From a health perspective overall, artificial sweeteners are very bad for health - avoid them at all costs as they are damaging to your body.

This is a good summary of the dangers of artificial sweeteners, if you're trying to get pregnant I would stay well away:

Emed - The Dangers of Artificial Sweeteners

Aspartame accounts for over 75 percent of the adverse reactions to food additives reported to the US Food and Drug Administration (FDA). Many of these reactions are very serious including seizures and death as recently disclosed in a February 1994 Department or Health and Human Services report.
There are 90 different documented symptoms listed in the report as being caused by aspartame. Not good for baby making I would easily assume