International journal of obstetric anesthesia
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Int J Obstet Anesth · Dec 2024
On causal inferences from retrospective and observational studies and their implications for neuraxial labor analgesia: the CHRISTMAS* study.
Observational studies should not be used to infer causation as they are prone to confounding factors, selection bias, and reverse causality. Many observational studies of labor analgesia treated epidurals as an independent exposure and concluded that "epidurals" cause dystocia, despite multiple randomized controlled trials showing no effect. We highlight this problem using reductio ad absurdum. We explore whether people request reading glasses when their progressively increasing focal length equals or exceeds their fixed arm length. ⋯ Even if this observational study had demonstrated a strong correlation between age at request for reading glasses and arm length, it would have been absurd to conclude that spectacles somehow cause our arms to shrink. Similarly, women in obstructed labor with a narrow pelvis are more likely to request neuraxial labor analgesia, but "epidurals" do not make their pelvis shrink. Making far-reaching causal inferences based on retrospective or observational data is very shortsighted.