When I was TTC I was extra careful and cut out all artificial sweeteners, and caffeine. I was not a happy camper!! The doctor said that 200mgs of caffeine a day were ok. But I still avoided it. Occasionally when I had a bad migraine, I would take a Tylenol and have a little coke.
My TCM said that you would be better of drinking a regular coke then diet coke. She said something with the aspartime was awful for TTC. Or even have a little coffee with whole milk and real sugar. So I listened! It was SO hard...as I was addicted to Diet Coke, I would go to the McDonalds drive thru just to get a large fountain Diet Coke!
I just saw this article and thought it was interesting. The first slide that comes up is "Limit Caffeine Consumption".
9 Natural Fertility Boosters
Limit caffeine consumption
Several studies have shown reduced fertility for women who consume more than 300 mg of caffeine each day. Fortunately, the threshold is high enough that you can still indulge in that morning cup o' joe, since the average 8-ounce cup of coffee only has 100 to 130 mg of caffeine. Don't forget, though, that black tea, green tea, chocolate, and some sodas also contain caffeine.
For women undergoing in vitro fertilization, however, the threshold is much lower: A mere 50 mg of caffeine—the equivalent of one cup of tea—can negatively impact success rates.
Alice Domar, an assistant professor at the Harvard Medical School who also counsels women dealing with infertility, suggests that you may want to further restrict your caffeine intake if you've been trying unsuccessfully to get pregnant, even if you're not doing IVF. Since only limited research has been done on the topic, Domar worries that further research may show that lower amounts of caffeine still impact fertility.