On causal inferences from retrospective and observational studies and their implications for neuraxial labor analgesia: The CHRISTMAS study

• Published in: International journal of obstetric anesthesia 2024-12, Vol.61, p.104307, Article 104307
• Main Authors: Ginosar, Yehuda, Sandman, Or, Tevet, Aharon, Boret, Malka, Greenberger, Riki, Boim, Zipora, Naffar, Ibrahim, Harpenas, Esty, Pe’er, Jacob, Bdolah-Abram, Tali, Calderon-Margalit, Ronit, Ben-Eli, Hadas
• Format: Article
• Language: English
• ISSN: 0959-289X; 1532-3374; 1532-3374
• DOI: 10.1016/j.ijoa.2024.104307

•Observational studies can identify associations between exposures and outcomes, but should not be used to infer causation. (124 characters with spaces)•Cephalopelvic disproportion causes long painful labor with more epidurals, but epidurals do not make the pelvis constrict. (125 characters with spaces)•Even if people with short arms need reading glasses at a younger age, reading glasses don’t cause people’s arms to shrink. (124 characters with spaces) 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. We designed a cross-sectional retrospective and prospective observational study to assess whether there is an association between arm length and age when first requesting reading glasses in presbyopia. We evaluated individuals aged 38–55 receiving their first reading glasses for presbyopia (either currently or within the past year). We recorded age at first request for reading glasses, the refractive correction (additions) in each eye, and we measured arm length. Seventy subjects were included in the study. No association was found between arm length and the age of request for reading glasses or the severity of presbyopia at presentation. Even if this observational study had demonstrated a strong correlation between age of 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.