Hi
Usage of mobile phones is considered safe .
If you are so concerned , check SAR value of your phone model on internet.
If SAR value is less than 1.6 w/ kg , it is whithin permissible limit.
There has been no long term studies on this topic yet. But this is the general consensus as of now.
Next Steps
Avoid investigations such as x-rays,ct scans, as they are definitely detrimental to unborn child.