Caffeine intake and low birth weight: a population-based case-control study.
The authors conducted a matched case-control study to investigate the effects of caffeine intake during pregnancy on birth weight. From January to November 1992, in the first 24 hours after delivery, 1,205 mothers (401 cases and 804 controls) were interviewed and their newborns were examined to assess birth weight and gestational age by means of the method of Capurro et al. (J Pediatr 1978;93:120-2). The cases were children with birth weight < 2,500 g and gestational age > or = 28 weeks. Cases and controls were matched for time of birth and hospital of delivery and were recruited from the four maternity hospitals in Pelotas, southern Brazil. Daily maternal caffeine intake during pregnancy for each trimester was estimated. To assess caffeine intake, 10% of the mothers were reinterviewed at their households and samples of reported information on drip coffee and maté (a caffeine-containing drink widely used in South America) were collected and sent to the laboratory for caffeine determination through liquid chromatography. When instant coffee was reported, the weight of powder was measured using a portable scale, and caffeine intake was estimated from a reference table. Caffeine intake from tea, chocolate, soft drinks, and medicines was estimated from a reference table. Analyses were performed by conditional logistic regression. Crude analyses showed no effect of caffeine on low birth weight, preterm births or intrauterine growth retardation. The results did not change after allowing for confounders.