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On the pitfalls of adjusting for gestational age at birth

Allen J Wilcox1, Clarice R Weinberg, Olga Basso

  • 1Epidemiology Branch (MD A3-05), National Institute of Environmental Health Sciences, P.O. Box 12233, Durham, NC 27709, USA. wilcox@niehs.nih.gov

American Journal of Epidemiology
|September 28, 2011
PubMed

Insights

Adjusting for gestational age in preterm birth studies can create bias, potentially reversing findings. This highlights the need to reconsider its use in perinatal research for accurate causal inference.

Area of Science:

  • Perinatal epidemiology
  • Maternal-fetal medicine
  • Biostatistics

Background:

  • Preterm delivery is a major cause of infant morbidity and mortality.
  • Underlying pathological factors causing preterm birth are not fully understood.
  • These factors can confound the association between early delivery and neonatal outcomes.

Purpose of the Study:

  • To investigate the impact of adjusting for gestational age in studies of preterm birth.
  • To explore the potential for bias, including outcome reversal, due to gestational age adjustment.
  • To clarify the role of gestational age as a collider in perinatal research.

Main Methods:

  • Review of theoretical concepts of colliders in causal inference.
  • Presentation of simulation studies to quantify bias from gestational age adjustment.
  • Analysis of confounding in the association between risk factors and neonatal outcomes.

Main Results:

  • Adjustment for gestational age can introduce significant bias when estimating direct effects.
  • Under certain conditions, this bias can lead to a complete reversal of exposure-outcome associations.
  • Gestational age is identified as a collider, complicating causal inference.

Conclusions:

  • Adjusting for gestational age is generally not justified for causal inference in perinatal research.
  • Failure to appreciate gestational age as a collider can lead to erroneous conclusions.
  • Revising analytical strategies is crucial for accurate understanding of preterm birth impacts.

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