Consumo de cafeína entre gestantes e a prevalência do baixo peso ao nascer e da prematuridade: uma revisão sistemática Caffeine consumption during pregnancy and prevalence of low birth weight and prematurity: a systematic review

Realizou-se revisão sistemática sobre o consumo de cafeína em gestantes na ocorrência de baixo peso ao nascer e prematuridade, enfocando métodos para quantificação deste consumo e confundimentos controlados na análise. A revisão consistiu na busca de artigos publicados de 1996 a 2006 nas bases MEDLINE, LILACS e PubMed, utilizando-se as palavras-chave: "caffeine", "coffee", "low birth weight", "birth weight", "preterm", "premature" e "prematurity". Dez artigos foram selecionados. Os métodos utilizados para quantificar o consumo de cafeína foram: questionário de freqüência alimentar semiquantitativo - da dieta ou apenas de produtos cafeinados, sendo um do tipo auto-aplicado; recordatório alimentar; perguntas sobre tipo e modo de preparo; análise de amostras; e dosagens urinária e plasmática. Em três estudos revisados, o consumo elevado de cafeína associou-se com baixo peso ao nascer e/ou prematuridade. Contradições nos achados devem-se a dificuldades na mensuração do consumo de cafeína; às fontes abordadas; a variações no preparo e na quantidade consumida; e ao tamanho amostral. Não foi demonstrada associação entre ingestão moderada de cafeína e crescimento fetal, sendo necessária uma avaliação mais precisa do consumo dessa substância.<br>This article reports on a systematic review of studies on caffeine intake during pregnancy and prevalence of low birth weight and prematurity, focusing on methods to quantify intake and control for confounding. The review consisted of an article search from 1996 to 2006 in MEDLINE, LILACS, and PubMed, using the key words: "caffeine", "coffee", "low birth weight", "birth weight", "preterm", "premature", and "prematurity". Ten articles were selected. Methods used to quantify caffeine consumption were: semi-quantitative food frequency questionnaires for diet or only caffeinated products, including one self-applied questionnaire; food recall; questions on type and method of preparation; analysis of samples; and urine and plasma caffeine levels. In three studies, high caffeine consumption was associated with low birth weight and/or prematurity. Contradictions between studies may be due to difficulties in measuring caffeine consumption; assessment of different caffeine sources; variations in the mode of preparation and amount consumed; and sample size. Association between moderate caffeine consumption and fetal growth was not demonstrated, so a more precise measurement of caffeine intake is necessary

The impact of hydrogeochemical processes on karst groundwater quality in arid and semiarid area: a case study in the Liulin spring area, north China

Karst groundwater is the major source of water supply for economic development and drinking water in Liulin spring area, north China. Thus, karst groundwater quality and its variation have aroused wide public concern. The primary hydrogeochemical processes that dominate karst groundwater quality, including dissolution of carbonate rocks and evaporite, mixing, and dedolomitization, are analyzed by hydrogeochemical method in combination with multivariate statistical theory and computer simulation technology. The results show that the redox state of groundwater environment transforms gradually from oxidation state to reducing state with increasing temperature and total dissolved solids (TDS) and decreasing pH value along flow path. The hydrogeochemical types of groundwater range from HCO3-Ca·Mg to Cl·SO4-Na. The Ca2+, Mg2+, and HCO3 − in karst groundwater mainly originate from dissolution of calcite and dolomite. Dissolution of calcite occurs in infiltration of rainfall into soils and unsaturated zones and then reaches to saturation before arriving groundwater level. Though saturation index of dolomite (SID) is greater than 0 in most of the samples, dolomite still dissolves along flow path due to the dedolomitization. The SO4 2− derives basically from the dissolution of gypsum rather than oxidation of pyrite. The dissolution of gypsum causes dedolomitization that increases the concentrations of Ca2+, Mg2+, and SO4 2− while the concentration of HCO3 − has smaller changes. The concentrations of Na+ and Cl− are mainly controlled by dissolution of halite. The enrichment of Na+ relative to Cl− in most samples may result from leakage of surface water enriched Na+ and dissolution of mirabilte fragments