Enalapril is an ACE inhibitor which, as you rightly point out, should not be taken during pregnancy, during any of the trimesters.
Mifta's atenolol is a Beta-Blocker which works differently to ACE inhibitors. Beta-blockers don't carry the same risk during pregnancy as ACE inhibitors, although caution is advised.
I would suggest that you talk to your GP regarding changing your medication from an ACE inhibitor to an alternative anti-hypertensive drug. I can't really suggest an alternative as each person is individual so one drug may not be appropriate for another person.
Sorry, but hope it helps.