I don't understand the usage of で in this sentance

Question

This is from the headline of a news article in NHK News Easy.

日本の人口が減る　赤ちゃんが今まで「で」いちばん少ない

Can someone explain this one to me? Thanks!

Answer 1

で has many roles, but in this case it's a condition/situation/scope marker. It denotes the condition in which the modified word is applied. It's translated to various English prepositions, including "in", "among" and "under".

• 合計で100円　100 yen in total
• 割引で買う　to buy at a discounted price
• ～という仮定で話す　to talk under assumption that ～

今まで少ない (without で) would mean "(something) has been low/scarce up until now".

Answer 2

日本の人口が減る　赤ちゃんが今まで「で」いちばん少ない

"で" in the above sentence is difined by jisho.org here as:

で
Particle
2. indicates time of action

My attempt for the given sentence is as follows.
The population of Japan decreases. The number of babies is the smallest up to now.

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EDIT

I posted the closest one in jisho.org here as an answer, but since I got a down vote, I'll correct it.

I looked で up in various dictionaries, but I couldn't find an explanation that is perfect, but I think that the next one is better.

で is a particle that indicates time range for establishing a certain fact.

The fact is "the number of babies (born over a certain period of time) is the smallest" in the given sentence.