To the Editor.
—Infante-Rivard et al1 conclude that caffeine intake during pregnancy causes spontaneous abortion. They cite our study of karyotyped losses, but disregard our interpretation.2About half of spontaneous abortions have chromosome aberrations. This diversity allows application of two criteria to assess causality: (1) an association specific to a particular type of loss and (2) the time of exposure coherent with pathogenesis.3Chromosomal aberrations arise no later than conception, and some long before; over 90% of conceptuses are nonviable and abort spontaneously. Exposure to caffeine after conception cannot cause aberrations, nor is it likely to produce detectable increases in loss rates because aberrations are already so highly lethal. By contrast, causes of chromosomally normal loss might operate either before or after conception; causal effects of exposure during pregnancy are biologically plausible.We studied 899 karyotyped cases and 1423 controls (deliveries, ≥28 weeks). We compared cases with
Kline J, Levin B, Kinney A, Stein Z, Susser M, Warburton D. Fetal Loss and Caffeine Intake. JAMA. 1994;272(1):27-28. doi:10.1001/jama.1994.03520010037016