There is forcing in fasting for pregnant ladies. If you are healthy enough, you can go on. But if you worry about the baby, you don't need to fast. Just qada' in other times.
I wouldn't recommend fasting during pregnancy as what you eat, and how often has direct effects on the fetal development of your child.
When I’m pregnant. I did not fast cause I have nausea and needs to eat every 1-2 hours recommended by my doc.
i will fast