Maternal and pathological pregnancy characteristics in customised birthweight centiles and identification of at-risk small-for-gestational-age infants: a retrospective cohort study

Authors

  • NH Anderson,

    1. Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
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  • LC Sadler,

    1. Department of Obstetrics and Gynaecology, National Women’s Health, Auckland City Hospital, Auckland, New Zealand
    2. Department of Epidemiology and Biostatistics, School of Population Health, Faculty of Medical and Health Sciences, University of Auckland, Auckland New Zealand
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  • AW Stewart,

    1. Department of Epidemiology and Biostatistics, School of Population Health, Faculty of Medical and Health Sciences, University of Auckland, Auckland New Zealand
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  • LME McCowan

    1. Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
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Dr NH Anderson, Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Email ngaire.anderson@auckland.ac.nz

Abstract

Please cite this paper as: Anderson N, Sadler L, Stewart A, McCowan LE. Maternal and pathological pregnancy characteristics in customised birthweight centiles and identification of at-risk small-for-gestational-age infants: a retrospective cohort study. BJOG 2012;119:848–856.

Objective  To regenerate coefficients for the New Zealand customised birthweight centile calculator using an updated birth cohort, and compare the identification of at-risk small-for-gestational-age (SGA) infants between full customisation (including maternal characteristics) and an ultrasound-based fetal weight and infant gender partial customisation.

Design  Retrospective cohort study of prospectively collected maternity data.

Setting  National Women’s Health Auckland, New Zealand.

Population  Singleton pregnancies in the period 2006–2009; n = 24 176.

Methods  Multiple linear regression analysis was performed for full customisation (adjusted for gestation, infant gender, maternal characteristics and pathological variables) and ultrasound-and-gender customisation (adjusted for gestation and infant gender).

Main outcome measures  Risks of SGA-related perinatal death were compared between models.

Results  Changes occurred in some ethnicity coefficients, including Chinese (−135 g), Tongan (−101 g) and Samoan (−89 g), and ten ethnicities were added. Overall, full customisation identified SGA infants with higher odds of perinatal death (OR 5.6, 95% CI 3.6–8.7) than infants classed as SGA by ultrasound-and-gender customisation (OR 2.1, 95% CI 1.4–3.3) (= 0.02). In subgroup analyses, infants classed as SGA by full but not ultrasound-and-gender customisation (n = 888, 3.4%) had an increased risk of perinatal death (RR 4.7, 95% CI 2.7–7.9); however, those identified as SGA by ultrasound-and-gender customisation alone were not at an increased risk (n = 676, 2.6%, RR 1.1, 95% CI 0.4–3.6). The population attributable risk (PAR) of SGA-related perinatal death was higher for full (49.8%) than for ultrasound-and-gender (43.0%) customisation.

Conclusions  Updating the New Zealand customised birthweight centile calculator resulted in revised coefficients that better reflect a contemporary birth cohort. Inclusion of maternal characteristics in a birthweight customisation model increases the detection of SGA infants at risk of perinatal death.

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