It's fine - unless you have them boiling hot - that's what the problem is with spas - they usually have water heating pumps in them that can cause overheating - regular baths don't.

There is another hazzard to watch out for when having baths when pregnant - getting stuck in there.

I was in the third tri & had major swelling of the ankles & when I tried to raise myself out of the bath I felt like my ankles would snap. Seriously, just snap. It was just awful. Thankfully my then DF was in the house & he came to the rescue.

I didn't have another bath for the rest of the pregnancy & during labour they couldn't have paid me to enter the big bath they had there for use during labour (even though I intended to use it originally).