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The use of customised versus population-based birthweight standards in predicting perinatal mortality

  1. X Zhang,
  2. RW Platt,
  3. S Cnattingius,
  4. KS Joseph,
  5. MS Kramer*

Article first published online: 9 MAR 2007

DOI: 10.1111/j.1471-0528.2007.01273.x

Issue

BJOG: An International Journal of Obstetrics & Gynaecology

BJOG: An International Journal of Obstetrics & Gynaecology

Volume 114, Issue 4, pages 474–477, April 2007

Additional Information

How to Cite

Zhang, X., Platt, R., Cnattingius, S., Joseph, K. and Kramer, M. (2007), The use of customised versus population-based birthweight standards in predicting perinatal mortality. BJOG: An International Journal of Obstetrics & Gynaecology, 114: 474–477. doi: 10.1111/j.1471-0528.2007.01273.x

Author Information

  1. a Department of Pediatrics and b Department of Epidemiology and Biostatistics, McGill University Faculty of Medicine, Montreal, Quebec, Canada c Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden d Department of Obstetrics & Gynaecology, Dalhousie University and the IWK Health Centre, Halifax, Nova Scotia, Canada

*Dr MS Kramer, The Montreal Children’s Hospital, 2300 Tupper Street (Les Tourelles), Montreal, Quebec, Canada H3H 1P3. Email michael.kramer@mcgill.ca

Publication History

  1. Issue published online: 9 MAR 2007
  2. Article first published online: 9 MAR 2007
  3. Accepted 31 December 2006.

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Keywords:

  • Fetal growth;
  • intrauterine growth restriction;
  • perinatal mortality;
  • small for gestational age;
  • stillbirth

Objective  The objective of this study was to critically examine potential artifacts and biases underlying the use of ‘customised’ standards of birthweight for gestational age (GA).

Design  Population-based cohort study.

Setting  Sweden.

Population  A total of 782 303 singletons ≥28 weeks of gestation born in 1992–2001 to Nordic mothers with complete data on birthweight; GA; and maternal age, parity, height, and pre-pregnancy weight.

Methods  We compared perinatal mortality in four groups of infants based on the following classification of small for gestational age (SGA): non-SGA based on either population-based or customised standards (the reference group), SGA based on the population-based standard only, SGA based on the customised standard only, and SGA according to both standards. We used graphical methods to compare GA-specific birthweight cutoffs for SGA using the two standards and also used logistic regression to control for differences in GA and maternal pre-pregnancy body mass index (BMI) in the four groups.

Main outcome measures  Perinatal mortality, including stillbirth and neonatal death.

Results  Customisation led to a large artifactual increase in the proportion of SGA infants born preterm. Adjustment for differences in GA and maternal BMI markedly reduced the excess risk among infants classified as SGA by customised standards only.

Conclusion  The large increase in perinatal mortality risk among infants classified as SGA based on customised standards is largely an artifact due to inclusion of more preterm births.

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