This population-based prospective cohort study was designed to address the issue of maternal caffeine consumption during pregnancy affecting the risk of miscarriage before the 20th week of gestation. The study identified 2729 English-speaking, newly pregnant patients over a 2-year period from the Kaiser Permanente Medical Care Program, of which 1063 patients ultimately enrolled in the study and completed the required interviews and follow-up. Overall, patients were categorized into two groups: 1) those consuming > 200 mg/day or 2) those consuming < 200 mg/day based on the details of interviews and self-reporting diaries. For every 150 mL of a beverage consumed that study subjects reported, the authors estimated 100 mg of caffeine for coffee, 39 mg for tea, 15 mg for soda, and 2 mg for hot chocolate. Compared with non-users of caffeine (12%), the rates of miscarriage among women who consumed < 200 mg/day of caffeine (15%) and > 200 mg/day (25%) were significantly increased. The authors calculated an adjusted hazard ratio (aHR) of 1.42 for caffeine users of < 200 mg/day and 2.23 for caffeine users of > 200 mg/day compared to non-users. On initial analysis, caffeine intake was associated with a variety of additional risk factors: age > 35 years, prior miscarriage, smoking, alcohol consumption, and use of Jacuzzis. The authors then performed a stratified analysis of a number of confounders that did not change the overall effect of caffeine increasing the miscarriage rates. Additionally, the specific symptoms of nausea and vomiting were assessed as potential confounders and shown not to change the overall increase in miscarriage rates in patients consuming larger amounts of caffeine.
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© 2008 Elsevier Inc. Published by Elsevier Inc. All rights reserved.