If and how well Rogaine, zinc, and biotin work for others is no indication of how well they would work for you.
Another consideration is that you may not experience hair loss as a side effect of Topamax. It's a potential side effect, not a certain one. We've had many people her who didn't. I took Topamax for nine months, and had no hair loss.
As with any supplements, we should always consult our doctors before using biotin and zinc. Even these "natural" substances have potential side effects and contraindications. Your doctor can also guide you regarding how much biotin and zinc to take since it's possible to take too much of them."
Congratulations on your pregnancy,