If soda crackers don't solve the problem, the pregnant runner might want to take a break and wait a while before returning to running. Anaerobic work is not necessary, because competitive goals must be abandoned during pregnancy. As the belly becomes more pronounced and morning sickness wanes, the pregnant woman may feel better than ever. Mileage should remain sub-normal, but needn't be drastically reduced unless the runner feels uncomfortable. It does no long-term damage to a running career to stop running, so she should continually listen to her body and decrease if necessary.
Moderation is the name of the game.
A pregnant runner should not participate if it is a very hot day, or if she tends to be compulsive and knows that she may not be able to hold herself to a reasonable pace. Developing a relaxed attitude can be quite a learning experience. I tend to be an unreasonably fast starter in my non-pregnant races. I recently ran a four mile road race while four months pregnant. Consequently, I ran the first mile 45 seconds slower than usual.