin Trial

BMC Pregnancy and Childbirth volume 12, Article number: 37 (2012) Cite this article

The initial sample size calculation in our protocol [1] was based on the expected proportion of ‘bad neonatal outcome’ in the intervention group (3.9%) and control group (7.2%) and accounts for the fact that the outcomes in children from multiple pregnancies are non-independent using an intra class correlation of 0.6. As the intervention is performed on the mother, analysis should be done on the maternal level. This adjustment was made during recruitment and approved by the medical ethics committee. The sample size is calculated based on the primary outcome 'bad neonatal outcome'. In the control group, 'bad neonatal outcome' is expected in 7.2% of the children 1.8 % * 77 % + 5.4 % * 35 % + 7.2 % * 12 % + 35.6 % * 8 % + 50 % * . 5 % = 7.2 % . In this calculation, the first rate represents the probability that a patient delivers at that gestational age, whereas the second rate represents the probability of 'bad neonatal outcome' at that particular gestational age. In case of treatment, 'bad neonatal outcome' is then expected in 3.9% of the children 0.9 % * 77 % + 2.7 % * 35 % + 3.6 % * 12 % + 17.8 % * 8 % + 75 % * . 5 % = 3.9 % . On the mother level this corresponds to an expected ‘bad neonatal outcome’ in at least one of two children of 12.4% in the control group and 6.7% in case of treatment. Using a two-sided test with an alpha of 0.05 and a power of 0.80 we need 400 women in the control group and 400 in the intervention group.

* Medical Ethics Committee, Academic Medical Centre, Amsterdam, the Netherlands (ref. No. MEC 09/107).

References

  1. 1.

    Hegeman MA, Bekedam DJ, Bloemenkamp KWM, Dimitri AK Papatsonis, van der Post NM, Joris AM, et al: Pessaries in multiple pregnancy as a prevention of preterm birth: the ProTwin Trial. BMC Pregnancy Childbirth. 2009, 9: 44-10.1186/1471-2393-9-44.

Pre-publication history

  1. The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2393/12/37/prepub

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Affiliations

  1. Department of Obstetrics and Gynaecology, Onze Lieve Vrouwe Gasthuis Amsterdam, Amsterdam, The Netherlands
    • Sophie MS Liem
    • , Dick J Bekedam
    •  & Maud A Hegeman
  2. Department of Obstetrics and Gynaecology, Leiden University Medical Center, Leiden, The Netherlands
    • Kitty WM Bloemenkamp
  3. Department of Obstetrics and Gynaecology, University Medical Centre, Utrecht, The Netherlands
    • Anneke Kwee
    •  & Hein W Bruinse
  4. Department of Obstetrics and Gynaecology, AMPHIA hospital, Breda, The Netherlands
    • Dimitri NM Papatsonis
  5. Department of Obstetrics and Gynaecology, Academic Medical Centre Amsterdam, Amsterdam, The Netherlands
    • Sophie MS Liem
    • , Joris AM van der Post
    • , Arianne C Lim
    •  & Ben Willem J Mol
  6. Department of Obstetrics and Gynaecology, Academic Hospital Maastricht, Maastricht, The Netherlands
    • Hubertina CJ Scheepers
    •  & Christine Willekes
  7. Department of Obstetrics and Gynaecology, Erasmus Medical Center Rotterdam, Rotterdam, The Netherlands
    • Johannes J Duvekot
  8. Department of Obstetrics and Gynaecology, University Medical Center St Radboud Nijmegen, Nijmegen, The Netherlands
    • Marc Spaanderman
  9. Department of Obstetrics and Gynaecology, Máxima Medical Center Veldhoven, Veldhoven, The Netherlands
    • Martina Porath
  10. Department of Obstetrics and Gynaecology, Isala Hospital, Zwolle, The Netherlands
    • Jim van Eyck
  11. Department of Obstetrics and Gynaecology, VU Medical Center Amsterdam, Amsterdam, The Netherlands
    • Monique C Haak
  12. Department of Obstetrics and Gynaecology, University Medical Center Groningen, Groningen, The Netherlands
    • Marielle G van Pampus
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Corresponding author

Correspondence to Sophie MS Liem.

Additional information

The online version of the original article can be found at 10.1186/1471-2393-9-44

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Liem, S.M., Bekedam, D.J., Bloemenkamp, K.W. et al. Erratum to: Pessaries in multiple pregnancy as a prevention of preterm birth: the ProTwin Trial. BMC Pregnancy Childbirth 12, 37 (2012). https://doi.org/10.1186/1471-2393-12-37

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BMC Pregnancy and Childbirth

ISSN: 1471-2393

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