Ask your OB/GYN - there are a lot of different opinions even among OB's about what you can and can not have.
My OB/GYN had no problem with me having a diet coke/day, a glass of wine/week (which I really never did) or tea. We went to Sam's Club and got Luzianne Decaffeinated tea and keep that around all the time now. I have learned to like tea without sweeteners, and it's a nice alternative to our awful tap water.
This exerpt is from the American College of Obstetrics and Gynecology's website:
Anderson BL, Juliano LM, Schulkin J. Caffeine's implications for women's health and survey of obstetrician-gynecologists' caffeine knowledge and assessment practices. J Womens Health (Larchmt). 2009;18(9):1457-1466.
http://www.acog.org/departments/dept_notice.cfm?recno=16&...
Objective: Caffeine has relevance for women's health and pregnancy, including significant associations with spontaneous abortion and low birth weight. According to scientific data, pregnant women and women of reproductive age should be advised to limit their caffeine consumption. This article reviews the implications of caffeine for women's psychological and physical health, and presents data on obstetrician-gynecologists' (ob-gyns) knowledge and practices pertaining to caffeine. Methods: Ob-gyns (N = 386) who are members of the American College of Obstetricians and Gynecologists' Collaborative Ambulatory Research Network responded to a 21-item survey about caffeine. Results: Although most knew that caffeine is passed through breast milk, only 24.8% were aware that caffeine metabolism significantly slows as pregnancy progresses. Many respondents were not aware of the caffeine content of commonly used products, such as espresso and Diet Coke, with 14.3% and 57.8% indicating amounts within an accurate range, respectively. Furthermore, ob-gyns did not take into account large differences in caffeine content across different caffeinated beverages with most recommending one to two servings of coffee or tea or soft drinks per day. There was substantial inconsistency in what was considered to be "high levels" of maternal caffeine consumption, with only 31.6% providing a response. When asked to indicate the risk that high levels of caffeine have on various pregnancy outcomes, responses were not consistent with scientific data. For example, respondents overestimated the relative risk of stillbirths and underestimated the relative risk of spontaneous abortion. There was great variability in assessment and advice practices pertaining to caffeine. More than half advise their pregnant patients to consume caffeine under certain circumstances, most commonly to alleviate headache and caffeine withdrawal. Conclusions: The data suggest that ob-gyns could benefit from information about caffeine and its relevance to their clinical practice. The development of clinical practice guidelines for caffeine may prove to be useful.