I kinda knocked up my attack party tanker and she now got the pregnant debuff which make her less tanky so I just wanna know how long would this debuff last

120 turns or 30 days.

Damn that's kinda long

There's a mod -part of the SfCRevamp - reduces the time by more than half.

The total pregnancy is 30 days.  There's no debuff for the first 10 days, then a mild debuff for the next 10, then a more severe debuff for the final 10.  

You can always go to "<GameDirectory>\src\core\variables.gd" and change the pregduration variable. The value is in turns (1 day = 4 turns).
That's what I usually do to set it to 10 days, which feels optimal to me, personally.