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DSECT/DSEN Monthly Seminar Series - Nov 25 2021 - Immortal time bias in pregnancy studies

“Immortal time bias in pregnancy studies”


Presented by

Dr. Ugochinyere Vivian Ukah

Postdoctoral Fellow, McGill University 

Thursday, November 25, 2021 3- 4pm EST



Time-related biases, such as immortal time bias, often occur in observational studies. However, the occurrence and prevalence of immortal time bias in pregnancy studies is not well understood. In this presentation, I demonstrate how immortal time bias can occur, particularly in pregnancy studies. I also describe the frequency of immortal bias in a systematic review of observational perinatal pharmacoepidemiological studies. Twelve out of 21 studies (57.1%) had immortal time bias, suggesting the need for more appropriate study design and analyses to prevent immortal time bias in pregnancy studies.  

Learning Objectives:  

  1. To understand what immortal time bias is and how they can affect study results
  2. To be able to identify studies with potential immortal time bias.  

Supporting Resources 

  • Suissa S, Dell’Aniello S. Time‐related biases in pharmacoepidemiology. Pharmacoepidemiol Drug Saf. 2020;29(9):1101-1110. doi:10.1002/pds.5083
  • Platt RW, Hutcheon JA, Suissa S. Immortal Time Bias in Epidemiology. Curr Epidemiol Rep. 2019;6(1):23-27. doi:10.1007/s40471-019-0180-5
  • Hutcheon JA, Kuret V, Joseph KS, Sabr Y, Lim K. Immortal Time Bias in the Study of Stillbirth Risk Factors: The Example of Gestational Diabetes.
  • Hernán MA, Sauer BC, Hernández-Díaz S, Platt R, Shrier I. Specifying a target trial prevents immortal time bias and other self-inflicted injuries in observational analyses. J Clin Epidemiol. 2016;79(Journal Article):70-75. doi:10.1016/j.jclinepi.2016.04.014

Link to recording