Word to denote the number of days/months of pregnancy
May I use "duration" if I mean the period from conception till the present moment and not till the due date? If no, what is the right word?

The sentence I need is:
If a person is pregnant (no matter how long her pregnancy lasts) she should get her doctor's approval for the flight.....
I'm interested in other ways to say the part in brackets.

It is said [irrespective of the term] in my language, short and simple. Anything I can think of in English is lengthy and seems to mean something different :(

Question

Word to denote the number of days/months of pregnancy
May I use "duration" if I mean the period from conception till the present moment and not till the due date? If no, what is the right word?

The sentence I need is:
If a person is pregnant (no matter how long her pregnancy lasts) she should get her doctor's approval for the flight.....
I'm interested in other ways to say the part in brackets.

It is said [irrespective of the term] in my language, short and simple. Anything I can think of in English is lengthy and seems to mean something different :(

Answer

You can say:

"I am ____ weeks/months" to talk about the "duration". 
Using the word "duration" will sound a bit awkward and unnatural.

Some other sentences would be:

When is your due date? (To ask someone's pregnancy)
or 
When are you due?

Answers could be:

My due date is ____ (date).
I am due in ______ (month).
I am due on _____ (date).

Some useful vocabulary would be:

1st trimester: months 1-3
2nd trimester: months 4-6
3rd trimester: months 7-9

Example:
I am in my 1st trimester.

Answer

If the pregnancy was already mentioned as in your example "If a persona is pregnant, ...", you could say:
- irrespective of how many months.
- no matter how far along.
- no matter the trimester.

Since you're saying "irrespective of", using "trimester" as in the third option is probably the best.  "trimester" is not in months or days, but because you're saying "the duration or stage doesn't matter", I think it conveys the same idea succinctly.

Answer

Person A
You shouldn't be going to work, you're pregnant.

Person B
Irrespective of the fact (that) I'm 8 months pregnant, I still have to go to work to earn money.

Answer

Thank you, ladies)) 
Stage is something that completely slipped my mind when I was trying to fix that sentence) I could proceed to it from the trimester, but I was too happy to think)) It's so annoying when such an insignificant thing takes so much time and effort)))

Answer

So - two things.
1.  At this point in time, only women can get pregnant.  So, while I would usually be all in favor of using gender neutral language, this is one of the occasions where you probably should use "woman" rather than "person."

2. "A woman in any stage of pregnancy should get her doctor's approval for the flight."