Its up to you reeally, talk to your doctor.
My doctor said its okay to do so
I am blonde all over at 32 weeks. The only problems I have had is my skin is super sensitive. Last time I got my roots done it burned my scalp and the bleach was only on for five minutes. My advice would be to make sure the bleach isn't sitting on your scalp, but usually it doesn't with just highlights.
That is not true...the above advice is not correct. The "risk" has only been two things: 1) bleach and peroxide sitting on the scalp for a long amount of time or 2) the fumes from the developer being ingested. The reason why KTT5 is not necessarily correct is that it doesn't matter what stage of the pregnancy you are in if you aren't in a WELL ventilated area and if you are letting it sit on your scalp. In other words, you'd be in the wrong hands if either of those were an issue. All salons are well ventilated and open (if it's a good and up to code salon). None of this "my friend highlighted by hair in the bathroom" stuff. Secondly developer and peroxide do NOT sit on the scalp when doing highlights. They are done in foils a minimum of a quarter to half inch from the scalp. I have worked with many doctors regarding this and reviewed many many studies. It is a great wives tale that it is harmful to your baby. The scalp is absorbant and does transfer to the blood stream as the rest of your skin does. So do not sit with bleach covering your whole head to go from brunette to blonde. And lastly keep ventilated. Like 2nd hand smoke, what you ingest can be harmful in large amounts. So you go get your highlights and enjoy your new golden locks!
You need to wait till your in your second trimester to be safe for the baby. There is too much developing in the 1st trimester