I took Metformin for the first trimester with DS, but that was coz of having PCOS (Metformin regulated my cycle to help me fall pg ) I believe it is category C for pregnancy (may have changed by now as they learn more about it tho).

But mine had nothing to do with sugar levels, they were all fine, mine was to do with insulin resistance. I didn't have any side effects from it either, apparently it can make you feel pretty yuck for the first couple of weeks, and it's best to gradually increase the dose to reduce that.

Hope you feel better soon with it.