The paper "Declines in Unintended Pregnancy in the United States, 2008-2011" [1] by Lawrence B Finer and Mia R Zolna is linked by the CDC on their page about Unintended Pregnancy, and is a notable source of data on unintended pregnancies. This paper clearly states how they determined whether a pregnancy was intended:
"Pregnancy intention was defined according to a respondent's answers to a series of retrospective survey questions about her desire to become pregnant right before each pregnancy occurred. If she reported that she did not want to become pregnant at the time the pregnancy occurred, but wanted to become pregnant in the future, the pregnancy was categorized as mistimed. If a respondent reported that she did not want to become pregnant then or at any time in the future, the pregnancy was categorized as unwanted. We classified a pregnancy as unintended if it was either mistimed or unwanted; an intended pregnancy was one that was desired at the time it occurred or sooner."
When others cite statistics from this paper, this definition of "unintended" is nearly impossible to de-tangle from poverty: a reasonable respondent may very well indicate that their pregnancy was mistimed because of well-founded concerns, such as that they were not in a financially secure environment at the time. The paper treats such a response as an "unintended" pregnancy.
Careful reading of the paper reveals that there is evidence that poverty (at the time of surveying and/or at the time of pregnancy) causes respondents to retroactively rate their pregnancies as "unintended". This is a far less radical result than one may glean from casual discussion of such statistics.
[1] https://doi.org/10.1056/nejmsa1506575